Can't get access to a nice mirror? Or you want to try something different? Check out my video on Background Oriented Schlieren (BOS): th-cam.com/video/VCUN59x0LF4/w-d-xo.html
@@aether222 You can use your phone without a problem. I would highly recommend putting it on a tripod though. You can get rid of vibrations (as I show in that video), but it's much better if you use a tripod.
@@JoshTheEngineer What did you think of my idea of using computer methods to further enhance optical Schlieren photography? If computers can enhance regular video to show Schlieren so well, surely some method could enhance optical schlieren to make a super sensitive system?! (even if it needs a version that works with brightness or colour not translation).
Wow, great video! Thank you for the detailed explanation. I was going to do some experiments with a less-then-opticaly accurate parabolic mirror and you saved me from a lot of wasted time.
Thank you! I'm glad I could help. As you saw at the end of the video, the bathroom mirror produced pretty poor results, but it did technically work. So it ends up being a trade-off between price and quality. Depending on your application, you could start with something you have lying around, and if it doesn't give you what you want, then a move to a higher optical quality might be a good idea.
That's a cool set up! I like that you used a commercial one to show the difference in quality of the image. It made realize i didnt have to get fancy just experiment with this type of photography. It would be a cool experiment to do in a middle school or high school physics class too, for the teachers out there teaching kids about STEM. Next time you do this, you can try using the spot meter on your camera, your camera will only ready a specific point instead of an area. If you put your nikon on aperature priority, set it to the smallest f/22, with a spot meter (exposure settings (AE, scroll using the wheel, find spot)), you wont have to fiddle around with the exposure compensation as much, or might be able to go darker to get. more contrast which seems key to this type of imaging. Closing your windows would've helped to, your camera wont try to read the ambient light, it would just over expose the experiment. Thank you for taking the time to make this really in depth video! i am taking a compressible flow class and saw this technique being used for past experiments, did some google searches and found some neat videos, yours by far the best! I am a photographer and engineer so this experiment tickled my fancy haha. Good work!! =D
Thanks! Yea, this setup is super simple and would make a great display for some STEM outreach. That's been on my list of things to do for a science fair or something, now I just need to find the time. Good advice regarding the camera settings. I always just default on matrix metering because that's what I mostly use when I'm outside shooting. Unfortunately the blinds on my windows are what they are, and let quite a bit of light in even when they're fully closed (although after looking at my video again, I noticed I didn't even close them). I'll try the small aperture and spot metering next time I set it up. Thanks for the info! Good luck in your compressible flow class. It was one of my favorites when I took it in undergrad. I actually have quite a few compressible flow videos on my channel if you ever get stuck.
Thanks for this great video. I've been trying to make a schlieren effect set up for quite some time now, but I thought it would require expensive instruments and tools. After seeing this video I made a quick try with a commercial mirror and I guess it will be possible to make it work.
Great tutorial. Thanks for writing out such comprehensive details. Your explanation of how it works gets the point across better than any other professional schlieren mirror video I've seen. I think I am going to try this out myself.
Thanks, I appreciate it! There are a lot of other nice videos on TH-cam showing peoples' setups and results (some mentioned in the video description), but I didn't find any that laid out step-by-step how to make a setup at home, so I thought it would help others who wanted to do it themselves. If you get stuck, feel free to ask me questions.
I recently discovered Schlieren imaging. I want to build one myself. There are a few variations that I suggest to you should be investigate. VARIATION #1 You used a vertical position of the razor blade. How different the image would be if the blade was horizontal? Comparing both images vertical/horizontal razor blade position would be interesting. Along the same line, how about puting the razor blade a different angular increments and compare the resulting images? For example, you can choose the angular positions of 0, 15, 30, 45, 60, 75, 90, angular degrees. VARIATION #2 This is something I saw from another TH-cam video. They used colored light filters instead razor blade. This gives a far better result because the image is no longer blocked off, but colored. the resulting image gives far more visual information. Another similar variation is to use use two colored filters side-by-side in place of the razor blade. This seems to give the best result of all because the surface of the gradient becomes visible at both poles of the gradient. Another similar variation would be to find a color filter that changes from one color to another. This may be from one color to full transparency. This type of color filter might be harder to find, but they would hold good results because no information about the image would be lost for contrast. VARIATION #3 Use a polar light filter instead of the razor blade. You can use the polar light filter in the cheap 3D glasses given in movie theaters when they show 3D projection movies. Polar filters have a direction up/down or left/right. You can experiment with that in the same way as with the razor blade. First you try one filter replacing the razor blade and see what the result is. The filter might block off too much light and acting like a razon blade. Then you can try two polar filters side-by-side with one having vertical polar direction and the other having horizontal direction. I imaging that the light intensity might have to be increased significantly.
TH-cam will always amaze me... Why when i search for videos like this, i only find "crappy" ones or others that have nearly to information or details, only to get recommended videos like this and it is almost a decade old. Why can't i find them on my own ffs?!
Oh, thank you so much. I was trying to make Schlierenfotographie for years and at all the sites were I have been everybody talks about putting the camera at 2f. So it never worked. Your video gave me the clue needed that it must sit on 1f. So obvious. I thought I messed up some other component. Now it works. Do you think that one can observe smaller differences in refractiv index of the fluids with better optics?
You're welcome! I just want to make clear here though that in this double-pass (single mirror) system, the light source and knife edge are in fact located at 2f. That is, two times the focal length of the spherical concave mirror. A better mirror is the easiest (though probably the most expensive) way to get better images. You can also change sensitivity with the knife edge. It will also depend on the size of your light source and the tightness of the focused spot.
that is even more humane, wow im surprised. im like that myself, did not expect that :D i just share it and seed ideas into the world. still, for peoiple without acces to a 3d printer, you could offer a starter kit :d well balanced etc, or a little booklet i dont know :D keep up the awesome work!
do you often engineer projects etc? im working on a 3D ufo model that i think could work, like a drone only everything doubled in xyz like rotors on top and below working in tandem. im looking for someone with engineering experience for a few pointers perhaps. :0 some one who likes to help save this world :)
Hello! I was wondering if why we need a small light source. What happens if we use a larger light source? Thx for your video, it helped me a lot in understanding Schlieren photography.
amazzzzzzzzzzzzzing.. and really loved it.. I would try to buy some good quality mirror.. but did you try this with even more easy using MOBILE's Camera with manual focus or something?
if the LED is placed at 2f position and the viewing angle of the LED is too large does that mean not all of the reaches the mirror and being reflected? if thats the case does that mean i need to use the tangent formula and calculate the half angle of the LED to choose the most appropriate one?
Kudos... well done. A question: if you wanted to capture a sneeze or breath, let’s say an area a little bigger than a head, that would require a mirror of maybe say 12-15 inches. Obviously a quality scientific mirror would get pricey... any suggestion for an “adequate” solution? Perhaps a solar capture plastic mirror? Obviously not “fine”, but perhaps better than the cosmetic mirror. Again, this is a well done demonstration. I showed it my son in law, his response was two simple words... “mind blown”.😉
Thanks! Yes, mirrors can get quite expensive, especially nice ones that you need for schlieren measurements. One method that doesn't need a mirror is called background oriented schlieren (BOS). I recently made a video going through an entire DIY setup that might interest you (th-cam.com/video/VCUN59x0LF4/w-d-xo.html). You might have some trouble getting it to be as sensitive as a conventional schlieren setup, but this recent video by LaVision shows how sensitive it can be (th-cam.com/video/kYJvU81DKgk/w-d-xo.html&feature=emb_title). Note that LaVision is a company dedicated to flow diagnostics/visualization/imaging, so what they show is going to be hard to achieve at home with a simplified setup, but you can get pretty close.
+JoshTheEngineer do you think it will work if 1 foot behind the razor blade we placed a white paper as a screen so we get the image? I mean not to use a camera
That should also work, since the camera is mainly there so you can record images or videos. You might also notice that if you take the razor blade out of the setup, you can place a piece of paper where your camera would generally be, and you should still be able to see something that looks like Schlieren, but is actually called shadowgraph.
Holy smokes dude. I had the 2¢ version of how Schlieren imaging worked before I searched the term and found your video, and by the 1:38 mark you've made it clear the whole trick is the same interaction between point source light and atmosphere that makes stars "twinkle," and described how to recreate it consistently over a variable distance. That's the whole answer to how to build one, but I'mma still watch the rest of the whole video out of respect and expect to learn a hell of a lot more. (Edit: mild dysgraphic moment)
Great work Josh! I have a question tho... why is it better to use a spherical mirror instead of a parabolic one? Since parabolic mirror focus collimated light without introducing spherical aberration I fail to understand why shperical mirror is the best choice. Cheers
Thanks! The spherical mirror is needed for the double-pass schlieren system, whereas the parabolic is needed for the Z-type schlieren system. The one I show in this video is the double-pass, and only requires one mirror. I'll probably make a video on the Z-type system at some point, but it requires two mirrors. You're right that the parabolic mirror collimates the beam, but we actually don't want any collimation for the double-pass method. The spherical mirror is used because if you locate you point source twice the focal distance from the mirror, it will reflect off the spherical mirror and focus back down at the same 2f distance, which is then where we place the knife-edge. For the Z-type system, you place the point source at the focal length of the parabolic mirror, which then collimates the beam, and then a second parabolic mirror takes that collimated beam and focuses it down at one focal length, which is where we place the knife-edge. There are pros and cons to both types of systems, but that's the reasoning for the different mirrors.
Is it possible to see inaudible frequencies that are being broadcast into a house? I am seeking a way to trace their origin. I would really appreciate any information or advice you could give me. Thank you for your video. Very well done!
Thank you! The sensitivity is realistically going to be too low to see those sound waves, but there are certain instances where you can see them, for instance when you set up a standing wave. There are some demonstrations of schlieren being used for sound wave visualization that you can take a look at (by the Harvard Natural Sciences Lecture Demonstrations).
Thank you! I will build a set and put the final result on my tranparent paper paravant which seperates my private space from my working space. Customers will see the result but not the setup. THANK YOU!
WHAT A NICE VIDEO!!!! but,I think in this system the light has passed the Density variation region twice， I think，it will has some infulence for this system。
Thanks! Yes, in this setup with only one mirror, the light passes through on the way to the mirror, and then again on its way back to the camera. A Z-type system is a little more straightforward in that the light only passes through the region of interest once, but you also need to buy an extra mirror.
Hello josh, I'm 15 and I from France, in high school we have to do a project in groupe of 2 or 3 about the topic we want and the final mark of this project count for the baccalaureate. So I think that in our project we will do this experience : first we'll put a brick behind a ventilator, then we'll put a little car (a toys) behind the ventilator. thanks to your tuto, we will be able to see what will do the air and we will be able to compare the effect of the ventilator's air on the two objects and the effect of the objects on the ventilator's air. Could you tell me If you think it's a good or a bad idea? I don't know if you managed to understand what I mean so I'm sorry if you don't. Thank you a lot for your video !
Thanks! And yes, absolutely. Back when made this video I had taken some images with my Samsung phone and it worked just fine. You'll have more control with a dedicated camera, but you'll absolutely be able to get nice images/videos with your phone.
Yep! You can just take out the camera and hold up a piece of paper a little farther back behind where the camera was. The farther you move the paper back, the larger the image gets, but it will also get dimmer. However, you'll be able to see the effect no problem. Note that the image will be upside down. You can also switch between Schlieren and shadowgraph by pulling out the knife edge.
I Try to set up the system . 1,And I do some change ,the angle of this system is bigger. I see the candle and the candle in the mirror.both of them have the shadow. 2.I analysis the image by matlab and i find one half image is dark a little . I think it in relation to the knife cut the focus .
To make sure you get the best image in the end, I recommend leaving out the knife edge until you can see that you get nice uniform light all across the mirror. If the light is uniform over the mirror, that means you have a good quality mirror, and your camera is aligned in a good location to then put the knife edge in. The next step is then to put the knife edge in before you put the candle in. You should still have a uniform distribution of light on your mirror, but it will be a little dimmer because you're cutting out some of the light. Finally, you can put the candle next to the mirror, and you should get some nice images.
@ JoshThe Engineer : I have seen this effect many, many times in the shadow of my car's hot roof. Also, I see it sometimes on the wall of my bathtub when there is a hot bath. How are these situations working? Also, I wanted to ask how that NASA used this technique on a full size aircraft to show the shockwaves. I had never seen this technique used on anything but small objects in a lab environment. I skimmed the article, but will continue to research how they did it. I'd love to be able to use the technique to visualize the airflow around my car. www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html
They use a method called Background Oriented Schlieren. I actually made a video about how you can use this method at home, and I provide some simple code that will help you process your data: th-cam.com/video/VCUN59x0LF4/w-d-xo.html The NASA data from those now-famous pictures was taken from a plane flying above the target plane, and looking down at the desert floor. You can also take these large-scale images by pointing your camera at the sun and using an appropriate filter (I wouldn't try this one at home as a beginner, but you'll find papers on it). Maybe I'll make another video where I go into more detail about their measurements, but my video at least shows you how you can do it at home. Hope that helps!
@@JoshTheEngineer Thank you ! I saw other videos where the planes fly in front of the Sun, but this image puzzled me, because the planes in this instance were seen from above. I assumed maybe they were just superimposed in Photoshop . Thanks for clearing that up about the bright desert floor. Your video is absolutely, just the thing I was looking for! I will be sure to watch it in it's entirety later. Thank you for posting!
While the optimal mirror for this double-pass system is a spherical concave mirror, a parabolic mirror will still work okay. For the Z-type (two-mirror) schlieren system, the parabolic mirror is the optimal choice. I'm currently filming a spherical vs. parabolic mirror comparison for schlieren systems where I'll go over why you can use either, but also how performance is degraded depending on which system you're using it in. I'm also editing a Z-type schlieren system video, so if you have two telescope parabolic mirrors, you can get some really nice images from that system.
Thanks for making this video. I saw the Schlieren effect in a pilot training film describing how moving air causes lift in an aircraft wing. That was in 1967, and I never forgot it. I also never saw it again until I stumbled onto your video. Thanks again!
Does it work if you don't use a point source, but instead use a light source that produces beams parallel to the principal axis of the mirror, and place the blade edge and camera at the exact focal length instead of twice the focal length?
That's actually sorta what the Z-type Schlieren system does. You're essentially just skipping the first mirror part, which collimates a beam from a point source located at the focal point of a parabolic mirror. Then after the collimated beam passes through the region of interest, another parabolic mirror focuses the light rays down to a focus, where a knife edge is located, and then into your camera.
Amazing video. I have a quick question, if you have the time. What is the minimum temperature difference that can be shown in this setup? Can heat rising from a human body be shown like this? Thanks very much.
I will be as brief as possible. ONE the presentation if complete, that is numbers, calculus, formula, and subsequent derivatives thereof. Thank you so much for this great chance at a little know idea/subject! YET, again, let me say the math, means and hows to make such a LANDMARK devise is not done by too many (no doubt due to the guys like me that are gonna ask for necessary improvements...), WHAT, please is the absolute (as pragmatic for homebuilders like me and you ) diameter of that "PIN HOLE." I built the devise, but it doesn't work. Indeed my entire set up was due to an incorrect "pin hole" in that foil over the LED. Thanks again, in the name of DIY and the movements like demonstrating a "better way" sense 2000 pt Secret name of Most High.
I know this sounds ridiculous, but if one cannot get a precision mirror. Take lots of math and time, but give cheapo mirror aprox. 3k spin (or more RPMS) theoretically, this should account for those imperfections in your mirror from the drug store. Again, lots of time AND math to get a parallel mirror "perfectly" spinning around, but yeah the imperfections "melt" together, while the mirrored light is concave. This is said in lieu of the movements and all the utterances to live by sense the 2020 Paradigm Shift. Thanks again. If I'm wrong, I'll Eat my fricken plastic enhanced coffee cream!
Hi! I believe I have everything needed at home. The mirror is one of those that you put in the bathroom I hope it'll work! I'll find a razor blade somewhere in the house and there must be a LED lying around as well. My only problem is that my camera is a semi-DSLR?(if there's such a thing ahah) By that I mean you can't zoom in and out manually and you can't really adjust the exposure. Will it work in a super dark room? I'll try to cover any lights or maybe put a long cardboard box between the camera and the mirror. I don't know, if you have any suggestions please help me! This project looks so cool
Hello! The mirror I use at the end of the video is a bathroom mirror, so you can see that maybe you won't get the crystal clear images like I get with my good mirror, but you should still be able to get something. If you don't have a razor blade lying around, you can always use a knife, just be careful. You can use any light source, even a light bulb, as long as you put a cover over it and poke a little hole in that cover to make a quasi-point source. I've gotten good results with my DSLR, my point-and-shoot circa 2005, and with my phone. The main problem you'll run into is that you won't be able to zoom in on the mirror, so it might be sort of small on your screen or in you picture you take. That's the problem I have, since I don't have a lens that zooms far enough. Your camera should definitely have some sort of exposure setting. All three cameras I just mentioned have the option to adjust the exposure manually, even my phone. I would just check the manual for the camera. It's easier if the room is dark, but as you can see in my video, I'm taking this video during the day, so that should work just fine too. Good luck!
Hi! I'm a high school student in korea and I have a question. If light rays bend as the air density changes, then does it mean that light always bends because the density of the light always changes?I went to this site goo.gl/gI1YQq where you recommanded to all viewers. And the question just popped up! Please answer my question if possible.
Hello Josh, I have a stupid question for you concerning night vision cameras ??? Since the camera uses infrared light to enhance the light around the lens this can easily be seen with an app on a smartphone. This defeats the purpose of in cognito of the camera in the first place. What can I do to be able to film what is going on to about 400 feet distance with good resolution ??? Is there something you can be kind enough to guide me in the right direction if there is something out there in the field with a reasonable price ???? Thanks a bunch and peace. Your video is very well done with the right ratio of information and whiteboard illustrations. Thanks a bunch and peace too.
+joemonster55 That sounds like something that I would definitely be interested in doing (i.e, make a shock tube with a little viewport and a place to insert a mini model). However, this will take some more time to think about and execute. I do have some other interesting ideas about how to use this setup to visualize shock waves from bullets, etc. I will probably post a couple more videos describing minor perturbations to this setup first, such as using the external camera flash instead of the LED. But if you have any cool ideas, let me know!
+JoshTheEngineer I would also be interested in a DIY video of a shocktube to see some shockwave (If the cost can be kept down like we see in this video). Can a simple paintball gun produce a supersonic shockwave if we fire it into low pressure air?
The shock tube idea is definitely still on my to-do list for the future. I have so many other videos I'm trying to work through at the moment, but I'm going through some calculations for a shock tube design that would result in shocks strong enough to be seen by a simple Schlieren system like I showed in this video. I also wanted to do a video on Schlieren images for some sort of gun or projectile launcher, so that's in the works as well. I would have to look more into paintball gun firing velocities, but I can guarantee that you would see something coming out of the front. What you see and with how much sensitivity will be dependent on the gun characteristics and the sensitivity of the Schlieren setup (focal length, mirror quality, light uniform-ness, and so on).
Hi. We're trying to make a Schlieren set up for our research. And we want to use a 50 cm Diameter mirror. We'll be making our own mirror using space blankets. Is it possible that we can still get images???
I think you'll definitely get something, though I'm not sure what kind of quality it will be. I had wanted to try this setup with the mirrors that NightHawkInLight made, so let me know how they work!
I have been trying to get this to work for a few days now. I am using a DSLR camera, a concave mirror with a 24" focal length and a razor blade setup just as yours is in this video. I am getting to a point where the mirror appears gray-ish, like in this video. However when I turn any heat source on in front of the mirror, nothing shows up in the image. Any tips? I have tried a couple different light sources including an LED flashlight with the reflector taken out and a black cover over the top with a hole in it and an LED point source like yours in the video.
I'm assuming you've pretty much set up everything the way I do it in the video, so let's work through a couple scenarios and see if that helps. If you remove the knife edge completely from your system (and you don't put anything in the beam path, which I'll just call a candle from now on for simplicity), you should get a uniform light distribution on your mirror as viewed through your camera. If you do, that's a good first step. The next thing to do is to place the knife-edge in the beam path, at the point where the beam focuses down to a point, still without the candle. If you cover up half the beam with the knife-edge (you'll see half the beam spot on the knife-edge, even though it'll be small), then you should see your intensity go down, but it will still be uniform. The more you move your knife-edge into the beam, the dimmer the image on your camera will get, but it will always stay uniformly lit. After the knife-edge blocks the beam, you obviously won't see any light passing through to your camera. If everything makes sense up to now and is working like I mentioned, then you should bring the knife-edge back to the point where it's covering about half the beam spot at the focus. As we saw before, you'll have a uniformly lit mirror, but it will be dimmer than if there were no knife-edge in. No place your candle as close to the mirror as you can without it burning or heating up the mirror, maybe an inch away. You should see something now on the camera. If you pull the knife-edge out of the beam path slowly, then you'll see the sensitivity decrease, and the mirror will become uniformly lit at the full intensity of the light source. If you move the knife-edge farther into the beam spot, you'll still "see the heat", but the background intensity will go down. If you look at the video that the TH-camr "brusspup" posted, you can see in that setup that he has most of the beam spot covered by the knife-edge, which is why the background looks so dull and gray. I personally don't like the way that looks, so I usually do about 50% coverage, and then adjust back and forth until I get an image I like. A couple of other things to note. Orientation of the knife-edge does matter. If you're looking for horizontal gradients of index of refraction, then you need to orient the knife-edge vertically, as I do in the video. If you are looking for vertical gradients of index of refraction, then you need to orient the knife-edge horizontally. Or you can do it at an angle and be slightly sensitive to both. For a candle, put the knife-edge in vertically because the index of refraction changes abruptly in the horizontal direction. Also make sure that your return beam spot is coming back as close to the LED source as possible (within reason). This will eliminate double images. You might need to adjust your exposure compensation on the camera too, because as you can see in my video when I bring it back to 0 (no compensation), you can't see much on the mirror. Another TH-cam comment mentioned that I could have used spot metering as opposed to matrix metering for my exposure, where the spot would be fixed on the mirror such that it was correctly exposed for the mirror light. Hope something in this response helps with your setup! If it does, let me know what fixed it.
I have two meade LX telescopes that have nice mirrors but failed electronics. An 8 and a 12 inch. Nice basement to set it up in for the distance. Time to get busy!
Hi Josh, I tried to set up my 8 inch Meade SCT last night. I took the corrector off along with the secondary mirror. They aren't suited for this. The focal point of the primary mirror is 16 inches where it is folded by the secondary into a baffle toward the visual back. The mirror also has a good sized hole to fit the baffle. I had considered it would be a problem way before starting but played with it anyway. Any ideas? I did notice if I place a bright LED flashlight smack in front at 16" I get a focal point across the room on the far wall. Unless I am confused. I thought you were focusing on a pinpoint with your camera. I'm not clear how you could resolve that tiny point into something useful. I'll watch it again.
I managed some butane. I did not use the blade to block light. Maybe the camera was offset enough. Actually I was almost 2X distant from the light source focal point. th-cam.com/video/2BSEaf9Atro/w-d-xo.html
Thank you for your post! This is the best video I have ever seen about Schlieren-Shadow imaging. I successfully built a mini one with a concave mirror that has a f=50 mm. Most of the parts of mine were 3d printed. I can see hot air, butane and helium. But argon, not really. The mirror I used was a scientific grade concave mirror with aluminum sputtered for UV. Also I used green LED instead of a white one due to the fact that refraction of light is positively related to wave length. I think a blue one might work better. One quick question, have you thought about build one with 2 concave mirrors? That should give you "True" Schlieren imaging and better sensitivity. BTW, I don't think the focal distance is the major factor that determines the sensitivity or image quality. Instead, I think the quality of the pin-hole and the razor blade are the keys. Please correct me if I am wrong about it. Thanks again for you post!
Thanks for watching; sounds like you have a pretty cool little setup! I definitely want to make a 2-mirror Schlieren setup at some point, but the reason for making this one is that it is the cheapest for the frugal DIY-er. It's also pretty easy to construct and align everything. I'll probably get around to make a more scientific setup at some point. There are a lot of different aspects of the system that affect the sensitivity. I mentioned the mirror as (arguably) the most important component because of the uniformity of light that we see in the images. If the mirror is poorly constructed, you'll get some dark spots, and the light source won't focus back to a perfect point. This then makes the razor blade placement a little tricky. I do think that the focal length is important for sensitivity because if you think of the divergence of the ray from it's nominal (non-refracted) path, the longer the focal length is, the farther the displacement from its final location it will be when it gets to the 2f distance. This makes it more sensitive to pick up lower density gradients. However, like you mention, knife-edge placement is also key. You can pick up different gradient directions by aligning the knife-edge vertically, horizontally, etc. You can also block all the undisturbed light as well by making sure the knife-edge covers the center of the beam, and then you'll only see the refracted light. There are a lot of different opportunities with regard to the knife-edge design and placement that will affect what you see in the image or video. So it really ends up being a combination of many components that influences the sensitivity and images you see, and it's hard for me to confidently say that this one component matters more than that one without getting into some more advanced optics equations.
Hey Josh, Thanks for the video. I have a question by the way. I saw your reply to one of the comments below, where you mentioned that the first step in Schlieren is getting a uniformly lit mirror. What exactly needs to be done to achieve this? I am using an 8" dia, 30" focal length mirror with a Nikon D610 for visualization. I can visualize the flow patterns, but my mirror is not uniformly lit and the image is just focussed on a small portion of the mirror. What should I do to get it over the whole mirror?
No problem! The easiest way to get a uniformly lit mirror is to take out the knife-edge completely, and place your camera (behind the point where the light focuses back down to a point) in a location where you see the mirror completely filled. You've probably tried this already, so here are two more things to check. First, make sure your light source is diverging enough such that it completely fills the mirror. As an extreme example, if you use a laser point without a diverging lens, the light spot you'll see in your camera will only be as big as the laser beam diameter. You can see in my Laser Schlieren video (th-cam.com/video/JvHZT_wBpUE/w-d-xo.html) that when I use a diverging lens, the light overfills my mirror a little bit, which is better than it under-filling the mirror. Second, make sure your aperture (F-stop) is open as wide as it can go (lower numbers). I was trying to take some high speed Schlieren a little while ago, and it turns out I couldn't attach my lens of choice to the camera because it would auto-adjust the F-stop to the smallest aperture (highest number). I had to use a manual-aperture lens with that body so that I could make sure the lens was wide open, which didn't restrict the light entering the camera. Try checking this, and let me know if it doesn't solve the problem.
12:45 look at the arrow of light a few inches from the mirror, watch how it stretches out and disappears right as he reaches the focal point. Does anybody know what that is or how the camera can see it?
Thanks Josh, awesome video with great explanation. I have a question, would placing the light source and knife edge at the focal point work as well? since at focal point the light will also come back as a dot just similar to 2f point. Also, is the led bulb collimated? Does the light source need to be collimated? Thank you!
You're welcome! If you placed the light source at the focal point, the light would actually leave the mirrors collimated, and wouldn't focus back down again. This is actually what the Z-type Schlieren system does. You place the light at the focal point, collimate it with a mirror, then use another mirror to focus the collimated light back down to a point at the second mirror's focal point, which is where you would place your knife edge. This way, you get collimated light through your object of interest. The LED is not collimated; it emits light in all directions. You don't want a collimated light source, because it needs to diverge out to fill the mirror. Lasers are collimated, which is why in my other Laser Schlieren video, I use a lens to diverge the light so it encompasses the mirror.
Thanks, Josh! I thought it's just a good video, but when I saw that mirror stand made from cardboard and adhesive tape, I instantly clicked on "subscribe". DIY in its purest form. Love it!
Cool video. To show the turbulence caused by the heat of the candle it is better to have the candle several centimeters below the center of the mirror. The column of rising air above the candle is laminar for a few centimeters then transitions to turbulent flow. The turbulent flow is more interesting to watch.
Thanks. You're correct, I could have moved the mirror up a little. However, showing the laminar part is a good way to show how the knife-edge affects the results you're seeing. I didn't switch the knife-edge in this video, but it would have been a good explanation to rotate it 90 degrees, and show that you don't see any gradients.
im sure you probably know XD but all radioshacks are closed now, is there anywhere else you suggest getting the LED and if so what specs LED did you use??
Yea, unfortunately they were starting to go out of business when I made this video. If I were you I would just buy a pack of LEDs off of Amazon. You can get a bunch of them for pretty cheap. I just used the standard 5 mm clear LED, but you can honestly use whatever kind you want.
You need something sharp/straight so that it has a well defined edge to cut off the light. You also need it to be thin (axially along the beam path) because if it's too thick, it will get in the way of the beam as it's focusing down to the point. A razor blade just happens to satisfy both of these limitations, and they're inexpensive. You should try it with a different object, and see how that changes your results!
The double-pass nature of this particular setup makes it more sensitive to distortions. So it's really the sensitivity that's increased, not necessarily the clarity of the picture/video.
Very nice! For years, I have thought about this kind of imaging and not known how they are made and finally I know and would even be able to do it myself if I like to. Many thanks!
The separation distance between the light source and mirror is dictated by the focal length of your mirror. Your light source needs to be twice the focal length of your mirror away from the mirror. If you don't know the focal length of your mirror, you can find it like I show in the video, using the flashlight on your phone.
Hey there, awesome video that seems very 'complete' in both theory and practical setup. I was wondering if there would be much advantage/disadvantage in using a laser pointer as your light source? I am guessing you need the beam to be divergent enough to cover the mirror but still coming from as small a point as possible. I may have misunderstood something but as you were using the word laser a lot so I wondered if it was because it would be of benefit to use one if you had it?
Hah, yes I use the word 'laser' a lot because I work with lasers in my research and I'm so used to saying it, so I slipped up a few times in this video! You can definitely use a laser though, and I actually have with my setup. You're correct that you'll need to diverge the beam to cover the mirror. Here's how I did it. I have a simple red laser pointer that you can buy for a couple of bucks. I bought a plano-convex lens to diverge the beam from the laser (search Thorlabs LA1213 on Google, it's the first choice). This happens to diverge the beam just the right amount to cover the mirror in my setup. If it diverges too much, you'll lose intensity, and if it doesn't diverge enough, you won't use all of the usable area of your mirror. I got pretty good results with the laser, but you should note that you'll definitely get a speckle pattern show up in your images. This is just an unavoidable thing that comes with using lasers. I like the pictures I get from my LED better, but if you're using a higher quality or high power laser, it might be better. I say this a lot, but the quality depends on a lot of factors, and it's hard to make sweeping generalizations. You should definitely try it out though, and see for yourself!
HpyCmp3r just a short note about lasers..yes they will work but there a few issues with them. Being a coherent light source, you will struggle to get a very clean field due to the patterns you get, and as they are monochromatic light sources, you will experience greater diffraction around the knife edge. This in turn will make the image a little less sharp. A red laser will be safer here as the wavelengths are far longer. Hope that helps you both.
The problem with using a cylindrical mirror is that you won't get your light source to focus back down to a point. The cylindrical mirrors focus light down in one dimension, but you need to mirror to focus the light down in all dimensions. If you have a point source shining out in all directions at the mirror, then the only rays that will focus back down to the point they originated from will be the rays that hit the mirror perpendicular to the surface, if that makes sense. The other ones will bounce off at the same angle they hit the mirror at, and won't focus back down where you need them to. So what you'll get is probably a single line of light that focuses back down to where you want it, which won't give you anything useful in terms of this setup. If you already have the mirror, try setting it up and see what happens.
The mirror is the key -- but long focal length = expensive. My 6th-grade son is doing a science project on improving shadowgraph and Schlieren sensitivity while keeping costs low. The problems we're finding with the DYI Schlieren videos on TH-cam are either (1) the sensitivity sufficient to see heated air rising from your own body, or seeing your breath, requires a really expensive mirror, and (2) the inexpensive setups can image only really big heat gradients, like plumes coming off flames and soldering irons. We have some ideas we want to try (yes, this has sort of become my science project too), Part of his assignment is to interview someone knowledgeable. Are you willing? By the way, the Novatech MCC106 mirror www.novatech-usa.com/MCC106 is low cost and decent, advertised at 150mm focal length but is actually 120mm. Pretty short, but it works in the "Smartphone Schlieren" article at arxiv.org/pdf/1609.04298.pdf (which I built after the author sent me the STL files, although it's for an iPhone 6 and I had to modify it for my Samsung phone).
Yea, I ran out of room in the video description. To create the point-source, I use a little piece of aluminum foil, and poked a hole in it with a pin or a needle. For the black mask, I bought a piece of black construction paper, and cut a little rectangle out that would fit over the circuit board. Then I cut a small circular hole in it so that I could slide it over the LED.
Josh, can I use this setup for large images, like the air moving around people's bodies as they walk? If yes, I should change the scale of what objects?
Yes, it's possible to do this. With this particular setup, you'd essentially just need a larger diameter mirror. There are other methods/setups that might be better for larger subjects though. One that I'd like to try in the future is Background Oriented Schlieren.
When i attempt to do this set up and test to find the focal point of the mirror using my phone, it ends up being almost directly in front the mirror where that little dot is smallest, is there something that i am doing wrong or is there something wrong with my mirror?
It sounds like your mirror just has a really short focal length. That was the case for the bathroom mirror that I use at the end of the video (although it still had a long enough focal length to get a decent image). You might want to get a mirror with a focal length more like the one I use in this video.
I believe the focal length of my mirror is 75mm is it still possible to do this with such a small length? And also I ordered my mirror from the website in the link Edmund Optics
Yep, that will work. I used my Samsung phone with this setup too and it worked, I just didn't want to make this video longer than it already was. The video is higher quality with the DSLR, but a phone's camera can definitely work. You'll still need a way to make sure it doesn't move, so I ended up buying a little phone mount that attaches to my tripod (for a few dollars).
Can't get access to a nice mirror? Or you want to try something different? Check out my video on Background Oriented Schlieren (BOS): th-cam.com/video/VCUN59x0LF4/w-d-xo.html
What kind of cameras can this work with though? Do I need something fancy, or could I use a phone? if not, then how fancy does one need to get?
@@aether222 You can use your phone without a problem. I would highly recommend putting it on a tripod though. You can get rid of vibrations (as I show in that video), but it's much better if you use a tripod.
@@JoshTheEngineer What did you think of my idea of using computer methods to further enhance optical Schlieren photography? If computers can enhance regular video to show Schlieren so well, surely some method could enhance optical schlieren to make a super sensitive system?! (even if it needs a version that works with brightness or colour not translation).
Wow, great video! Thank you for the detailed explanation. I was going to do some experiments with a less-then-opticaly accurate parabolic mirror and you saved me from a lot of wasted time.
Thank you! I'm glad I could help. As you saw at the end of the video, the bathroom mirror produced pretty poor results, but it did technically work. So it ends up being a trade-off between price and quality. Depending on your application, you could start with something you have lying around, and if it doesn't give you what you want, then a move to a higher optical quality might be a good idea.
thanks for this wonderful video and your comprehensive explanation. we are going to try it!
Good luck!
That's a cool set up! I like that you used a commercial one to show the difference in quality of the image. It made realize i didnt have to get fancy just experiment with this type of photography. It would be a cool experiment to do in a middle school or high school physics class too, for the teachers out there teaching kids about STEM.
Next time you do this, you can try using the spot meter on your camera, your camera will only ready a specific point instead of an area. If you put your nikon on aperature priority, set it to the smallest f/22, with a spot meter (exposure settings (AE, scroll using the wheel, find spot)), you wont have to fiddle around with the exposure compensation as much, or might be able to go darker to get. more contrast which seems key to this type of imaging. Closing your windows would've helped to, your camera wont try to read the ambient light, it would just over expose the experiment.
Thank you for taking the time to make this really in depth video! i am taking a compressible flow class and saw this technique being used for past experiments, did some google searches and found some neat videos, yours by far the best! I am a photographer and engineer so this experiment tickled my fancy haha.
Good work!! =D
Thanks! Yea, this setup is super simple and would make a great display for some STEM outreach. That's been on my list of things to do for a science fair or something, now I just need to find the time.
Good advice regarding the camera settings. I always just default on matrix metering because that's what I mostly use when I'm outside shooting. Unfortunately the blinds on my windows are what they are, and let quite a bit of light in even when they're fully closed (although after looking at my video again, I noticed I didn't even close them). I'll try the small aperture and spot metering next time I set it up. Thanks for the info!
Good luck in your compressible flow class. It was one of my favorites when I took it in undergrad. I actually have quite a few compressible flow videos on my channel if you ever get stuck.
Thanks for this great video. I've been trying to make a schlieren effect set up for quite some time now, but I thought it would require expensive instruments and tools. After seeing this video I made a quick try with a commercial mirror and I guess it will be possible to make it work.
Great tutorial. Thanks for writing out such comprehensive details.
Your explanation of how it works gets the point across better than any other professional schlieren mirror video I've seen.
I think I am going to try this out myself.
Thanks, I appreciate it! There are a lot of other nice videos on TH-cam showing peoples' setups and results (some mentioned in the video description), but I didn't find any that laid out step-by-step how to make a setup at home, so I thought it would help others who wanted to do it themselves.
If you get stuck, feel free to ask me questions.
Fantastic video! Makes me feel like trying out on my own!
Thanks! This is a great little weekend project, and according to my calendar, there's a weekend coming up.
Great info, looking forward to trying this out. Cheers!
I recently discovered Schlieren imaging. I want to build one myself.
There are a few variations that I suggest to you should be investigate.
VARIATION #1
You used a vertical position of the razor blade. How different the image would be if the blade was horizontal? Comparing both images vertical/horizontal razor blade position would be interesting.
Along the same line, how about puting the razor blade a different angular increments and compare the resulting images? For example, you can choose the angular positions of 0, 15, 30, 45, 60, 75, 90, angular degrees.
VARIATION #2
This is something I saw from another TH-cam video. They used colored light filters instead razor blade. This gives a far better result because the image is no longer blocked off, but colored. the resulting image gives far more visual information.
Another similar variation is to use use two colored filters side-by-side in place of the razor blade. This seems to give the best result of all because the surface of the gradient becomes visible at both poles of the gradient.
Another similar variation would be to find a color filter that changes from one color to another. This may be from one color to full transparency. This type of color filter might be harder to find, but they would hold good results because no information about the image would be lost for contrast.
VARIATION #3
Use a polar light filter instead of the razor blade. You can use the polar light filter in the cheap 3D glasses given in movie theaters when they show 3D projection movies. Polar filters have a direction up/down or left/right. You can experiment with that in the same way as with the razor blade. First you try one filter replacing the razor blade and see what the result is. The filter might block off too much light and acting like a razon blade. Then you can try two polar filters side-by-side with one having vertical polar direction and the other having horizontal direction. I imaging that the light intensity might have to be increased significantly.
Succes! I got clear picture with a small flame
thank you
Awesome! Glad I could help out.
TH-cam will always amaze me...
Why when i search for videos like this, i only find "crappy" ones or others that have nearly to information or details, only to get recommended videos like this and it is almost a decade old.
Why can't i find them on my own ffs?!
Thank you for making this video.
No problem!
This is a great video, thanks a lot! I'll try to make a similar setup for teaching optics (and convection) at the local polytechnic museum.
You're welcome! That sounds like a great idea...good luck, and let me know if you run into any problems.
that is fantastic ! thank you so much
Thanks for watching!
Oh, thank you so much. I was trying to make Schlierenfotographie for years and at all the sites were I have been everybody talks about putting the camera at 2f. So it never worked. Your video gave me the clue needed that it must sit on 1f. So obvious. I thought I messed up some other component.
Now it works.
Do you think that one can observe smaller differences in refractiv index of the fluids with better optics?
You're welcome! I just want to make clear here though that in this double-pass (single mirror) system, the light source and knife edge are in fact located at 2f. That is, two times the focal length of the spherical concave mirror. A better mirror is the easiest (though probably the most expensive) way to get better images. You can also change sensitivity with the knife edge. It will also depend on the size of your light source and the tightness of the focused spot.
Cool vid! Is this gonna be the start of a DIY series? Or is it a one hit wonder.
+mikehalloran93
There will most certainly be more DIY videos; I'm no Natalie Imbruglia. Get it?! You'll get there eventually.
you might be able to sell pre prepared sets? nicely fixed lens holders and the correct distances etc :)
Hah, that would be nice! I've been 3D printing some parts for this setup, so when I get all the kinks out, I'll make those files available.
that is even more humane, wow im surprised. im like that myself, did not expect that :D i just share it and seed ideas into the world. still, for peoiple without acces to a 3d printer, you could offer a starter kit :d well balanced etc, or a little booklet i dont know :D keep up the awesome work!
do you often engineer projects etc? im working on a 3D ufo model that i think could work, like a drone only everything doubled in xyz like rotors on top and below working in tandem. im looking for someone with engineering experience for a few pointers perhaps. :0 some one who likes to help save this world :)
Hello! I was wondering if why we need a small light source. What happens if we use a larger light source?
Thx for your video, it helped me a lot in understanding Schlieren photography.
the result wont be as focused, so you'd get smaller quality of shclieren effect
"Only one thing I couldn't figure out. What's a radio shack?" -next gen nerd.
Jake Meyer
Lol seriously ?? Hahaha .. you know .. c'mon .. u r funny ..
Super video, thanks so much!
No problem!
Who's here from after watching veritasium? Great tutorial Josh , thank you :)
Yea, Derek had a pretty cool setup going. It also helps having a big mirror! Thanks for watching!
me,
I actual got it to work from a cheap mirror
Veritasium just posted a new video on schlieren
amazzzzzzzzzzzzzing.. and really loved it.. I would try to buy some good quality mirror.. but did you try this with even more easy using MOBILE's Camera with manual focus or something?
Yea, I tried it with both an old digital camera and my phone's camera. Both worked, but the quality was obviously lower than using my DSLR.
if the LED is placed at 2f position and the viewing angle of the LED is too large does that mean not all of the reaches the mirror and being reflected? if thats the case does that mean i need to use the tangent formula and calculate the half angle of the LED to choose the most appropriate one?
Kudos... well done.
A question: if you wanted to capture a sneeze or breath, let’s say an area a little bigger than a head, that would require a mirror of maybe say 12-15 inches. Obviously a quality scientific mirror would get pricey... any suggestion for an “adequate” solution? Perhaps a solar capture plastic mirror? Obviously not “fine”, but perhaps better than the cosmetic mirror.
Again, this is a well done demonstration. I showed it my son in law, his response was two simple words... “mind blown”.😉
Thanks! Yes, mirrors can get quite expensive, especially nice ones that you need for schlieren measurements. One method that doesn't need a mirror is called background oriented schlieren (BOS). I recently made a video going through an entire DIY setup that might interest you (th-cam.com/video/VCUN59x0LF4/w-d-xo.html). You might have some trouble getting it to be as sensitive as a conventional schlieren setup, but this recent video by LaVision shows how sensitive it can be (th-cam.com/video/kYJvU81DKgk/w-d-xo.html&feature=emb_title). Note that LaVision is a company dedicated to flow diagnostics/visualization/imaging, so what they show is going to be hard to achieve at home with a simplified setup, but you can get pretty close.
+JoshTheEngineer do you think it will work if 1 foot behind the razor blade we placed a white paper as a screen so we get the image? I mean not to use a camera
That should also work, since the camera is mainly there so you can record images or videos. You might also notice that if you take the razor blade out of the setup, you can place a piece of paper where your camera would generally be, and you should still be able to see something that looks like Schlieren, but is actually called shadowgraph.
shadowgram yes
Holy smokes dude. I had the 2¢ version of how Schlieren imaging worked before I searched the term and found your video, and by the 1:38 mark you've made it clear the whole trick is the same interaction between point source light and atmosphere that makes stars "twinkle," and described how to recreate it consistently over a variable distance. That's the whole answer to how to build one, but I'mma still watch the rest of the whole video out of respect and expect to learn a hell of a lot more.
(Edit: mild dysgraphic moment)
Great work Josh! I have a question tho... why is it better to use a spherical mirror instead of a parabolic one? Since parabolic mirror focus collimated light without introducing spherical aberration I fail to understand why shperical mirror is the best choice. Cheers
Thanks! The spherical mirror is needed for the double-pass schlieren system, whereas the parabolic is needed for the Z-type schlieren system. The one I show in this video is the double-pass, and only requires one mirror. I'll probably make a video on the Z-type system at some point, but it requires two mirrors. You're right that the parabolic mirror collimates the beam, but we actually don't want any collimation for the double-pass method. The spherical mirror is used because if you locate you point source twice the focal distance from the mirror, it will reflect off the spherical mirror and focus back down at the same 2f distance, which is then where we place the knife-edge. For the Z-type system, you place the point source at the focal length of the parabolic mirror, which then collimates the beam, and then a second parabolic mirror takes that collimated beam and focuses it down at one focal length, which is where we place the knife-edge. There are pros and cons to both types of systems, but that's the reasoning for the different mirrors.
Is it possible to see inaudible frequencies that are being broadcast into a house? I am seeking a way to trace their origin. I would really appreciate any information or advice you could give me. Thank you for your video. Very well done!
Thank you! The sensitivity is realistically going to be too low to see those sound waves, but there are certain instances where you can see them, for instance when you set up a standing wave. There are some demonstrations of schlieren being used for sound wave visualization that you can take a look at (by the Harvard Natural Sciences Lecture Demonstrations).
Many thanks for very good explanations :-)
My pleasure!
Thank you! I will build a set and put the final result on my tranparent paper paravant which seperates my private space from my working space. Customers will see the result but not the setup. THANK YOU!
Sounds pretty cool! Good luck!
WHAT A NICE VIDEO!!!!
but,I think in this system the light has passed the Density variation region twice， I think，it will has some infulence for this system。
Thanks! Yes, in this setup with only one mirror, the light passes through on the way to the mirror, and then again on its way back to the camera. A Z-type system is a little more straightforward in that the light only passes through the region of interest once, but you also need to buy an extra mirror.
Great explanations
Thank you very much!
Hello josh, I'm 15 and I from France, in high school we have to do a project in groupe of 2 or 3 about the topic we want and the final mark of this project count for the baccalaureate. So I think that in our project we will do this experience : first we'll put a brick behind a ventilator, then we'll put a little car (a toys) behind the ventilator. thanks to your tuto, we will be able to see what will do the air and we will be able to compare the effect of the ventilator's air on the two objects and the effect of the objects on the ventilator's air. Could you tell me If you think it's a good or a bad idea? I don't know if you managed to understand what I mean so I'm sorry if you don't. Thank you a lot for your video !
it work! thank you!
Hi thank you for this great video! If I don't want to buy a camera, can I use my iPhone camera instead?
Thanks! And yes, absolutely. Back when made this video I had taken some images with my Samsung phone and it worked just fine. You'll have more control with a dedicated camera, but you'll absolutely be able to get nice images/videos with your phone.
your video which i looking for .
thanks .
and i have subscribe your channel
Thanks, I appreciate it!
I've gotten decent results with just using a large magnifying glass instead of mirror
Fantastic experiment! It is possible to se the effect with eye without camera? Thank you!
Yep! You can just take out the camera and hold up a piece of paper a little farther back behind where the camera was. The farther you move the paper back, the larger the image gets, but it will also get dimmer. However, you'll be able to see the effect no problem. Note that the image will be upside down. You can also switch between Schlieren and shadowgraph by pulling out the knife edge.
I Try to set up the system .
1,And I do some change ,the angle of this system is bigger. I see the candle and the candle in the mirror.both of them have the shadow.
2.I analysis the image by matlab and i find one half image is dark a little . I think it in relation to the knife cut the focus .
To make sure you get the best image in the end, I recommend leaving out the knife edge until you can see that you get nice uniform light all across the mirror. If the light is uniform over the mirror, that means you have a good quality mirror, and your camera is aligned in a good location to then put the knife edge in.
The next step is then to put the knife edge in before you put the candle in. You should still have a uniform distribution of light on your mirror, but it will be a little dimmer because you're cutting out some of the light. Finally, you can put the candle next to the mirror, and you should get some nice images.
If you put electrical tape on your circuit board. You will be able to place the razor blade anywhere under the board.
@ JoshThe Engineer : I have seen this effect many, many times in the shadow of my car's hot roof. Also, I see it sometimes on the wall of my bathtub when there is a hot bath.
How are these situations working?
Also, I wanted to ask how that NASA used this technique on a full size aircraft to show the shockwaves.
I had never seen this technique used on anything but small objects in a lab environment.
I skimmed the article, but will continue to research how they did it.
I'd love to be able to use the technique to visualize the airflow around my car.
www.nasa.gov/centers/armstrong/features/supersonic-shockwave-interaction.html
They use a method called Background Oriented Schlieren. I actually made a video about how you can use this method at home, and I provide some simple code that will help you process your data:
th-cam.com/video/VCUN59x0LF4/w-d-xo.html
The NASA data from those now-famous pictures was taken from a plane flying above the target plane, and looking down at the desert floor. You can also take these large-scale images by pointing your camera at the sun and using an appropriate filter (I wouldn't try this one at home as a beginner, but you'll find papers on it). Maybe I'll make another video where I go into more detail about their measurements, but my video at least shows you how you can do it at home. Hope that helps!
@@JoshTheEngineer Thank you ! I saw other videos where the planes fly in front of the Sun, but this image puzzled me, because the planes in this instance were seen from above.
I assumed maybe they were just superimposed in Photoshop . Thanks for clearing that up about the bright desert floor. Your video is absolutely, just the thing I was looking for!
I will be sure to watch it in it's entirety later.
Thank you for posting!
I think opticsplanet sells similar mirrors on ebay with a bit higher prices
I'll have to check them out. Thanks for the reference.
Thanks a lot for your video! I am from Colombia and probably I wouldn't do it without this explanation!
Glad I could help!
This was great! I finally know how to make one of these. Now I just got to find a good reason to make one...
Nice thank you very much
Will a parabolic mirror work? I have an 8" in my telescope.
While the optimal mirror for this double-pass system is a spherical concave mirror, a parabolic mirror will still work okay. For the Z-type (two-mirror) schlieren system, the parabolic mirror is the optimal choice. I'm currently filming a spherical vs. parabolic mirror comparison for schlieren systems where I'll go over why you can use either, but also how performance is degraded depending on which system you're using it in. I'm also editing a Z-type schlieren system video, so if you have two telescope parabolic mirrors, you can get some really nice images from that system.
Thanks for making this video. I saw the Schlieren effect in a pilot training film describing how moving air causes lift in an aircraft wing. That was in 1967, and I never forgot it. I also never saw it again until I stumbled onto your video. Thanks again!
Thanks man, I've passed my project because of you.
Awesome to hear!
Can you explain what is focal length?
Does it work if you don't use a point source, but instead use a light source that produces beams parallel to the principal axis of the mirror, and place the blade edge and camera at the exact focal length instead of twice the focal length?
That's actually sorta what the Z-type Schlieren system does. You're essentially just skipping the first mirror part, which collimates a beam from a point source located at the focal point of a parabolic mirror. Then after the collimated beam passes through the region of interest, another parabolic mirror focuses the light rays down to a focus, where a knife edge is located, and then into your camera.
Amazing video.
I have a quick question, if you have the time.
What is the minimum temperature difference that can be shown in this setup?
Can heat rising from a human body be shown like this?
Thanks very much.
I will be as brief as possible. ONE the presentation if complete, that is numbers, calculus, formula, and subsequent derivatives thereof. Thank you so much for this great chance at a little know idea/subject! YET, again, let me say the math, means and hows to make such a LANDMARK devise is not done by too many (no doubt due to the guys like me that are gonna ask for necessary improvements...), WHAT, please is the absolute (as pragmatic for homebuilders like me and you ) diameter of that "PIN HOLE." I built the devise, but it doesn't work. Indeed my entire
set up was due to an incorrect "pin hole" in that foil over the
LED. Thanks again, in the name of DIY and the movements like demonstrating a "better way" sense 2000 pt Secret name of Most High.
I know this sounds ridiculous, but if one cannot get a precision mirror. Take lots of math and time, but give cheapo mirror aprox. 3k spin (or more RPMS) theoretically, this should account for those imperfections in your mirror from the drug store. Again, lots of time AND math to get a parallel mirror "perfectly" spinning around, but yeah the imperfections "melt" together, while the mirrored light is concave. This is said in lieu of the movements and all the utterances to live by sense the 2020 Paradigm Shift. Thanks again. If I'm wrong, I'll Eat my fricken plastic enhanced coffee cream!
Hi! I believe I have everything needed at home. The mirror is one of those that you put in the bathroom I hope it'll work!
I'll find a razor blade somewhere in the house and there must be a LED lying around as well.
My only problem is that my camera is a semi-DSLR?(if there's such a thing ahah) By that I mean you can't zoom in and out manually and you can't really adjust the exposure. Will it work in a super dark room? I'll try to cover any lights or maybe put a long cardboard box between the camera and the mirror. I don't know, if you have any suggestions please help me! This project looks so cool
help me maybe?
Hello! The mirror I use at the end of the video is a bathroom mirror, so you can see that maybe you won't get the crystal clear images like I get with my good mirror, but you should still be able to get something. If you don't have a razor blade lying around, you can always use a knife, just be careful. You can use any light source, even a light bulb, as long as you put a cover over it and poke a little hole in that cover to make a quasi-point source.
I've gotten good results with my DSLR, my point-and-shoot circa 2005, and with my phone. The main problem you'll run into is that you won't be able to zoom in on the mirror, so it might be sort of small on your screen or in you picture you take. That's the problem I have, since I don't have a lens that zooms far enough. Your camera should definitely have some sort of exposure setting. All three cameras I just mentioned have the option to adjust the exposure manually, even my phone. I would just check the manual for the camera. It's easier if the room is dark, but as you can see in my video, I'm taking this video during the day, so that should work just fine too. Good luck!
Great video! interesting, very well done and easy to understand.
I'm glad you liked it! Thanks for the positive feedback.
Hi! I'm a high school student in korea and I have a question. If light rays bend as the air density changes, then does it mean that light always bends because the density of the light always changes?I went to this site goo.gl/gI1YQq where you recommanded to all viewers. And the question just popped up! Please answer my question if possible.
Gr8. And thanks 😊
Off topic but your voice exactly matches your face.
I've been waiting for someone to tell me this my entire life, but it always seemed like a weird question to ask.
Hello Josh, I have a stupid question for you concerning night vision cameras ??? Since the camera uses infrared light to enhance the light around the lens this can easily be seen with an app on a smartphone. This defeats the purpose of in cognito of the camera in the first place. What can I do to be able to film what is going on to about 400 feet distance with good resolution ??? Is there something you can be kind enough to guide me in the right direction if there is something out there in the field with a reasonable price ???? Thanks a bunch and peace.
Your video is very well done with the right ratio of information and whiteboard illustrations. Thanks a bunch and peace too.
Thanks for this
Thanks for your explanation...❤❤❤
You're welcome!
Great demo! Could you now make a DIY supersonic wind tunnel to watch some shock waves?!
+joemonster55
That sounds like something that I would definitely be interested in doing (i.e, make a shock tube with a little viewport and a place to insert a mini model). However, this will take some more time to think about and execute. I do have some other interesting ideas about how to use this setup to visualize shock waves from bullets, etc.
I will probably post a couple more videos describing minor perturbations to this setup first, such as using the external camera flash instead of the LED. But if you have any cool ideas, let me know!
+JoshTheEngineer I would also be interested in a DIY video of a shocktube to see some shockwave (If the cost can be kept down like we see in this video). Can a simple paintball gun produce a supersonic shockwave if we fire it into low pressure air?
The shock tube idea is definitely still on my to-do list for the future. I have so many other videos I'm trying to work through at the moment, but I'm going through some calculations for a shock tube design that would result in shocks strong enough to be seen by a simple Schlieren system like I showed in this video.
I also wanted to do a video on Schlieren images for some sort of gun or projectile launcher, so that's in the works as well. I would have to look more into paintball gun firing velocities, but I can guarantee that you would see something coming out of the front. What you see and with how much sensitivity will be dependent on the gun characteristics and the sensitivity of the Schlieren setup (focal length, mirror quality, light uniform-ness, and so on).
Hi. We're trying to make a Schlieren set up for our research. And we want to use a 50 cm Diameter mirror. We'll be making our own mirror using space blankets. Is it possible that we can still get images???
I think you'll definitely get something, though I'm not sure what kind of quality it will be. I had wanted to try this setup with the mirrors that NightHawkInLight made, so let me know how they work!
But there is no Radio Shack :-)
Ha, yes you can tell this video is a little dated.
I have been trying to get this to work for a few days now. I am using a DSLR camera, a concave mirror with a 24" focal length and a razor blade setup just as yours is in this video. I am getting to a point where the mirror appears gray-ish, like in this video. However when I turn any heat source on in front of the mirror, nothing shows up in the image. Any tips? I have tried a couple different light sources including an LED flashlight with the reflector taken out and a black cover over the top with a hole in it and an LED point source like yours in the video.
I'm assuming you've pretty much set up everything the way I do it in the video, so let's work through a couple scenarios and see if that helps. If you remove the knife edge completely from your system (and you don't put anything in the beam path, which I'll just call a candle from now on for simplicity), you should get a uniform light distribution on your mirror as viewed through your camera. If you do, that's a good first step.
The next thing to do is to place the knife-edge in the beam path, at the point where the beam focuses down to a point, still without the candle. If you cover up half the beam with the knife-edge (you'll see half the beam spot on the knife-edge, even though it'll be small), then you should see your intensity go down, but it will still be uniform. The more you move your knife-edge into the beam, the dimmer the image on your camera will get, but it will always stay uniformly lit. After the knife-edge blocks the beam, you obviously won't see any light passing through to your camera.
If everything makes sense up to now and is working like I mentioned, then you should bring the knife-edge back to the point where it's covering about half the beam spot at the focus. As we saw before, you'll have a uniformly lit mirror, but it will be dimmer than if there were no knife-edge in. No place your candle as close to the mirror as you can without it burning or heating up the mirror, maybe an inch away. You should see something now on the camera. If you pull the knife-edge out of the beam path slowly, then you'll see the sensitivity decrease, and the mirror will become uniformly lit at the full intensity of the light source. If you move the knife-edge farther into the beam spot, you'll still "see the heat", but the background intensity will go down. If you look at the video that the TH-camr "brusspup" posted, you can see in that setup that he has most of the beam spot covered by the knife-edge, which is why the background looks so dull and gray. I personally don't like the way that looks, so I usually do about 50% coverage, and then adjust back and forth until I get an image I like.
A couple of other things to note. Orientation of the knife-edge does matter. If you're looking for horizontal gradients of index of refraction, then you need to orient the knife-edge vertically, as I do in the video. If you are looking for vertical gradients of index of refraction, then you need to orient the knife-edge horizontally. Or you can do it at an angle and be slightly sensitive to both. For a candle, put the knife-edge in vertically because the index of refraction changes abruptly in the horizontal direction. Also make sure that your return beam spot is coming back as close to the LED source as possible (within reason). This will eliminate double images. You might need to adjust your exposure compensation on the camera too, because as you can see in my video when I bring it back to 0 (no compensation), you can't see much on the mirror. Another TH-cam comment mentioned that I could have used spot metering as opposed to matrix metering for my exposure, where the spot would be fixed on the mirror such that it was correctly exposed for the mirror light.
Hope something in this response helps with your setup! If it does, let me know what fixed it.
Where I can find a Spherical concave mirror less than $50?
I have two meade LX telescopes that have nice mirrors but failed electronics. An 8 and a 12 inch. Nice basement to set it up in for the distance. Time to get busy!
Sounds great! You can also try a Z setup with two mirrors.
Hi Josh, I tried to set up my 8 inch Meade SCT last night. I took the corrector off along with the secondary mirror. They aren't suited for this. The focal point of the primary mirror is 16 inches where it is folded by the secondary into a baffle toward the visual back. The mirror also has a good sized hole to fit the baffle. I had considered it would be a problem way before starting but played with it anyway. Any ideas? I did notice if I place a bright LED flashlight smack in front at 16" I get a focal point across the room on the far wall. Unless I am confused. I thought you were focusing on a pinpoint with your camera. I'm not clear how you could resolve that tiny point into something useful. I'll watch it again.
I figured it out.
I managed some butane. I did not use the blade to block light. Maybe the camera was offset enough. Actually I was almost 2X distant from the light source focal point. th-cam.com/video/2BSEaf9Atro/w-d-xo.html
Thank you for your post! This is the best video I have ever seen about Schlieren-Shadow imaging. I successfully built a mini one with a concave mirror that has a f=50 mm. Most of the parts of mine were 3d printed. I can see hot air, butane and helium. But argon, not really. The mirror I used was a scientific grade concave mirror with aluminum sputtered for UV. Also I used green LED instead of a white one due to the fact that refraction of light is positively related to wave length. I think a blue one might work better.
One quick question, have you thought about build one with 2 concave mirrors? That should give you "True" Schlieren imaging and better sensitivity. BTW, I don't think the focal distance is the major factor that determines the sensitivity or image quality. Instead, I think the quality of the pin-hole and the razor blade are the keys. Please correct me if I am wrong about it.
Thanks again for you post!
Thanks for watching; sounds like you have a pretty cool little setup! I definitely want to make a 2-mirror Schlieren setup at some point, but the reason for making this one is that it is the cheapest for the frugal DIY-er. It's also pretty easy to construct and align everything. I'll probably get around to make a more scientific setup at some point.
There are a lot of different aspects of the system that affect the sensitivity. I mentioned the mirror as (arguably) the most important component because of the uniformity of light that we see in the images. If the mirror is poorly constructed, you'll get some dark spots, and the light source won't focus back to a perfect point. This then makes the razor blade placement a little tricky.
I do think that the focal length is important for sensitivity because if you think of the divergence of the ray from it's nominal (non-refracted) path, the longer the focal length is, the farther the displacement from its final location it will be when it gets to the 2f distance. This makes it more sensitive to pick up lower density gradients. However, like you mention, knife-edge placement is also key. You can pick up different gradient directions by aligning the knife-edge vertically, horizontally, etc. You can also block all the undisturbed light as well by making sure the knife-edge covers the center of the beam, and then you'll only see the refracted light. There are a lot of different opportunities with regard to the knife-edge design and placement that will affect what you see in the image or video.
So it really ends up being a combination of many components that influences the sensitivity and images you see, and it's hard for me to confidently say that this one component matters more than that one without getting into some more advanced optics equations.
Hey Josh, Thanks for the video. I have a question by the way. I saw your reply to one of the comments below, where you mentioned that the first step in Schlieren is getting a uniformly lit mirror. What exactly needs to be done to achieve this? I am using an 8" dia, 30" focal length mirror with a Nikon D610 for visualization. I can visualize the flow patterns, but my mirror is not uniformly lit and the image is just focussed on a small portion of the mirror. What should I do to get it over the whole mirror?
No problem! The easiest way to get a uniformly lit mirror is to take out the knife-edge completely, and place your camera (behind the point where the light focuses back down to a point) in a location where you see the mirror completely filled. You've probably tried this already, so here are two more things to check.
First, make sure your light source is diverging enough such that it completely fills the mirror. As an extreme example, if you use a laser point without a diverging lens, the light spot you'll see in your camera will only be as big as the laser beam diameter. You can see in my Laser Schlieren video (th-cam.com/video/JvHZT_wBpUE/w-d-xo.html) that when I use a diverging lens, the light overfills my mirror a little bit, which is better than it under-filling the mirror.
Second, make sure your aperture (F-stop) is open as wide as it can go (lower numbers). I was trying to take some high speed Schlieren a little while ago, and it turns out I couldn't attach my lens of choice to the camera because it would auto-adjust the F-stop to the smallest aperture (highest number). I had to use a manual-aperture lens with that body so that I could make sure the lens was wide open, which didn't restrict the light entering the camera. Try checking this, and let me know if it doesn't solve the problem.
12:45 look at the arrow of light a few inches from the mirror, watch how it stretches out and disappears right as he reaches the focal point. Does anybody know what that is or how the camera can see it?
Thanks Josh, awesome video with great explanation. I have a question, would placing the light source and knife edge at the focal point work as well? since at focal point the light will also come back as a dot just similar to 2f point. Also, is the led bulb collimated? Does the light source need to be collimated? Thank you!
You're welcome! If you placed the light source at the focal point, the light would actually leave the mirrors collimated, and wouldn't focus back down again. This is actually what the Z-type Schlieren system does. You place the light at the focal point, collimate it with a mirror, then use another mirror to focus the collimated light back down to a point at the second mirror's focal point, which is where you would place your knife edge. This way, you get collimated light through your object of interest. The LED is not collimated; it emits light in all directions. You don't want a collimated light source, because it needs to diverge out to fill the mirror. Lasers are collimated, which is why in my other Laser Schlieren video, I use a lens to diverge the light so it encompasses the mirror.
Thanks, Josh! I thought it's just a good video, but when I saw that mirror stand made from cardboard and adhesive tape, I instantly clicked on "subscribe". DIY in its purest form. Love it!
You're welcome! Sometimes you just have to use what you have lying around.
Cool video. To show the turbulence caused by the heat of the candle it is better to have the candle several centimeters below the center of the mirror. The column of rising air above the candle is laminar for a few centimeters then transitions to turbulent flow. The turbulent flow is more interesting to watch.
Thanks. You're correct, I could have moved the mirror up a little. However, showing the laminar part is a good way to show how the knife-edge affects the results you're seeing. I didn't switch the knife-edge in this video, but it would have been a good explanation to rotate it 90 degrees, and show that you don't see any gradients.
im sure you probably know XD but all radioshacks are closed now, is there anywhere else you suggest getting the LED and if so what specs LED did you use??
Yea, unfortunately they were starting to go out of business when I made this video. If I were you I would just buy a pack of LEDs off of Amazon. You can get a bunch of them for pretty cheap. I just used the standard 5 mm clear LED, but you can honestly use whatever kind you want.
Why is it 2f? I thought the focal length is the length that everything gets focused down at?
hello, I don't get why you need a sharp metal thing, would it be possible to do it using a plastic materials?
You need something sharp/straight so that it has a well defined edge to cut off the light. You also need it to be thin (axially along the beam path) because if it's too thick, it will get in the way of the beam as it's focusing down to the point. A razor blade just happens to satisfy both of these limitations, and they're inexpensive. You should try it with a different object, and see how that changes your results!
Does it give more clear picture because distortion happens, twice, once going towards mirror, once light returning from mirror ?
The double-pass nature of this particular setup makes it more sensitive to distortions. So it's really the sensitivity that's increased, not necessarily the clarity of the picture/video.
Wait did he say radio shack?
I sure did!
Question, does it show magnetic fields?
@Klarname Mustermann lol
Thanks for putting this together. I'm sure it was a lot of work - but for us the viewer. Totally Awesome! Thanks
I enjoyed doing it, and I'm glad it was helpful!
❤👍
Very nice! For years, I have thought about this kind of imaging and not known how they are made and finally I know and would even be able to do it myself if I like to. Many thanks!
You're welcome! It seems like a lot of other people in the comments have had success with their own setups, so you should definitely try it yourself!
Incredible video! Every step is so well explained :) Subscribed right away!
Thank you!
i can place the setup further than 2ft? does the light - camera distance matter and how could i calculate it?
The separation distance between the light source and mirror is dictated by the focal length of your mirror. Your light source needs to be twice the focal length of your mirror away from the mirror. If you don't know the focal length of your mirror, you can find it like I show in the video, using the flashlight on your phone.
Hey there, awesome video that seems very 'complete' in both theory and practical setup. I was wondering if there would be much advantage/disadvantage in using a laser pointer as your light source? I am guessing you need the beam to be divergent enough to cover the mirror but still coming from as small a point as possible. I may have misunderstood something but as you were using the word laser a lot so I wondered if it was because it would be of benefit to use one if you had it?
Hah, yes I use the word 'laser' a lot because I work with lasers in my research and I'm so used to saying it, so I slipped up a few times in this video! You can definitely use a laser though, and I actually have with my setup. You're correct that you'll need to diverge the beam to cover the mirror. Here's how I did it. I have a simple red laser pointer that you can buy for a couple of bucks. I bought a plano-convex lens to diverge the beam from the laser (search Thorlabs LA1213 on Google, it's the first choice). This happens to diverge the beam just the right amount to cover the mirror in my setup. If it diverges too much, you'll lose intensity, and if it doesn't diverge enough, you won't use all of the usable area of your mirror. I got pretty good results with the laser, but you should note that you'll definitely get a speckle pattern show up in your images. This is just an unavoidable thing that comes with using lasers. I like the pictures I get from my LED better, but if you're using a higher quality or high power laser, it might be better. I say this a lot, but the quality depends on a lot of factors, and it's hard to make sweeping generalizations. You should definitely try it out though, and see for yourself!
HpyCmp3r just a short note about lasers..yes they will work but there a few issues with them. Being a coherent light source, you will struggle to get a very clean field due to the patterns you get, and as they are monochromatic light sources, you will experience greater diffraction around the knife edge. This in turn will make the image a little less sharp. A red laser will be safer here as the wavelengths are far longer. Hope that helps you both.
Thanks bro, for this explanation!
Hail from Russia!
You're welcome, and hello!
learned a lot from this. Really nicely explained. Watching the vibrations of you walking is cool.
Thanks! Yea, the vibrations show just how sensitive the positioning is. I was actually trying to walk carefully/quietly, but I clearly failed.
Awesome sir .....its truly Amazing ........i am gonna try today !!!
thanks a lot !!
Glad I could help. Good luck!
Instead of a spherical mirror, can I use a cylindrical mirror? Thanks
The problem with using a cylindrical mirror is that you won't get your light source to focus back down to a point. The cylindrical mirrors focus light down in one dimension, but you need to mirror to focus the light down in all dimensions. If you have a point source shining out in all directions at the mirror, then the only rays that will focus back down to the point they originated from will be the rays that hit the mirror perpendicular to the surface, if that makes sense. The other ones will bounce off at the same angle they hit the mirror at, and won't focus back down where you need them to. So what you'll get is probably a single line of light that focuses back down to where you want it, which won't give you anything useful in terms of this setup. If you already have the mirror, try setting it up and see what happens.
The mirror is the key -- but long focal length = expensive. My 6th-grade son is doing a science project on improving shadowgraph and Schlieren sensitivity while keeping costs low. The problems we're finding with the DYI Schlieren videos on TH-cam are either (1) the sensitivity sufficient to see heated air rising from your own body, or seeing your breath, requires a really expensive mirror, and (2) the inexpensive setups can image only really big heat gradients, like plumes coming off flames and soldering irons. We have some ideas we want to try (yes, this has sort of become my science project too), Part of his assignment is to interview someone knowledgeable. Are you willing?
By the way, the Novatech MCC106 mirror www.novatech-usa.com/MCC106 is low cost and decent, advertised at 150mm focal length but is actually 120mm. Pretty short, but it works in the "Smartphone Schlieren" article at arxiv.org/pdf/1609.04298.pdf (which I built after the author sent me the STL files, although it's for an iPhone 6 and I had to modify it for my Samsung phone).
Thanks for the links! The information was helpful.
Thanks for this great video. I was just trying to quickly find out what Schlieren imaging was, but ended up watching to the end !
You're welcome! And thanks for sticking it out to the end; I know it's a long video.
HI, actually what is the led mask?...i did not see at the details part...
Yea, I ran out of room in the video description. To create the point-source, I use a little piece of aluminum foil, and poked a hole in it with a pin or a needle. For the black mask, I bought a piece of black construction paper, and cut a little rectangle out that would fit over the circuit board. Then I cut a small circular hole in it so that I could slide it over the LED.
Does it also work with a magnifying glass?
That is Awesome!! I think I'm going to make one!! Thanks
No problem. Good luck!
9:03 define "super cheap".
Less than a dollar.
You sounded a bit like Bill Wurtz at the beginning:D
Hah, yea I can hear that. A little bit dry, but that's ok!
Josh, can I use this setup for large images, like the air moving around people's bodies as they walk? If yes, I should change the scale of what objects?
Yes, it's possible to do this. With this particular setup, you'd essentially just need a larger diameter mirror. There are other methods/setups that might be better for larger subjects though. One that I'd like to try in the future is Background Oriented Schlieren.
Thanks Josh!
You're welcome!
Can I use a laser source instead of LED?
When i attempt to do this set up and test to find the focal point of the mirror using my phone, it ends up being almost directly in front the mirror where that little dot is smallest, is there something that i am doing wrong or is there something wrong with my mirror?
It sounds like your mirror just has a really short focal length. That was the case for the bathroom mirror that I use at the end of the video (although it still had a long enough focal length to get a decent image). You might want to get a mirror with a focal length more like the one I use in this video.
I believe the focal length of my mirror is 75mm is it still possible to do this with such a small length? And also I ordered my mirror from the website in the link Edmund Optics
+JoshTheEngineer Can we use the camera of a mobile phone? I mean instead of a special camera? Does it usually work?
Yep, that will work. I used my Samsung phone with this setup too and it worked, I just didn't want to make this video longer than it already was. The video is higher quality with the DSLR, but a phone's camera can definitely work. You'll still need a way to make sure it doesn't move, so I ended up buying a little phone mount that attaches to my tripod (for a few dollars).