Making a Mirror with a Variable Surface Shape
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- เผยแพร่เมื่อ 1 มิ.ย. 2024
- Some concepts in this video have been pictured in a somewhat simplified manner to make it more accessible to a less specialized audience.
Contents:
00:00 General intro
00:56 Conic constant explained
10:00 Explanation of the manufacturing process
12:25 Testing the mirror
15:32 interferometric evaluation using DFTfringe
Additional info on clips/subjects featured in this video (in the order of appearance):
The fire clips were taken from the news site regio14.nl: • Enorme vlammenzee bij ...
The short clip of (Ralph) grinding a telescope mirror is taken from: • 20121027123510 1
The "mirror test" for animals actually has little to do with optics: en.wikipedia.org/wiki/Mirror_...
If you want a more detailed story on conics: www.telescope-optics.net/coni.... Telescope-optics.net is a great source for theory on optics.
Clip of making the ellipse using a rope demonstrating constant path length is taken from the following video: • Ellipse (string and op...
Astroforum link to 610mm flex mirror by forum user Firstlight (in Dutch): www.astroforum.nl/forum/instr...
Document with a description of how to making a "Ceravolo" type interferometer yourslf: www.ceravolo.com/Interferometr...
Links to DFTfringe software:
interferometry groups: groups.io/g/Interferometry. In this community Dale Eason answers all the questions on technical subjects about the software.
Download the latest version of DFTfringe here: github.com/githubdoe/DFTFring...
DFTfringe walk through, displaying most of the basic functionality:
• DFTFringe quick start ...
With the interferometric tests I considered astigmatism in the mirror and only left the following zernike coefficients unticked:
Piston X-tilt, Ytilt, Defocus, Xcoma, Ycoma. - วิทยาศาสตร์และเทคโนโลยี
I consider this video a success.
My brain melted after the 8:35 mark... Holy f..., even more information and better explained then 3 blue 1 brown. (r/unpopularopinion)
Math is so beautiful!!
Lithographer at ASML here. I'm working in imaging but studying about optics design when I found out about your channel. It really helps stuff fall into place for me! Keep it up! :)
I knew Dr Huygens videos are like smoke signals, attracting other uber-geniuses w sprawling knowledge.
Most are probably laymen, like me. Doing our best to follow (even w above avg levels of scientific literacy)
But optics requires scientific-polymaths; deep knowledge of physics, engineering, math, QED, & creativity.
Came for optical facts, got some bird facts. Not disappointed.
Came for optical facts, I got an insight about complex numbers.
At the contents you should have put also "3:15 Spying lady on the window". Nice sense of humor :)
Found through Hackaday. Had no idea someone who specialized in Optical grinding had a TH-cam channel. This is utterly brilliant and I am thoroughly impressed. I have done some Optical grinding at a very simple level to create custom pocket watch crystals because I'm a horologist, among other things. Subbed hard!
I judge how well someone knows a subject by how well they can make me understand it in a short explanation. By this metric this guy is a fucking genius!
The ability to convey complex subjects in a widely digestible form is as much a skill as it is an art and is only refined over years of conversations on the topic.
Also, I agree! Absolute legendary channel for quantifying optics and optical quality!
8:43 this gave me an insight into complex number, "its beyond the scope of the video" sure it is, thank you.
You find answers to hard problems in the strangest places. I've been working on a DIY phased array radar, and am at the point where I'm writing the algorithms for converting signals at the array into an image. It's a very simple problem with two antenna elements... But add a third, and suddenly you need to worry about focusing. Like a total noob, I'd heard "parabola is best shape", and indeed simulations showed it is... At infinite distance... And I was struggling to understand why at close distances, a spherical formula performed better, and everything in between had off-axis blurring. Bam! Conic constants! Luckily I wont have to grind any funky lenses. A few more lines of code, and I can focus on everything at once! 😁
That sounds so fricking cool holy crap
You luckily don't have to grind funky lenses? Yeah you really don't have to, because I guess building and coding radar interpreting software is already hard enough. Do a video about it if you don't have already.
@@AllisterCaine The radar signal processing isn't too hard. Its a lot of FFTs and inverse FFTs with some filtering and reordering of data. The hard part is processing all that data and displaying it graphically in real time. You have to get very close to the hardware, and do as much processing as possible on the GPU. At this point, all the CPU does in my code is hand a batch of samples to the GPU, and it does the rest. I suppose that part would be worth a video.
Why haven’t you made a video about it??!?
Do you have a channel or page for the phased array? Love to see it! What's the application or is it just for fun?
I'm an optical scientist and I am impressed of the wonderful detail of your content--and your small tidbits of humor such as your girl in the window, ;)
That really is some incredible software!
As far as making a constant-strehl ratio variable mirror, I suspect that would actually be relatively easy using software like fusion360’s strength calculations. Or the same thing with some programming. By modelling the glass as having some tensile and compressional constants, you could do some numerical equation solving to find the optimal thickness gradient for keeping that ratio constant. While not simple, it’s certainly better than trial and error.
I saw an article many years ago where an amateur astronomer took a spherical mirror and glued a screw at the back using epoxy. He made a cutout ring also at the back of the mirror like in your set up and using the screw, he was able to correct the mirror to a parabolic shape.
Interesting video :)
This channel is a godsend for people who have a constant itch for science, and are tired of the oversimplifications of general scicomer’s.
3:15 love your sense of humor. Lol
by the way I wish people who made Hubble telescope, watched this video first. 😜🤓
One of those rare videos on youtube that are extremely interesting on a unique and intellectual level.
0:46 so the magpie is at least 50 nm flat?
Another excellent presentation with a great deal of information clearly presented, and a pleasure to watch. Laughed at the humor on 'looking at something close up'
Love the conic constant explanation with visuals I have seen similar but the fact it was thrown in to remind me of it. And now typing the further explanations of each are amazing
I literally went to another world while listening to him..
Your skills are of incalculable value for a post apocalyptic scenario. We could get back to normal a lot faster. Optics are so important for our modern world.
At first I thought, _Wait! Go back to your neighbor showering_ ...
But you added some great info re conic section-use for focusing parallel vs localized rays...
Eg., to focus rays from a nearby point (local) with an elliptical segment is awesome. Thanks!!
Thank you for such a great video! Your experiment is motivative. I have polished couple of mirrors using bath interferometer and dftfringe.
Thanks for your theoretics explanation. People more use this method to make Schmidt correctors.
Loved the visual explanation of the conic constant
Perhaps ... the Finite Element Analysis software could help optimize the shape/thickness profile of the mirror lens... and possibly open avenues for some additional tricks.
Excellent presentation ... as usual!
0:35 That's the age where birds normally get kicked out of the nest. The parents usually stay nearby and chase away predators (or at least try to) until the fledgling learns to fly.
Fantastic presentation of a complex subject, fascinating to watch, very informative
These videos are very interesting, you are a realy good communicator. Thanks for sharing with us!
I learned a lot. But then I can't build lenses because I lack the necessary materials. I envy those who can. This is an in-depth explanation of how to perfect a skill which is quite remarkable.
Mr. Jeroen gives a very high quality content to the public. I really appreciate it!
Very interesting and such a good explanation of the different kinds of curves!
Always enjoy these videos.
Stopped and liked the video, right when I saw the for lady in the window. Your sense of humor is great!
Please keep making such videos, so much good theory and knowledge for just a fellow Maker.
sorry to hear what happened, Jeroen. Thx for sharing!
I like the sheer honesty of this man...a very refreshing quality in this day and age.y respect to you sir
Excellent explanations and graphics. You should write a book about it.
Exceptional video. Just as you mention at the end, a failure as a useable device, but a success as a learning initiative, I can say that I learned here. I am not an amateur telescope user and I haven't used optics in any of my work except for a few microscopes, but the optics part was not something I had to look into. I am interested in many things and sometimes think on optics. I am pursuing invention and so I like to learn about many different things and I find that the more broad my scope there ideas flood to me. Just in the past couple of days you have initiated a few floods for me!
3:18
Ahahahaha :D
Excellent! Congratulations!
thank you for getting me interested in optics
Could you fill the void with some sort of epoxy or resin that can be dissolved later on to fix the issue of the lens flexing?
I don't understand how such a filling would solve the problem.
Beautiful, beautiful work.
Very information dense and really interesting/cool. Thanks and keep it up.
That magpie won you a sub
Awesome work!
I loved finding out at the end that the goal was actually not reached. It would be very interesting to see a different geometry, where changing the internal pressure would cause the back and front parts to move linearly with respect to each other instead of bending. Zero bending. Perhaps this could be achieved by use of a rubber-like circular band placed between the back and front lenses. The band would be in the shape of a perfect torus. Would this work? No, it would only change the focal length, not the conic constant. I can't help thinking that there must be a solution, a way to change focal length in such a way as to avoid any aberration. Maybe that's why expensive cameras use several pieces of glass attached together to focus light.
Fantastic video. Thank you.
Impressive and very informative. Goed bezig!
Its obvious that you are having fun! Are you familiar with the work of Gerard Lemaitre and his numerous colleagues at Marseilles LAM observatory? Look for example at the "Rumsey Telescope" where "bend and polish" combined with substrate design allows one vaccum to produce two separate coniciods that meet in slope AND position at an intermediate radial zone of hte substrate (so a continuous optical surface, with two differnt conicoids). This is used to produce a three-mirror anastigmat with Primary and Tertiary on the same substrate, and is made with an evolute of the technique you discuss. Norman Rumsey invented this type of TMA in 1969.
Brilliant.. thank you.. I now know what spherical aberration is and also confirmed my suspicion that engineering is always an approximation inside a tolerance determined by the cost of achieving it. It reminds me of a principle in thermodynamics that to decrease the entropy (increase order) of a system of particles you have to increase the entropy (increase the disorder) of the surroundings by more. Which is why abiogenesis is impossible.
I like the dig at the end, I thought I knew what you meant but I had to look it up to be sure. The fact that crazy things can happen because of randomness does not mean that abiogenesis is possible.
I don't know if this is common among other viewers of yours but I'd love to see a video dedicated to interferometry. People make all kinds of crazy measurement tools that measure depth, angle, etc of a surface and as someone who one day wishes to get into precision machining and even perhaps semiconductor manufacturing I'd love to get some insight into how some of these tools work.
Regardless, amazing video. I understood everything up to and including the interferometry part, but got a bit confused with the whole rest of the graph stuff though I think it's all just to rate the accuracy of the parabola and how it'll vary as a function of the pressure. Thank you for yet another mind boggling video!
Filling the cavity with a liquid, and sealing it, may help when polishing.
How would that help, exactly?
why not apply a positive pressure in the last grinding process ?
Would it help to do more polishing, *while applying hydraulic pressure* of some value(s) ?
This is splendid. Thanks! (I hope the magpie is doing well.)
Thank you very much for this content.
your channel is a treasure
this is fascinating!! been dreaming about such a structure for years, but i have a few questions: 1. why do you need to grind the surface of top plate when it is already glued into one whole system? can you grind it before assembly? 2. why do you even need to grind it into a curve? i though with low enough pressure, a flat surface would get curved into spherical shape automatically. 3. under pressure, how stable is such a system?
I like the bit on conics especially. So a sphere focuses light from its center, an elipse focuses light from a point a finite distance away, a parabola focuses light from infinity. So does a hyperbola focus light from beyond infinity?
Personally I would formulate it a bit differently: the hyperbola can correctly focus a convergent beam (generally containing a spherical aberration). This in contrast to elliptical shape, where the beam coming from the object is divergent.
@@HuygensOptics Hey thanks for the reply. So much great info in your videos. Cheers.
i have no clue about anything ur talking about...
but ur videos are incedibly charming!
Very informative vedio thanks for sharing.
I don't understand nothing, but I love to watch these videos
Thank you for sharing. This may have been a failure for you, but it was a huge learning experience for me!
Love this video! Very cool experiment indeed.
Question: what would happen if you used a reflective film for the front element rather than a glass element? Wouldn't it resemble a parabola more closely under vacuum?
Also, I didn't see if you had a liquid in the syringe or was it just air, wondering if it would be easier with a incompressible liquid.
Another great informative video. Thank you.
I'm still curious what's the use you had in mind for the small variable mirror.
I did not show this in the video but I made a convex version of this mirror simultaneously with the concave one. Idea was to use the convex version to test the principle in a "classic cassegrain" configuration, where the secondary is a hyperbolic convex mirror. But for the convex version to work, I had to apply too much (positive) pressure inside the cavity. Forces on the glue quickly became frightlingly high and since it was tensile stress, this would not work. So instead I just used the concave mirror to test some of the properties, which was way easier for me than testing the properties of the convex version. In short: the concave mirror was sort of a by-product.
@@HuygensOptics Could the convex lens be glued inside a lipped tube so the glue is in compression? Using water for pressure instead of air would mean no energy is stored in the compressed gas, so a sudden failure would be less energetic. I think the classic cassegrain is a great idea.
I'm wondering if you are aware of the Sky and Telescope Nov 2000 article "Flexing Spheres into High Quality Telescope Mirrors" where they do flex a mirror without a vacuum. It would be interesting to measure that in your test apparatus and perhaps it could be the subject of another video!
I second that. I have built flex mirror scopes. Superb. I have not worked out if vacuum would do the same job. I know they use vacuum as demonstrated to make Schmidt telescope corrector plates, so...probably...
Very interesting and superbly presented as usual. Please tell me you still get visits from your adopted bird?
I got a large Germanium lens which uses a giant front element. It's concave on the inside and due to the nature of Germanium and the coatings, it's quite reflective in the visible light spectrum. I don't know if it's parabolic or spherical. But I believe it's spherical since it looks machined. Now I got a few test I can try to measure it.
amazing topic
Just wondering if localized heating and cooling of the glass has been tried to raise parts of the glass that need to be ground off and lower good areas for protection? Seems like it might concentrate force on high spots for faster and maybe even more accurate grinding/polishing, maybe also to vary shape in use instead of using pressure. (Not sure how it would be done but picturing a dense grid of individually controlled peltiers mounted to the back surface of the mirror as it is being made. (or maybe piezo elements to apply pressure instead of heat)) Also, is there any such thing as an inexpensive source of glass for making large (300mm+) telescope mirrors?
Simplest way is not to deform the mirror, but to use deterministic polishing: just polish in places where you need to remove material, by using a smaller tool and varying the contact / polishing time over the surface of the optic. For example as illustrated in this video. th-cam.com/video/tMp0sI3aYEU/w-d-xo.html
Seriously good on ya man , your little corvus buddy there is indeed one of the most intelligent animals around, especially when you consider what they are capable of with such a small brain, they really are an evolution marvel
Wonderful content. Is it possible to use a more plastic material since the coating will be a mirror ?
Seems possible, but how would it solve the variable conic constant problem?
Always wanted to know how these were made! Didn't know pressure could effect them like that!
Nice video. I have a query, 3:00 What happens to the parallel rays non parallel to the principal axis?
Good question. Parabolic mirrors only give a perfect image on the optical axis. For off-axis rays they suffer from an optical aberration called "coma". See en.m.wikipedia.org/wiki/Coma_(optics) for more information.
@@HuygensOptics ohh thank you so much. I have been googling for many months parabolic reflection of rays non parallel to principal axis and just couldnt find the buried answer. I even tried learning simulation for reflection. This scientific grammer/definition is sometimes very dificult to get. Thank u
The ELT will use adaptive optics that are actuated by very small mechanical "push-pullers". Any thoughts on a comparison between using compressed air vs mechanical actuators? I guess complexity and scale are some of the pretty obvious tradeoffs.
Very interesting !
Thank you - good job - i've been reading about "how to make a lens" HowTo back in 1996 a method with thousends repetitions of particular movements but never got into creating one - i see you do that repetitive method of directed scratching
thats so sick thats so cool holy crap
Just subscribed ! Your content is amazing :o
I was in instrumentation and it's really cool to see practical designs so well explained, I really miss this domain.
Relative to the Strehl problem, since we are talking about microns here, do you think you could just engrave concentric circles with a higher density of circles with bigger diameters ? (the term is "graver" in french, i am not sure how it translate )
Have a good day !
Do you mean a fresnel lens? If so, he’s made videos about them before.
Passionant !
Rather than a conic, would a better fit be a catenoid?
Maybe a non compressible fluid rather than air in the cavity.
The oblate elipse looks like the object to be looked at is BEHIND the focus or observation point. Perhaps for extreme maginification. I designed a water lens when I was in my early twenties, later determined that I could do the same with a very large mirror and sheet of glass for long distance focusing and burning. I never made that one but always wanted to. It would be good if we could modify a mirror for laser focusing at extreme long distances, like from here to the moon, so that the lens countered the divergense of the beam through a feedback observation. Multiple lasers of different colors with this mirror tech could focus multiple beams at two miles or further to combat an oncoming threat in space. A phased array of lasers, better known as a phaser.
Amaizing
thank you
Hi,
great Video by the way.
Would a flat peace of glas produce a parabola?
I was wondering if it could be done with a protectionglas for smartwatches stright out of the box.
Hi Christian, I don't know, are they nicely spherical? You can generate a parabola (or other aspherical shapes) by pressurizing the chamber during polishing, because you will remove more material in the center with positive pressure and less with vacuum.
@@HuygensOptics The tempered glass iPad screen protectors are totally flat. I think Christian means to generate the parabola from that flat surface using only pressure, and no grinding, similar to the following video, but with glass instead of plastic. th-cam.com/video/8CLRTa_ocmo/w-d-xo.html
*8:45** You can use this shape for "stereo telescopy"?*
(but for stars the distance is so small that the stereo effect becomes unnoticeable, but maybe useful for a bird telescope or something?)
Just use 2 detectors & place 1 in each focal point? (P1 & P2)
yeah, I guess it might be usefull if you want to also very sharply observe objects at closer distance like birds or insects.
Is there a reason to make the back piece out of glass, rather than just milling it out of metal (for example)? Great video.
It's done to match the thermal expansion to avoid bending by temperature changes.
What a gem you are :D
I'd love to see you break down how the Arecibo's spherical mirror works.
Are you talking about the former radio telescope at Arecibo?
Other than the last bit addressing the mirrors failure vs a theoretical perfect one, I had a thought about the issue of the mirror bending during grinding. Could you fill the void with water and plug it while grinding? I imagine the hydraulic incompressibility would help support the center of the span, but then again I dont grind lenses/mirrros/anything optical (yet ;) ). Im sure there is something Im overlooking, possibly the bond strength of the two surfaces, though I cant imagine that being much weaker than a span of thin glass. But that was my fabrication brain's immediate thought when the bending of the surface while refining the shape was mentioned......
Sorry, completely out of my league but would masking off sections of the mirror be an optimization strategy? Like taping or painting black the outer support section and maybe some additional area so you are only reflecting light from a more uniform area.
Can you vary the pressure, to get a differential grind? ie. High pressure to remove the central peak?
But it would work only for a particular focal length. No obvious way to get a continuously-changing focal length free of aberration because of changing conic constant. It would be so nice if there were a simple solution.
I have zero interest in telescopes and I just spent 20+ minutes learning how to make a vacuum controlled mirror with a variable conic constant.
I wonder if you can remove the bump by filling the cavity with something (like wax or a soluble plastic) in the final polishing of the front element?
Hi Andrei, unfortunately that would not work, it would actually create the opposite effect. Wax and plastics have a strong volume shrink (several %) when they solidify. This would actually retract the surface over many microns. After polishing and removal of the wax (which would release the surface), this would cause a very large bump. I used deterministic polishing on the center (shown at 17:55) which resulted in a fairly good sphere. However, the problem of the non-constant Strehl was still the main issue after this.
@@HuygensOptics how about adding water/liquid & temporarily sealing the void before the final polish stage? A tube & clamp may do.
@@HuygensOptics That's a shame, but I guess the devil is always in the detail. Really interesting projects nonetheless, I'm excited to see more on the metasurfaces
@@andreithe3893 Then I'm pretty sure the next video will be to your taste :-)
Have you ever thought about making a Schmidt corrector plate?
I thought the video was about how to make a mirror but great to learn the relationship of ellipses and parabolas to a cone!
Hi, can you tell me which glue did you use?
Can you tell how did you measure the Strehl ratio?
Where did you source your GRIN lens for the interferometer?
On ebay, I think it was this one: www.ebay.com/itm/Newport-LGI830-6-Gradient-Index-Micro-Lens-GRIN-Lens-320-2000nm-UV-to-IR/114292892707?hash=item1a9c632423:g:1FEAAOSwvmxbWvp9
I wonder if you could improve the "bump" in the centre by figuring and polishing the front surface before deblocking rather than afterwards?
Absolutely - thicker glass will polish without flexing so much under pressure. You could polish the two ground radii against each other to a test plate fit, contact them together, mill the top plano surface to convex, polish that while still contacted, then decontact and run the sandblasting process. Sucks to sandblast a nice polished surface like that but needs must. You now have a nice K=0 surface to deform from, that was fully supported during polishing. There are plenty of optical cements which work just fine on polished surfaces. The same vacuum pressure should then get you to a much more negative K value
I too came for the optics but was fascinated by the magpie. Could you do an video on friending a magpie? I have been interested in friending a crow but haven't bothered to figure out how. (back to the video)
Well, there is actually a ton of video's on TH-cam about friending magpies and crows already. There are many ways, but if you want the bird to be really tame and to trust you, the only way is raise one yourself, so you should have a bird that is very young (too young to fly basically), like the one that I had. It had fallen out of a nest prematurely and the parents were so busy with the other 2 young that they did not bother to feed him any more. You should put in a lot of time. Another way to befriend magpies is shown in this video, however the birds will never be a real companion: th-cam.com/video/EXYf2DTOsvI/w-d-xo.html . Btw, the magpie I had was attacked by a cat and it being severely damaged, I had no choice but to bring it to a bird hospital / shelter . However it has recovered after several weeks and has been returned to the wild. As was actually also my intention.