Making a monolithic telescope Part 3: Figuring & Testing
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- เผยแพร่เมื่อ 17 พ.ค. 2024
- Use the following links if you want to skip to the next chapter of the video:
00:00 General intro
01:54 Required level of precision
07:12 Measuring surface shapes with interferometry
10:46 Fringe evaluation with DFTfringe
12:12 Optical Pitch polishing
17:19 Making molds using 3D printing
18:18 Results with variable surface tools
21:06 Primary mirror
22:20 Point Diffraction Interferometry (PDI)
26:48 Visual performance
29:58 NO MORE NAPS (featuring Dr. Fullersheit)
Links mentioned in the video:
Website with the best and most detailed information on telescope optics:
www.telescope-optics.net/. This is the direct link to the page about the different criteria and how they relate to aberrations: www.telescope-optics.net/effe...
The 3D-printer used was manufactured by 3Bfab. More information on their products can be found on their website: 3bfab.com/ (not sponsored content - they did neither ask nor pay me to show their product)
DFTfringe software is programmed by Dale Eason. This is the link to his TH-cam channel: / @daleeason9687
The software can be downloaded from:
github.com/githubdoe/DFTFring...
This is the link to the interferometry group on DFTfringe that Dale runs:
groups.io/g/Interferometry
The Point Diffraction Interferometer can be purchased for about 50 Euros from Michael Koch at www.astro-electronic.de/
(not sponsored content)
Other videos in this series:
Part 0: Tiny telescope concept video (featuring Rik): • Why is this Space Tele...
Part 1: Optical Design and Aspherics; • Making a Monolithic Te...
Part 2: Machining Glass; • Making a Monolithic Te...
Special thanks to Dr. Liam Fullersheit for his guest appearance. (;-). - วิทยาศาสตร์และเทคโนโลยี
It's really great to see everything coming together in the final product. Very cool project! Did you ever find out about the difference in apparent focal length vs designed focal length? Is it possible that the microns of surface adjustment can affect the focal length that much?
Thanks Ben! The focal distance is actually very sensitive to small changes in the curvature of the two reflectors, an effect which is amplified even more by the concave exit lens surface. The change in focal length is due to the fact that I started with the secondary, which did not have the exact radius of curvature after correction. Because I steered on the total output of the telescope, the specs of the primary were even further away from the target specification. So yes, a few microns can make a huge difference in the Cassegrain configuration for focal length. For this project it was actually no problem because it was all about learning as much as possible and making mistakes.
@@HuygensOptics Well, assuming you learned a lot more making this telescope and these videos, than I did in watching the latter, I'm guessing you learned quite a lot! Very cool! Kudos on some great work. And yes, very interesting; thanks for sharing!
𝑓𝑎𝑤𝑛𝑠
I could watch ol' Huygens and Ben make mistakes all day. 😍
... I could watch from far away, safely, if i had an ultra compact Cassegrain telescope, though.
@@owlredshift haha, indeed.
@@owlredshift Ooooh.....so did you order one too?
though these videos i'm just drawn to think how much better/faster i would have learned at university if taught through projects like this one. Having to tackle both theoretical and practical/technological problems and solutions in order to achieve a practical goal.
This x1000... I got bored at school and did terribly. Dropped out of math/chemistry at grade 10 because it all just felt so abstract with no real use. Now I really enjoy watching 'edutainment' videos like this! If school had been like this I'd probably still be at school and loving it lol
addendum:
I realize and appreciate that:
1) most of the solutions to practical problems in technology are overcome by a deep and rigorous knowledge of the model, physical phenomenons and mathematical instruments at one's disposal
2) in order to operate the aforementioned solution and perform critical analysis on the work done and the results obtained that knowledge is necessary.
But I feel like that's the only thing that’s taught in engineering (the course I’ve chosen and that I can have a pov on) up until one reach its master thesis or doctorate.
I like the field ‘because it translates physical models into fruitions in a useful manner, and having it taught in the way it is feels both -that it misses the point and really *inefficient*.
Also given how our memory work, and the prevalence it gives to physical experiences and problem solving over theorical knowledge on its own,
it’s really baffling how teaching it’s still at the point it is, in this century. It’s seems to be much more a result of historical heritage rather than passing down of knowledge
The thing is, my optics courses were, what, 80 hours of lectures, 80 hours of exercises, 150 hours of homework. And 20 hours of experimental lab hours. To learn classical optics then ondulatory optics.
The videos show mastery of plenty of different skills.
You need a thousand hours at least to get to such a broad knowledge.
There is a reason school is boring. This is just like "Learn programming with Python in 20 hours" bootcamps. Real programming mastery takes hundreds of hours for the basics and thousands for mastery. And it requires an IQ in the top 10-20% range to be achievable at all. And an autistic personnality to enjoy it enough to cope with the years of practice.
Yep, I really didn't enjoy university and struggled more than expected because the method there was very much to front-load a lot of information - usually via very dry lectures from soft spoken people in warn, dimly lit rooms - for weeks or months then spend maybe 10% of the time trying to apply that learning. Which absolutely does not work for me.
I ended up leaving and taking a very short (15 week but very long hours and a lot of volume) software development course instead where their stated approach was the exact opposite. Start the day with an hour or two of lectures, then spend 6-8 hours learning by basically diving in and trying to build something applying that day's learning. And I learnt more in a week there than a year at university.
That's stayed my approach for years now. If I'm about to take on a new project outside my knowledge, I'll spend a few hours researching and immediately start trying to create something. It's a bit of a "smack head into brick wall until you figure out how to break through" approach but you find all the pitfalls, you learn why something is done a certain way by seeing the relationships in action rather than being told to do it and every step, mistake, breakthrough etc. is remembered and you don't make the mistake again.
I could spend weeks explaining every minute detail in mathematic detail about how exactly to build a working combustion engine (no I couldn't), but you'd retain a fraction of it and probably run into endless unforeseen problems when you go to build one. Or, I could break the construction of one into daily chunks and explain each one while you built that part and you'd probably understand it a lot more intuitively.
@@GoughCustom Let's be honest. Even tho this is an educational video no doubt, we're all just wasting some time procrastinating here. And that's easy. Watching a fun 30 minute video without any expectations is very easy. Much easier than reading a book, knowing all the while you'll have to show your acquired knowledge in a quiz later.
No matter how you put it, it's very difficult to make school fun, for everyone, all at once, all the while being educational. Probably impossible.
We had a teacher in high school that gave us TH-cam videos to learn about some math concepts, and the videos were great don't get me wrong, but most kids either found them annoying to watch regardless or they refused to watch them at all.
Honestly, this video series is perhaps one of the most interesting I've seen the entire time I've been on TH-cam. It makes something quite obscure much more accessible.
Obscure? It's optics! 🙂
You could almost say that this brought it into focus.
I'll see myself out.
Setting aside your disappointment with wavefront accuracy, I have to say that your presentation and explanation are of the highest quality..! Many folk can grind glass, and perhaps expensive machines can do it more accurately, but very few here on the 'tube surpass your quality of content..!
Aww hell yeah! Looking forward to watching this, and thanks for continuing the series!!
@@russtuff hi Russ! No surprise that people of good taste, like ourselves, would run into each other here! 😉
Been following you since your first few videos, and I’v made AN ABSOLUTE TON of knives from the inspiration of your channel. Thank you
@@hullinstruments awesome mate! Really glad to hear!
Incredibly niche topics explored deeply, with the perfect amount of detailed conceptual explanation. Engineering poetry. Solid state engineer with only a passing interest in optics, yet these are captivating. Thank you for these incredible videos!
I have an idea how to make the contrast better. I believe a problem with black paint is that it’s not intended to be black to what it’s painted on but rather towards outside observation. This means that some paints rely on their drying process to create a surface structure that helps with absorbing light. It obviously doesn’t do that on the side that’s sticking to the material though. I believe a method that could work well is to use an epoxy resin in which you use something like activated coal as a pigment as this should absorb light very nicely.
I admit I don’t have any experience in this field but I believe this might be worth testing.
The thing is that the paint does not go into the small sub-surface cracks that resulted from the diamond drilling. The solution is quite simple: one should polish these surfaces and then cover the interfaces with a black paint that has a polymer matrix with the same refractive index. That would work just as well from the inside as from the outside.
@@HuygensOptics Thank you for your reply and clearing things up!
Actually I thought of those things too but wasn’t sure if that was a good idea or not so I wasn’t sure if I should mention it 😅
Guess I should have…
I still believe using something like suspended activated coal or some similar type of pigment could be very effective though.
Edit: I also wasn’t sure if or how the refractive index would make a difference… My gut feeling said it would be important but I somehow wasn’t sure if it would effect the light ever leaving the glass and hitting the paint or how that interaction worked…
@@HuygensOptics Would cutting baffle grooves into the outside of the telescope help too?
@@HuygensOptics or, cover the interfaces with a polymer matrix with the same refractive index in a vacuum chamber to remove bubbles, fill the cracks, and THEN paint it with the same base polymer. But idk will that work or not lol. But I guess my idea is to make a smooth surface, with polymer matrix instead of polishing it.
@@HuygensOptics I'm no expert, but I thought the old tried 'n true method to blacken ground surfaces was to just paint the outside with india ink. It's so thin that it wicks nicely in to the uneven surface, and you can do multiple coats/clean up mistakes fairly easily.
Cheers to you.
I believe the quality may improve when a long black cover cylinder is placed on the lens.
Yep, that's correct and it improves contrast quite a bit!
I would watch SEVERAL hours of you explaining all of the details. It's fascinating and your explanations are incredible.
Only 200? It deserves a way bigger success! Thanks for post!
This increased my appreciation for industrial telescopes
Absolutely superb set of videos. In a world of dumbed down reality tv and banal pop culture, you stand head and shoulders above the dross that passes for entertainment these days. Bravo.
The end result was excellent considering the accuracy required and first attempt.
Love it. My take away seems to be "use a cnc aspheric grinder to reduce masochistic rage"
This video can be used as lessons in university. Incredible details. Actually never thought how many details and craftmanship are there for making something that looks simple. Bow to you champion :)
This is the best TH-cam channel. Period
Superb! Superb! Thank you! As always, a wonderful journey into the art and science of really interesting optics. The skill and ingenuity on display is an absolute inspiration, and congratulations on even realizing Rick’s challenging but inspired design. As always too I cannot thank you enough for the clear and concise education in your videos, it is second to none. So congratulations and thank you!
Sir Patrick Moore's monocle🧐 approves of this splendid video series.🙂
How is it, that all the great masters of their crafts in terms of machining have the same amazing sense of humor?
I'm really enjoying this series. It has some close parallels to mmwave dielectric lensing. It's really useful to see how the issues are handled at 600 THz rather than 122 GHz.
This is the secret part of TH-cam where highest level of specific knowledge is hidden. Glad we found it
21:01 that gargantuan wave-front error is a nice touch
Whow, making this thing takes space-grade level of patience!
Love the videos Mr huygens,i would have learnt so much from you, had you been my university lecturer,there is so much detail here,you include problems,and are open about mistakes made,This is what education should be like IMO,step by step explanations,with details of problems,as well as progress made,theoretical and practical,beautiful stuff.
Your sense of humour is terrific. i thought you northern europeans were born without the humour gene!!
Anyway,im a firm subscriber. BTW i originally trained as a radio and tv technician when i left school,yonks ago.Your explanation of the analog TV transmission system is spot on..
@ Julian Richards: the British have been known to be humorous, on occasion ...
I have never really given any thought to optics, but after watching this series I am utterly captivated. And I doubly appreciate the fact that, as a layperson, you take the time to explain what you're doing and why. I'm astonished at how accessible you made an otherwise very complicated topic.
wow, wat een geweldig project. Petje af! Dat Pitch Polishing leer ik graag nog eens wat meer over. Lijkt me leuk om eens van dichtbij te zien
Did i just watch three videos with extremly technical concepts, extremely accurate techniques of all kinds, years worth of experience in order to even begin with, about 200k worth on ultra specialized machinnery, months of planning, hard work, tweeking everything to finally compare the product to a cheap 200usd 300mm lens and find out our thingy sucks? lol
Now for real, i enjoyed every second and loved the whole project.
Congrats!
Thank you! This was the single clearest and best exposition of a technical topic ANYwhere on TH-cam!! You are a master, not only of glass but of narrative. Bravo!
I would consider this to be an excellent result even if it was a 2nd or 3rd attempt, let alone the 1st one. Great job!
28:53 The black spray paint makes the frosted inner surface behave like a reflective diffuser.
I think a less viscous paint would more thoroughly seep into the tiny pits before drying. Spray paint particles might even be too big to properly fill them in (possibly creating a refractive/reflective nightmare of tiny air gaps). A more matte/flat black wouldn't hurt, either.
black 3.0! or some of those super dark absorbent paints, they're thin and goopy enough to mash into the holes in the glass making perfect contact
@@l3d-3dmaker58 You're thinking about the wrong side of the butter on the bread.
We know what those ultra-black paints look like on the exposed surface, but that doesn't mean they'll be equally non-reflective when viewed from the adhered side.
Also, Black 3.0 is an acrylic paint. For an application like this, the particle sizes of the paint matters. Acrylic and latex paints have relatively large particles compared to others pigments like India ink (an order of magnitude difference in particle sizes).
I'm not saying it definitely won't work, just that it would require some experimentation. It might not be the obvious solution for blacking out an interior surface that everyone seems to be suggesting it is.
@@davidg5898 I wonder about surface treating the glass before painting. imagine sand blasting to get a very rough surface then painting that. The "spikes" sticking into the glass might help to reduce low angle reflection, high angle reflection might gets corner reflector type double bounce you might be able to use to get two chances at absorption.
Going down that line somewhat, you don't actually need to absorb the light at the interface, you really just want to stop it from bouncing off and back into the scope. If you put a material with a different refractive index on the outside perhaps you could create a reversed optical fibre where light finds it easy to leave the body of the scope but is bent back out when it tries to return.
perhaps rather than paint
@@zyeborm If anything, I think a smoother exterior surface would be better.
1/ It eliminates/reduces the problem of making sure any blacking pigment gets as deep as possible into microscopic crevices. The deeper you make any pits in the glass, the more you have to concern yourself with microscopic properties of pigments and how to apply them (and then you start over-engineering with ideas like curing the pigment in a vacuum chamber).
With a smooth surface, if you can find a blacking pigment (or mix a black polymer) that's a close match to the glass' refractive index then the reflections will be hugely diminished.
2/ The taller the pits are at the sides of the telescope, the more likely their tips will become a significant source of refraction.
Along the lines of your thought process, I was initially going to suggest cutting 2 or 3 rings around the perimeter and blacking them out, comparable to the light baffles in a normal telescope, but then realized it would become more of a refractive problem inside an all-glass optical train than it is in a normal telescope's air tube (again, due to which side of the baffle's surface you're blacking out).
3/ Specular reflections from a smooth surface won't harm resolution as much as diffuse reflections from a rough surface. Most specular reflection rays won't be bounced into the light path that goes to the exit pupil as opposed to the random paths that diffuse reflections take.
4/ Specular reflections are easier to deal with than diffuse. A simple light hood extending past the front of the telescope would significantly cut down the amount of rays that would otherwise end up in the intended light path.
Those 3D printed pitch tools are absolutely brilliant. I've often wondered how to grind aspheres without a lot of fixturing and tooling. Bravo
Some weeks ago I had a problem with one of my vintage Leica lenses, the black paint on the inner lens elements was chipping off effectively causing low contrast because of stray light. After some research I found that Indian ink works surprisingly well for coating optical elements and reducing stray light reflections, thus improving contrast. Hope that info is useful! Excellent video as always!
This has been a fantastic series! Though I doubt many of us would attempt such a complicated grind, the background knowledge, testing instrumentation, design compromises, concepts and techniques really hit home. It's such an elegant project to "bring it all together". Love it!
I love that your projection lens is a Canon 55mm f1.2! Wow.
The skill and experience going into this is only rivaled by the talented presentation. Complex physics are made understandable in a very rare way. As a person with only very basic understanding of optics I'm riveted to these videos. Thanks!
The polish of your presentation sharpened my fuzzy understanding of optics in several areas, wavefront especially. Considering the level of precision and the tangle of dependencies I'm awed you got the telescope working so well. And by hand! Your explanations of how you accomplish that make sense to me but it still blows my mind that you can work at nm scale with your hands.
Very cool.
The amount of information is great.
Thank you for your videos.
Much appreciated.
Haha, "bad wavefront".... this video and the results are absolutely amazing !
This has been one of the most fascinating video series on this website! Thank you for putting it together.
I cannot describe how excited I am now, just respect!
Incredible work, great video, and the performance from such a small monolithic lens has really impressed me!
Astounding; an incredibly practical explanation of Cassegrain, which I had never been able to understand. These 3 videos are some of the most instructive that I've ever seen.
Wow, so fascinating! It was so interesting to me to learn of all the second-order effects that came into play, and the idea of using 3D molds to form the pitch laps was brilliant!
"Important optical experiments always prevail over a bit of privacy." Amen!
That outro segment was fantastic. I also think that it's great how much effort you put into the explanations and documenting of this project.
Incredible project. Also, you have done an excellent job of describing what you are doing to someone who has zero experience with optical engineering.
awesome to see this series again. Incredible work on this project!
There is some artistic value to the imperfection of the telescope's captured images, I kinda like the soft focus and color effect achieved with it.
Thank you for the series, looking Rik on the corner of his studio just chilling when polish his lenses seems so simple, then you show all the math and equipment necessary to get it done, there's no price in this knowledge you shared with us.
Super impressed by your thorough treatment in both theory & practice.
Amazing stuff Zen Master HO!! Some years back, it would take me about 12 hours work to prepare a 1 hour Mechanics Lecture at University. I could not even begin to estimate how much time and effort went to producing this 30 minute masterpiece. I would hazard a guess at weeks....if not months?
Thank you!! Oh - and as fascinating as the field of Optical Physics evidently is - I for one would fear the real possibility of insanity were I to attempt a project requiring this level of precision, patience and mathematical/scientific know-how. IMPRESSIVE STUFF INDEED.
Now get Cracking on that order for 'Sales' 😂😂
Thanks for the compliments. With this video series out of the way, I can now start mass manufacture...😅
@@HuygensOptics where to buy??
I like how I was wondering about this yesterday and here it is uploaded yesterday.
Thank you making this series. I’ve learned so much!
Impressive, very, very impressive..
And I appreciate the effort to keep the construction methods down to something that can be done with fairly simple 'maker' tools. Makes the project surprisingly accessible.
this channel is crazy good. i'm really glad that you're willing to dedicate time and effort to making videos on technically advanced subjects that simply can't get mainstream level popular.
i particularly enjoyed the part where you physically translated the desired shape of your lens onto your pitch surface pattern, it's genius. i thought how I'd do it many times and I could have never come up with this.
As always, top notch presentation, and probably the only channel with this kind of deep dive videos.
Fascinating process! I found the use of 3D prints in the polishing process especially interesting.
this is amazing! perfect balance between well explained and well summarized
we need more quality content like yours on TH-cam, thanks for your work
The technical level of your channel is astonishing. Thanks for this.
Fascinating to see. Thanks for the series.
From a layman's point of view its awesome, what a great series...cheers.
This was a fascinating experiment! Thank you for sharing it.
This has been a truly outstanding series - wonderful
Thank you
Awesome! Thank you for sharing all that experience!
This is isanely interesting!
Being an amateur telescope builder myself, I can proudly declare - your content is TOP !
Can't believe I'm living in a time where this kind of exelent educational content is available at a moments notice, for FREE! Amazing video, you got me excited about optics again for sure. Would you consider making another one in the future and improve on the things you learned from the first?
HOLY SCHMOLY!!!!!! I am BLOWN AWAY at how powerful that little beast is!!! I'm willing to bet that if you had access that that CDC machine at Edmund Optics and you got that design perfected, you could sell these things like HOT CAKES!!!! - But I get the feeling that's not something you're looking to do..... ANYWAY....
I didn't think something so small was possible! I mean I know NOTHING about telescopes, but I saw this video randomly (well the part 1) and decided to stick around to see how it turned out and I LEARNED SO MUCH!!!!
THANK YOU!
I'm just amazed how interesting and complicated optics can be! Thanks for sharing this work!)
For a hobby astronomer and layman-interest in optics, this is an insane amount of knowledge and experience condensed into 30min. I hope this is documented somewhere for future generations. The results are amazing, almost magical.
Your videos are excellent! Thank you very much for taking the time to present your work in an informative and entertaining manner. I look forward to your future work!
Thank you for all the hard work in making and sharing this series. I learned a lot, great content as ever.
Really awesome series of videos. thanks for them. I enjoyed all of them a lot.
25:09 your frustration reminded me of this memory:
In the 1980’s I read an article in a Reader’s Digest issue about the mirror for the Hubble Space Telescope’s mirror’s manufacture. The article was the difficulty experienced by the team contracted to grind the mirror. It as to be ground by a computer controlled apparatus of some sort. According to the article (and as I recall it, which may not be very accurate after all these years) the team of engineers and techs, try as they might, could not get the mirror within contracted specifications. It would be ok in one spot but out in another, and correcting the errors over there introduced error in another place.
At the time of resting I recall being rather fascinated. Of course, being in my early 20s and from a small rural area adjacent to an only slightly less small town in Washington state, U.S.A., and having only just barely graduated HS I really didn’t understand any of the technical details. But in the frustration experienced by the grinding team the lead guy, who was considered a sort of magician with lens grinding took the mirror home to grind it by hand.
I am not certain, now, how that could have been possible. And perhaps my recollection ti on if that is incorrect. The mirror was almost 8’ (2.5 m) in diameter and just looking at the picture of it being shaped at Perkins-Elmer (upload.wikimedia.org/wikipedia/commons/9/91/Hubble_mirror_polishing.jpg) it’s hard to imagine that thing being transported anywhere. But they were under great pressure to finish and finish they did. The guy who supposed took it home even won some award for his outstanding work and sacrifice to the cause. As I recall the effort drive him to retirement.
Of course we learned later the mirror was defective and had to be corrected in space.
I wonder if the relative smallness of your optic wasn’t just as hard as they experience with the Hubble.
by far one of the coolest channels on TH-cam. please please continue to expand the scope of technical consciousness !
I would love to see a new version of this, with improved methods.
Thanks for documenting this fascinating project in such a clear and information-dense way! As a layman in optics, I feel like I have just received a gift of powerful new analytical tools. I hope I get a chance to apply them sometime! Thanks again! Looking forward to the next video!
Thank you so much! Having ground, polished, tested, (repeat, repeat, repeat, etc…) a 200mm diameter ~f6 parabolic mirror, your work is exemplary! I enjoyed the videos on many levels… 😀
as a sound guy i gotta love the coarse simplifications that lead to quarter wave rules
nice detailed video on manufacturing and tools and calculations you have used .
Bravo! You videos are absolutely brilliant, you give me so much insight into optics, quantum mechanics, I have learned here much more than in other educational content on youtube. Great balance between theory without "dumbing it down" and showing things practically. This video felt like 10 minutes long to me, I didn't intend to watch all of it and then it was over. Looking forward to more videos of yours!
Echt een heel mooi project! En geweldig goed gedocumenteerd, zeer prettig om te kijken!
Finally, a seeing brick
Your videos are endlessly fascinating, educational, and entertaining to me! Congrats on this monolithic....errr... monumental project!
What an amazing project. Wish you all the success.
Absolutely fascinating project! Congratulations! It works!
Your dedication is admirable. I look forward to your next project.
Great series of videos. Thank you for sharing such wealth of information.
I love these videos, it amazes me that you have managed what you have with hand polishing. It's really interesting that you've managed to pack a 400mm focal length telescope into such a small and incredibly robust package.
Been waiting! And even more mind-blowing than i expected.🤯
Very interesting!!!! Never was interested in optics before, but your videos have changed this totally, thank you for that!
Eagerly waited for this part, thanks for sharing.
Love these technical deep dives.
This was an extremely informative lecture, thank you!
Incredible! Thank you for sharing!! I would never get to see such a cool industry on my own. Thank you so much!
Incredibly informative, with a touch of humour. Brilliant :)
Thank you so much! 😊
Another fantastic video.. Thank you for sharing your incredible knowledge with the world. Absolutely fascinating! 🙂
It's very interesting material science. I use a lot of time mirror-reflect lens for long focal photography, and this material is very interesting for me.
25:00 superhuman interpreting wavefronts in his head, love it - if you can imagine the 3d space, and imagine the waves, somehow you could get used to this, but damn! very cool
please continue the series in depth. very interesting
Very cool! Really enjoyed the 3 part series, I coulda gone for even more!
outstanding work with all that effords you put into
Amazing - really interested in how the focal length was so different - well done all the same