Huygens Optics - 2022-06-10
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: https://www.telescope-optics.net/. This is the direct link to the page about the different criteria and how they relate to aberrations: https://www.telescope-optics.net/effects1.htm The 3D-printer used was manufactured by 3Bfab. More information on their products can be found on their website: https://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 YouTube channel: https://www.youtube.com/channel/UCPj57WFSSLpVqPir7Im-kiw The software can be downloaded from: https://github.com/githubdoe/DFTFringe/releases This is the link to the interferometry group on DFTfringe that Dale runs: https://groups.io/g/Interferometry The Point Diffraction Interferometer can be purchased for about 50 Euros from Michael Koch at http://www.astro-electronic.de/ (not sponsored content) Other videos in this series: Part 0: Tiny telescope concept video (featuring Rik): https://youtu.be/HxwhCmO90UQ Part 1: Optical Design and Aspherics; https://youtu.be/awOvnubFE8M Part 2: Machining Glass; https://youtu.be/A0bysBIj0FA Special thanks to Dr. Liam Fullersheit for his guest appearance. (;-).
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.
@Gough Custom 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 YouTube 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 YouTube. It makes something quite obscure much more accessible.
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.
@Huygens Optics 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…
@Huygens Optics Would cutting baffle grooves into the outside of the telescope help too?
@Huygens Optics 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.
@Huygens Optics 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.
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!
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..!
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 - 3D maker 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.
@Dávid G 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.
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!
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.
I would watch SEVERAL hours of you explaining all of the details. It's fascinating and your explanations are incredible.
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!
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!
Echt een heel mooi project! En geweldig goed gedocumenteerd, zeer prettig om te kijken!
Aww hell yeah! Looking forward to watching this, and thanks for continuing the series!!
Fancy meeting you here :)
@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
@HULL GUITARS USA awesome mate! Really glad to hear!
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.
Brilliantly done!
The technique of 3d-printing a negative mould for the polisher is a great idea!
The colour correction of the telescope seems to be quite good, too.
Then, there is also the issue that Cassegrains are always bad for day time use due to stray light directly reaching the image plane. Adding a dew shield with a single baffle in front of the entrance surface may already improve this.
Please do not let this discourage you from testing the night time performance: Jupiter, Saturn and Mars are up in the early mornings ;-)
You could also do a star test with a real star. Albireo, ß cygni, is a nice target, high in the summer sky.
In the end, it might just be that the whole system has become over- or undercorrected.
Since the first surface is flat and uncoated, you could still do some deformation there without stripping the mirrors.
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...😅
@Huygens Optics where to buy??
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 :)
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!
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!
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 ...
Love it. My take away seems to be "use a cnc aspheric grinder to reduce masochistic rage"
I find this really great even though I don't grasp the advanced concepts. Thank you for taking the time to create these - they are better than watching machining videos.. Hopefully that did not come across the wrong way. Have a great summer dude and thanks again for sharing! oh, if there are any spares left over when you're done I'd love to have one :)
That's what universities are for. Get yourself a science degree, especially physics, you'll understand all of it
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.
we need more quality content like yours on YouTube, thanks for your work
Excellent work! I know that you may not have accomplished the 1/4 lambda that you set out to achieve, but it's still an amazing piece of precision engineering.
This has been one of the most fascinating video series on this website! Thank you for putting it together.
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!
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
Those 3D printed pitch tools are absolutely brilliant. I've often wondered how to grind aspheres without a lot of fixturing and tooling. Bravo
I'm just amazed how interesting and complicated optics can be! Thanks for sharing this work!)
Wow it's so interesting to watch the whole process that goes through these lenses. It also makes me super sad because I had hoped that someday I would take the Time to make myself some photographic lenses. Seeing the relatively poor image quality you achieved after so many hours makes me reconsider the whole project I had...
I nos wonder how the man who brought you into this didn't lose his mind in the process of achieving industrial quality lenses that would actually interest satellites compagnies.(maybe he did lose his mind?)
Anyway thanks for all the work you put in there and for explaining with so many great details the thinking behind those lenses.
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.
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!
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.
Incredible work, great video, and the performance from such a small monolithic lens has really impressed me!
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! This was the single clearest and best exposition of a technical topic ANYwhere on YouTube!! You are a master, not only of glass but of narrative. Bravo!
awesome to see this series again. Incredible work on this project!
Very cool.
The amount of information is great.
Thank you for your videos.
Much appreciated.
In one video series you taught us so many advanced concepts of optics, light waves, interference, softwares for these advanced niche areas, manufacturing.. Thank for sharing your knowledge and experience with us. I can't possibly dream of replicating any of these but I walk away but smarter than where I started.
This is isanely interesting!
Being an amateur telescope builder myself, I can proudly declare - your content is TOP !
Another fantastic video.. Thank you for sharing your incredible knowledge with the world. Absolutely fascinating! 🙂
This has been a truly outstanding series - wonderful
Thank you
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!
There's a super-absorptive coating out there called VantaBlack that might help with the contrast. Still, flaws and all it proved to be a very capable little thing - a single piece of glass - very impressive. Polishing really is quite the art.
VantaBlack isn't a paint as much as it's a coating process. It's also extremely fragile. I do believe it was invented for applications like this, though! There's an acrylic paint called "Black 3.0" by CultureHustle that gets very, VERY close to the darkness of VantaBlack which I know a lot of people have used for telescopes. :)
O*U*T*S*T*A*N*D*I*N*G A*G*A*I*N Sir, you are without doubt, an International Treasure! Your work in creating these videos, coupled with your incisive, intelligent narration, seasoned with a very unique and Extra-Dry sense of humor, has resulted in a library of Matchless Value! Bravo! Long life, fair winds and more power to your elbow.
Nice video, excellent explanation, absolutely astonishing results considering you are a pioneer in building such small monolithic telescopes. Congratulations and keep up this nice 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.
Great video. I think it just goes to show that at the end of the day, when you're hand-making something, maths can get you so far, but it's the more macro level things like the brand of black spray paint you use that will end up having more of an impact on final image quality than a few nanometers of precision.
Applied Science - 2022-06-11
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?
Huygens Optics - 2022-06-11
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.
David Lindes - 2022-06-11
@Huygens Optics 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!
Curly G Cradle Rock - 2022-06-13
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.
David Lindes - 2022-06-13
@Curly G Cradle Rock haha, indeed.
T. Joseph Nkansah-Mahaney - 2022-06-15
@Curly G Cradle Rock Ooooh.....so did you order one too?