Huygens Optics - 2019-09-17
This video is a follow-up from the video on spherical radius grinding. In this video I explain briefly the grinding process (using sIlicon carbide, SiC) and polishing process (using Cerium oxide, CeO and optical pitch. If you want to know more about the properties of optical pitch, this video is entertaining: https://www.youtube.com/watch?v=SkpZAg4RkGI The surface is inspected using a simple Foucault tester made of a smart phone and a razor blade. More information on the Foucault test can be found at: https://en.wikipedia.org/wiki/Foucault_knife-edge_test or https://stellafane.org/tm/atm/test/understanding.html A very good book on optical manufacturing techniques is "Fabrication Methods for Precision Optics" by Hank H. Karow. A good book on optical testing is " Optical Shop Testing" by Daniel Malacara. Gordon Waite has a great series of video's on polishing and grinding of large telescope mirrors: https://www.youtube.com/user/GordonWaite It is now possible to contribute financially to the Huygens Optics Youtube channel. Please refer to the "About"-page of the channel for details.
This is black arts you share with the world. I am humbled someone who knows this esoteric knowledge has kindly decided to share such things in detail on youtube. What you do is pretty amazing, and I may use some of this knowledge at one point in my watchmaking for crystal polishing. Thank you!
Same here, this is extremely valuable, well into the black arts territory.
Unless you’re sticking with mineral crystal, I don’t think this will work as well for sapphire. And unless you’re working on a watch with a very unique and hard to find crystal , I can’t imagine spending hours on just a crystal
@Im Visier you misunderstand watches and watchmaking, where "black polishing" a screw head to a specular finish is mundane.
The process of polishing brittle optical materials presented here is directly applicable to many watchmakers working on older watches or making new ones. Restoring an old crystal, or custom fitting a new one, is often sensible when balanced against the time and money costs of obtaining a replacement, if one is even available.
A watchmaker wouldn't be concerned so much with dimensional precision in polishing, other than it makes work quicker and easier to produce a consistent result. The idea of using pitch or a similar conformal surface helps to this end. Also helpful is the explanation of surface damage and how inspect for it, which doesn't seem to be common knowledge.
Cerium oxide is also used in semiconductor wafer polishing :). when doing failure analysis at the micron level we actually look for Cerium during atomic analysis to confirm if a defect was introduced in a polishing step
In the making if you pass sound waves from furnace to Cut gob the structure is more finally packed with less micro scratches
Ahh this takes me back to my mirror making days. I never ground anything that small though. My first mirror was a 4.5 inch Newtonian, then a 6 inch and then an 8 inch. It's a very time consuming tedious process especially figuring a Parabola on a Newtonian. We sometimes had access to Pyrex Glass but my 8 inch was regular glass and I had to wait 2 hours for the mirror to cool down after polishing before I could even test it with a Foucault Tester
Slowly working through your videos, just wanted to say thanks! They are fascinating, keep up the great work!
Very interesting! I found your channel from your DLP video, and it's been fascinating to see how just hand polishing can achieve such smoothness.
It’s always so interesting to me how such simple things we take for granted in life have had so much time and effort put into them. Great video
At the end I wanted to scream hysterically non-stop! I SINCERELY think this is really incredible and amazing (honestly!!!) but if I had to do it myself I would rather bite my own head off! You deserve congratulations orders of magnitude greater than I could conceive in words! Just... amazing.
One of the most interesting channel I'v find in years. Thank you so much!
Interesting work! Is it a personal preference to grind these by hand, or is (partially) automating it very hard to do?
Thanks for posting this! I'd love to see how you add the reflective coating. Hope you make some more videos. Thanks!
Your video reminds me for making my first mirror years ago. You give me confidence to try again. A very rewarding process. And something to enjoy. Thankyou.
This is fantastic, really super that you mention approximate times for each step, and really awesome hack with Cell phone there for knife edge test + great illustrations and ACTUAL values for things (which is super helpful) ~ Looking forward to learning more [Thanks for making these videos ! ].
Now I understand why high quality optics is so expensive.
@Laharl Krichevskoy How much would such a machine with competitive results cost?
Really interesting. Im moving to the mountains of spain soon and i’d love to make a small newtonian scope. Looking forward to the mirroring video. Cheers julian
That is exactly what I want to make. What emitter are you using? Osram or Cree? Are you making your own driver too? I love the Anduril UI. The FET drivers are good for high amperage but need a lot of heat sinking. I hope you post more on this, would love to see details.
This was extremely informative. Thank you very much!
Extremely well explained.
What I was wondering is: where do you get your raw grinding surface from? I mean the one that already has the right radius on which you're grinding the your glass mirror.
Initially both surfaces are flat, but through a special grinding method and using abrasives with large grains, one of the surface becomes concave and the other convex.
This is a wonderful tutorial, thank you
This is absolutely fascinating. By pure dumb luck and no craft, I managed to polish out fungus lines from an internal convex element of a Cooke Speed Panchro lens without destroying it. The lens was full of fungus and had been written off as uneconomic to repair. Had I known its history, I would have given it more respect and handed it off to someone else who knew what they were doing.
I hate to ask a question that has been repeated before but if I'm interested in learning to make my own lens, do you have a video or know of a video that shows how to source these materials?
This is really excellent. I have a question. I have a telescope eyepiece in which the coating on the outermost (field) lens is deteriorating. I want to completely remove the coating so that the appearance will be uniform across the field instead of darker where the coating is missing. Can I accomplish this by pressing the lens into styrofoam and then using polishing compound with light pressure on the lens against the styrofoam? Thanks!
Amazing channel. Is this how microscope lenses are made as well?
Does it become a more standart process, if you use ultrasonic waves to make thrill up abrasive particle within solution?
Hello, very interesting video, thanks! Can I ask if you have done any irregularity/power/flatness measurements (with an interferometer) for such hand made items? What levels can you reach?
Hi Tomas, I did do interferometry on small mirrors (not this one by the way, this was just for the demo of the process). So, if you put some time in it and avoid the pitfalls related to temperature (friction/warm hands) you can get down to 1/8- 1/10 Lambda. As you can see at around 11.05 , there is some irregularity in the surface. This is due to pressure and can also be largely avoided by milder polishing in the final stage.
What about grinding a optical lens? Is 1200 still sufficient as the finest grain size?
Hi Jeroen, Fantastic channel. I wonder, could you give advice on where to buy small glass blanks like these. I'm interested in getting three BK7 blanks, size is not critical (maybe 35-40mm dia 14-16mm thick) . Can you give any pointers? I'm in the UK. All the best Matthew
1:02 regarding subsurface cracks. Extreme hazard considerations aside, I wonder if either grinding with hydrofluoric acid or pre-soaking the lens with HF, for some soak-grind-(wash) time cycle to be experimentally determined, might reduce crack propagation by loosing up/freeing up the glass surface "bits" (not sure exactly of the microstructure of glass) so they would break off more easily and not transfer force into subsurface layers and induce cracks. Has anybody ever tried that (and lived :))?
I'm sure that you could etch the subsurface damage away if you etch for a long time (it's a relatively slow process). However, the fastest (and safest ;-) way to remove it is just to use sequential grinding and polishing steps.
@Huygens Optics thanks for the reply. I meant less about etching away damage after it happens and more about preventing it altogether--improving the grind process itself by (maybe) allowing more aggressive grinding with less subsurface damage, if the HF could somehow "loosen up" the top layer of glass. So the glass bits would break off more easily and (maybe) not cause forces to propagate down into the glass as much.
@perspectivex Aha. Well, I'm not sure how that would work. The loosening of particles from the surface is actually the result of crack propagation in the glass. Anyway, I would never try to attempt grinding with HF as an additive to the SiC slurry...
@Huygens OpticsI'm not going to try it either... I'd like to keep all my finger bones.
...do people ever grind their own mirror flats for star diagonals? I can't find anyone doing that but I don't know why not.
I can’t imagine the difficulty making the mirrors for the JW Telescope must have been.
I would have put the glass in a drill, and rotate it at higher speeds, with less friction. Causes smaller cracks, while still allowing for fast work completion.
Can you aluminize a ground blank and just polish the aluminum? Maybe you'd need to re-aluminize but it seems like it might be easier
Aluminium is actually way more difficult to polish to optical quality then glass.
Excellent, again! Congratulations!
now imagine how the biggest telescope which is about to be put in space was made and why it is so expansive and why it took so much time... James Webb I mean
Hello. How hard is the pitch you use?
I have some lenses to polish. The soft has several grades of hardness.
I generally use the medium grade Gugolz pitch. Since temperature is an important parameter, you can still vary the hardness a lot by polishing at a different temperature. For making spherical surfaces, the pitch should preferably not soft.
Love this channel! Now I'm hooked on this post apocalyptic garage made ultra precision cyber {possibly crypto} optic thing.
I learnt more from this video than 1 semester of school
I don't know why I look at this. But it's new and refreshing stuff to learn for me, so I'm going to stick around for a while.
I got that Pitch some cerium oxide, pitches love cerium oxide 😂 jokes aside, I love this channel now that I’ve found it. I love honing surfaces of things in my free time. I even have a pc a honed the surface area of the cpu and heatsink, then honed the heatsink to the cpu (to mostly accommodate for any convex/concave surfacing that may have been introduced by my lack of skills to either the die or the heatsink) and tested it with and without thermal paste and all cores run cooler without the thermal paste and I did long benchmarks and rarely saw over 45 Celsius on any core with a very modest, stock aluminum air cooler. Now this isn’t a ryzen but it is a amd “A” series, I can’t remember exactly which, but I still use it, as is, for CAD design and software testing and never had a hiccup.
You should make a video about Holograms, that would be cool
Interesting, thanks you!
what temperature for the pitch ? where do you get the supplies ? Thanks.
Generally you use the pitch at room temperature, so let's say around 21 deg. C. There are different types of pitch which have a different melting temperatures. This influences the "hardness" (viscosity) at room temperature. The type of pitch you want to use is dependent on your surface. Generally, you use softer pitch for a-spherics. Since I am in Europe I orderd at a German Company named Pieplow & Brandt. However if you search for "optical pitch suppliers" you will probably find a supplier in company.
Thats funny. Long ago a had polished a 135mm spherical newtonian mirror. But i was not succesfull in the job and sadly i had gave it up. Now i want to try to polish a flat one. Can i use this method for polish a flat by hand? I worry about turned edge. What kind of tip you give me to succesfully complete the work? Thanks
where can I find all these materials?
do you polish again after adding a reflective surface?
No, all polishing and figuring is done before coatings are applied. These processes remove material, so you'll only be removing the thin coating you just applied if you attempted to polish after coating. Sorry this is 3 months late, but I hope it was helpful either way.
Bedankt U motiveert mij weer.
How do get the surface curvature that you require. You impressed the blank on the pitch but the blank doesn't have the final surface. I don't understand.
Will using your hands as point of contact for shaping the curvature trough any chance of give a person to getting a good measurement. thanx a bunch. highly education.
Very cool!
Lol just watched your oled video and then went on a tangent researching mirror grinding and here we are again haha
10:40
Where can one person find the lens holder mechanism shown holding the small lens?
Thanks
This thing is sort of an antique, I got from an astronomy club that were throwing stuff away. So, the best advice I can give you is see if you can find something similar on ebay. Look for "self centering lens mount".
Andrew Moore - 2021-06-26
I can’t see myself ever needing to do this - but nevertheless, it’s always great to see a master of their craft at work. You have amazing skills and thanks for sharing them.