Today we're making lenses with epoxy, using a replication molding technique. It... mostly works 😇
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==== Details ====
We can replicate lenses using silicone molds and optical epoxy resin. But there are a lot of caveats to this technique, and little hiccups that will ruin the optical finish. To achieve an optical finish, you need surface roughness and figure deviation in the nanometer range. This means curing temperature and shrinkage become major sources of error.
Residual stress in the molded parts can be assessed with polarized light and a polarizer in front of the camera.
==== Prior Videos ====
Injection molded lenses: • Machining an injection...
Microlenses: • Molding a Microlens Array
==== Materials ====
Mold material: Smooth-On Mold Max XLS ii
Optical resin: Smooth-On Epoxacast 690 clear
==== Analysis Equipment ====
nGauge AFM from ICSPI (www.icspicorp.com/)
Phenom XL SEM from Thermo
Gwyddion for AFM post-processing
Blender for 3D AFM rendering
==== Timeline ====
0:00 Intro
1:09 Replication Molding
3:04 Alternative mandrel material
3:37 Molding and casting technique
4:30 Fabricated lens examples
7:26 Molding priorities
9:38 Molding materials and considerations
10:49 Mold release difficulties
14:30 Shrinkage difficulties
16:04 Effect of Temperature
17:20 Internal stress and polarized light
18:51 Mechanical difficulties
19:40 Alternatives to silicone?
20:40 Direct molding off mandrel?
21:45 Refinement for future work
23:45 Concluding remarks
*Note about the audio* 🚨 Sorry for the noise gate issue! The SEM is in the same room and has two pumps running continuously (diaphragm pump + turbomolecular pump). I cover it all in acoustic material, but there is still a lot of noise to clean up. And apparently I did a bad job this time (combination of noise removal in Izotope and gating in Resolve). Apologies for the audio discomfort! I edit with headphones on, but probably went numb to it after a while and didn't notice. Luckily, it should improve soon... the SEM is moving to a new room in the near future 🙂 *Addendum* It seems I overstated how hard it is to grind and polish polymers! Several folks have informed me that e.g. eyeglasses are mostly polymers these days. I'm not sure what kind of tolerance they hold relative to glass lenses, but clearly it's a mass-produced and probably polished on-demand for each prescription. I suspect it's still a lot harder to DIY good polymer lens grinding than glass though.
I really appreciate the honesty, most creators would just ignore a slight issue like this. Well done !.
Still better sounding than 90% of KZhead videos! :) Just consider making the "release" of the gate/noise remover a bit longer or go with an expander instead and it won't be so noticeable, or even consider layering in some pink or brownian noise (or background music) back after the removal to avoid the total lack of noise. Most noise filters or multi-band expanders/gates also let you adjust the frequency band it works on the most. You can hunt down those upper-mid early reflections that are giving you the most audible trouble with overall less noise removal. Also, never forget the inverse square law: the closer you can get the mic to you and the further you can get it from the noise source, the easier your life will be in post. Likewise, if there is a specific noise source, rather than putting the mic in a traditional spot (e.g. above the head or near the camera), point it so the null of the cardioid pattern (i.e. back of the mic) is pointed directly at the noise source. You're only getting maybe -6 dB rejection on the side of the mic in the traditional arrangement, but in the null you might get -15, -20, even -30 dB through most of the audible band on a small diaphragm condenser.
If you layer a long piece of just noise floor audio from anywhere (doesn't have to be your lab) put it under your audio at like -40db to -30db it'll remove the jarryness of the audio cuts.
Great to see that this was noticed, it's a small thing, but it's good to see you care. I really enjoy the videos,
i do not notice it at all, listening through my speaker, even if i try to. As @Sam Gossner wrote, you sound better than many other youtubers.
The definition of "home shop" seems to a bit fluid, but maybe that's just me ;) "making optical-quality surfaces [...] is really hard to do in a home shop, I don't have a single-point diamond lathe." "just sputter some silver onto your glass in your sputtering chamber..." "let's look at this under the SEM / atomic force microscope..." Just joking of course, awesome content, very interesting.
Haha, ok that's fair 😂
I thought the same in those exact instant.
@@BreakingTaps I am just amazed by the quality of some of the home labs out there. TheThoughtEmporium is also quite amazing if it comes to home labs.
Some home shops are better than others!
That's hilarious! ... but I think you missed the point altogether. The point is, that it is a demonstration of a guy who has these things IN HIS HOME SHOP. Of course, that gives us husbands clear proof that the best makers NEED these tools! Okay, I will admit the scanning electron microscope may be a bit pricy, and never in stock at Home Depot, so my wife can better justify a SawStop tablesaw with less bickering.
hmmm... i did a few things but improved the surface by spin coating the optical elements in a second step with resin. The layer is very thing to the spin coating but finishes the surface to much higher perfection.
Spin-casting should be good for making a reflective mirror. By adjusting the rotation speed you could in theory make different focal length mirrors.
@@peterjf7723 Yes, just by spinning the epoxy in a container, the surface of the epoxy would form into a perfectly parabolic shape thanks to centripetal force.
@@poptartmcjelly7054 I wonder how good the optical would be.
Could you expand on this just a smidge, it sounds interesting. Are you spin coating the pattern/mandrel, the mold or the part?
@@peterjf7723 bubbles might cause a problem with the surface and the uneven distribution of heat within the epoxy might add distortions also but i think it would be fun to see it tried out.
This was very interesting for me. I am a mechanical engineer and usually watch makers on KZhead such as yourself so i am happy YT recommended this vid. As a person who wears glasses and get them scratched in no time, making my own lenses at home would be awesome!
Very cool! The surface finish and actual shape (I forget your actual word for that) look amazing! I have to say I’m drooling at the thought of a diamond lathe for making aspheric curvatures but I’m afraid to look up the cost…
You can probably get a monocrystaline diamond cutter from china fairly cheap, then any cnc lathe will do a good enough job to test things
Yeah, not half bad for such a janky setup! Definitely not going to put Leica or Zeiss out of business any time soon though 😂 I did some poking around and it seems entry SPDT lathes start around 350k USD. It's not as much as I expected, but still a pretty darn expensive single-purpose, niche tool!
@@BreakingTaps Take a look at Huygens Optics channel.
@@BreakingTaps I won't call it cheap but I was expecting, at least, one more zero on the price.
Yeah I was really expecting the same!
You have a great presence in your videos. The lack of BS and depth of technical combined with an accessible persona is great. I look forward to every video, often in topics I didn’t know I was interested in .
@ebrewste I feel the same way, thanks for putting it into words. ...And kudos for the way you did, keeping it short while capturing the essence is not easy, (at least for me:).
Your vids are always interesting, your production quality outstanding and your presentation is spot on. Consistently excellent and one of my favourite channels for all of those reasons!
Loving your content so far. I can see your channel growing exponentially in the near future!
This was such a good, helpful and well-researched video! No time wasted and the extra stuff such as diagrams and putting lenses through polarised light to show the tensions makes such a difference in understanding wtf is going on. Thank you!!
Absolutely loving your content. Keep it coming!
I'm glad you decided to make and upload this video even though you didn't perfect it. Love the video format!
Dude you're the first to do this thank you I was wondering why no one had ever done this I looked it up months ago to see if I could do this myself but no one has ever I guess until now.
Coolest channel! I love understanding these processes that are normally out of reach because they are so industrialized. Not to say that it's easy to create a great lens but understanding the principles brings me great joy!
Spdt sounds really cool, didn't know how those molds were made, this channel is amazing
Thank you so much as always!!! When I find time I will absolutely try this out with some fresnel lenses!
You could polish the lenses before hand to remove some of the imperfections. Then you will want to spin coat a low viscosity mold release to get a smooth surface. degassing the resins premixing will let you degas it better/more gently once it is mixed. If you sputter coat the glass lens with silver as a mold release you could get a perfect surface. Since it has no silicon in it, it wont stick.
What an amazing job! I'd suggest post-curing the ready lenses in an oven at about 85 Celsius before disassembling molds. This is used for ordinary epoxy in order to make it stronger, but in your case it may relieve internal stresses. The post-cure temperature is close to melting point of the epoxy. An another trick may be - create lens with say 95% of the desired thickness. Post-cure etc. Disassemble mold. Then add some epoxy on both sides, assemble and cure, post-cure. Ready. You can try to defeat shrinkage in such way.
You're really thorough and knowledgeable with a soothing voice. Subbed.
I didn't expect this much knowledge and experience from a YT video, this is a paper worthy type of information
Your videos are inspiring. Thanks for doing what you do.
I am not going to make any lenses today but i definitely learned a lot! Brilliant video!!
Regarding stiffness issue, maybe use a CNCed part the is "pretty" close to the lens you want, so the silicone pour you need is just a thin layer. I know you will hit the issue of silicone not adhering to this stiff base, so maybe CNC also some "holes" (|like a mesh), so silicone has a lot of mechanical grab. Really nice that you share the issues you found, I think that is the most interesting part. When things work, those are more boring ;)
Was going to suggest this. Reducing amount of error the silicone can introduce may reduce overall error.
I think this would help a lot! Didn't occur to me at the time, but yeah, some kind of "pre-form" I think would help to both provide mechanical support, and reduce silicone consumption (which also means it would cure more uniformly due to thinner, more consistent layers). Good idea!
i was going to comment that theres no way a CNC he could get would be able to produce a mirror finish but i realized i read the comment wrong. :(
As a bonus, the metal preform should act as a thermal mass and keep curing more even (and could be water-cooled much more easily than a silicone mold, I imagine)
I worked for years in a surface lab lapping and polishing plastic lenses all day. It's absolutely practical
Hmm... i should try this. I've been making deformed lenses from cyanoacrylate. The whole point of those is to have optical quality "blobs". They give uneven ghostly images when used with RGB leds, deliberately breaking the smooth beam. As the RGB elements are slightly off set from each other, each individual led gives its own distorted image. But because they are so close to each other, you get similar shapes, for ex arc where one side is blue, one is red with a green band in the middle. When you slowly fade them out, it animates the image.. Very, very beautiful. This experimentation started from using crumpled mylar as a reflector. It just loses a lot of strength and it is difficult to get it at optimal distance. But distorting the image at the source, i get must clearer image. I add layers of cyanoacrylate, let it drip using accelerator in the other hand to freeze the shapes in place.
Do you have video clips of this? Sounds amazing ^^
Agreed, please share some images / videos / words on the process!
Dang, I need to see the resulting images of this
Bloody fantastic. Thanks for doing this
this channel is a goldmine for people who like people making stuff
Incredible work as always !
Love your content mate. Would be interesting to hear what you do in your day job and how you got started!
such a great channel underrated, thank you for your informative video
It seems like dropping a glass backer on the freshly poured silicon would be a good combo as silicon likes to bond to glass. Also using much thinner silicon pour would reduce flexing with that technique. 3D printed mold walls with surface features to give a mechanical bond to the silicon would also aid in making a more robust mold block along with the glass backer. Assembly and injection features can also be added easily to the 3D printed mold wall. Thanks for sharing your work with us.
I really appreciate your videos! It is neat to see what can be done at home.
This is great information, thanks for sharing! I would add that you can use acrylic resins and optically clear silicone to make lenses. Be careful not to buy acrylic that contains mercury - it's often used in cheaper products to make it clear, and it's toxic when liquid. The refractive index of plastic tends to be lower than glass, so expect the lens power to be different from the glass original. To get around the thickness problem, you could try moulding thin layers of epoxy in an open mould to gradually build up thickness. Then when the lens is almost reaching the other half of the mould, put the lid on and do the final surface with it closed as you would normally. To get rid of bubbles, you can put the entire mould inside a vacuum chamber or use a machine to vibrate the gas bubbles out.
❤❤❤ thanks for making this. Very intimidating!😅
Thank you for sharing!
Hey! Great video! I'm glad you liked the metal coating for mold release trick from the micro lenses video!
🤗
Amazing information! Thank you for your great videos!
The carbon fiber mirror idea is excellent. Thanks for sharing the knowledge you gained with us, for free.
Super interesting, thanks for sharing !
That's a really interesting project! I guess the biggest step is the stress-free curing of the epoxy so that you get rid of the birefringence. (just a small comment: the noise gate on your audio is a bit disturbing when listening with headphones. Don't be afraid of a bit of background noise...)
This is really neat! I may actually play around with this. I actually have some smooth-on silicon and acrylic resins. Would potentially be cool to cast a lens in the inverse of the type you wanted. Say if you wanted a concave lens of a certain camber, just cast it in a convex lens of the inverse camber.
Instead of sputtering metal on to the glass lenses, you could try an oleophobic coating that once applied and then polished off leaves a nanometer-scale fluorine-based layer on the glass. Try talking to Aculon in San Diego. As you alluded to, you probably want to minimize the thickness of the silicone molds and bond them to a steel plate with cooling channels so you can actively cool the parts while curing. For the single-step molding, you can use an optical grade silicone (yes, you can make silicone lenses, I've seen a few very nice examples). A longer runner might help reduce the stress at the gate location. The chromatic aberrations you are seeing are likely caused by dispersion. The epoxy you are using likely has a high dispersion (low Abbe number). The common method of canceling dispersion is to combine high and low dispersion elements (classically this was a flint and crown glass element). Do note that your lens copies won't match the glass originals, even if you perfectly copy the form and eliminate all stresses, as the refractive index and Abbe numbers will be different from that of the glass.
you should try the rotating mold method for creating large parabolic mirrors. observatory mirrors are sometimes made this way. they just have a huge plate that rotates at a fixed rate and they pour molten glass on it. the glass naturally forms a perfect parabola from the rotation, and hardens.
your work is legendary. continue to your successes
So chill, I made one of these for my Rink building maintenance refrigeration engineering book, so I can magnify things around the arena!
Would be curious if you could use a non silica glass, like CaF2 or MgF2 to avoid to silicone/silica bonding issues with the mold and not require sputter coating
Oh, I hadn't even thought of non-silica glass. That's a very interesting idea!
While lenses made from fluorides exist, they are reasonably expensive compared to glass lenses. I imagine the simplest and cheapest way would be to buy lenses that already have some sort of coating, or spin coat and bake them yourself.
Or AR coatings. Some of which might not be too hard to sputter/evaporate so you've got a leg up on that one! (Again, give or take size of pattern/mold fitting inside the chamber.)
@@T3sl4 I mean, the matter of fact is that he actually has the necessary equipment to sputter lenses himself, so what we are all describing are ways to do it if didn't have that.
@@graealex Well, ZnSe lenses are a thing and actually somewhat cheap since they're used for CO2 cutters
Oehhh, instant like. I was waiting for it since your Twitter message. So love this channel. :)
Just found this channel, its gold!
Very much in detail , wow. I accidently landed but loved it and subscribed.
seems like glass would be a good backing material since it bonds to it, and it can be pretty rigid
Hah, yeah I think so! Didn't think of that at all, but dropping a piece of plate glass or similar on top (or even chopped fibers into the silicone) would probably stiffen it up nicely. Will keep that in mind for future projects!
For those who don't have the equipment for chemical vapor deposition, Tollen's Reagent can be used to silver the mirror using a chemical bath.
I am a noob and I know this sounds a bit bonkers - but I wonder about some out of box approaches - thinking about how fresnel work - I wonder if building a lens or mirror - micron by micron, so you can control refractive index and chromatic aberration and internal reflection Is possible in a well appointed home shop. You and Applied Science channel could have a fun go at it !
Might be a bit out of my skillset, but there's some neat work done in this area using two-photon lithography. Basically does exactly what you said: prints them up layer by layer at a small enough scale to avoid aberrations. Check out this paper for example (open access: www.frontiersin.org/articles/10.3389/fmats.2020.586496/full ), they print lenses on the end of optical fibers. Pretty cool!
Sweet! I was just riffing- sounds like I have some fun homework!
@@BreakingTaps The link is broken - love your community engagement, keep it up :)
@@karim1485 Fixed, thanks for the ping!
There are "Solar cigarette lighters" made out of metalized plastics to light your cigarette in the sun. They aren't too bad optically and quite cheap. I tried to make a little spotlight out of one and it worked out great.
Great breakdown. Since silicone adheres to glass, you should use a thick glass surface as a backing on your molds so they hold their shape without sagging. Glass can be pretty stiff so much better than nothing.
I'm so jealous of you on so many levels!!! Thumbs up from Montréal!
Your work is epic !
Full of technical knowledge.
Thanks for sharing. When I saw the first 3d printers I was instantly interested in making eye glasses. You can get the shape, but the surface roughness is far from nano-meter smooth
Thank you, I needed this. Can't wait for the mirror video. I've been experimenting myself with different chromium paints, but it just doesn't reflect enough. Seems I need to build a sputtering machine
Wow I've been looking for this kind of video for about a year. I'm trying to figure out a way to make a cheap spherical mirror with a good optical quality out of epoxy. Haven't started yet but this video will be a goldmine for this project (and I'm hyped for the one about mirrors obviously). One particular detail that catched my eye is the bubble defect at 10:20. Did you noticed how sharp the reflexion are on the bubble spot? Maybe using bubbles can solve multiple problems like: having multiple steps using silicone molds that introduce imperfections or getting a perfect spherical surface since the constraint from a gaz is usually uniform. Unfortunately I think bubbles will obviously be very sensitive to themral shrinking gaz will expand due to the epoxy warming up so it might be difficult to control but this is a nice track to keep in mind.
Fantastic video- super interesting!
There may be an issue with temperature with the larger lenses. Looks like they may have overheated a bit, which causes a wavey and hazy look to the resin. The solution would be a slower curing resin that tolerates deep pours more, but that further increases cure time.
Since silicone bonds to glass, why not use a glass plate as a backer when you're casting the upper half of the mold? Then it would support against sag when casting the lens.
Hi sir, To make a very thick convex lens, use old incandescent bulbs for the epoxy mold. Of course, since I did not have epoxy, I filled the inside with distilled water and filled the its hole with hot glue and closed it, but the outside of the bulb glass bubble is slightly grooved and does not fit well with lens water alone, but I am sure it will become a strong spherical lens with epoxy. You can even split old light bulbs into two pieces, each of which becomes a mold to make a convex lens (flat on one side and convex on the other).
Consider using Rustoleum Mirror Paint as the mold release for the resin; the paint will make a first surface mirror against the silicone, but bond to the resin when you pull it out. I think this will work because the mirror paint makes a striking second surface mirror when applied to the inside of glass. I just don’t know if you want the paint wet or dry before pouring the epoxy in…
Super cool, got a sub'd. I hope you do more lens making in the future.
Love your channel! 🤗
As for the mold release. Have you considered spin coating? I know i show up late to the game. But i figured this might do in future projects. Also, a mold release per se has only the job of preventing the two parts forming any kind of bond. So maybe the commercial mold releases are not the best choice. An (to the processes involved) inert liquide with adequate viscosity and surface adhesion might do the trick.
Absolutely fascinating discussion. Thanks.
Eyyy
I’ve sanded and polished resin, worked quite well. Plastic is harder to sand and polish but not impossible, just more effort and time, if it’s spun on a machine, makes it easy. If it’s spun be could fire polished like glass fire polishing.
I spent some time on a DIY digital microscope and was wondering about improving the ratio of field of view to magnification on top of easily available arducam sensors, so this was very informative. Great organization to the video - you walked me through all the factors effecting the end result quality with attention to alternative materials and processes as well as your decision making process. Outstanding. I hope to make a DIY system to reliably create the lense profile in a diy shop. Thanks for the finishing details on the CNC process. Why did you give up on the injection process?
Absolutely awesome research! Thank you very much for sharing, i would be very interested in the mirror project as well! Keep up the high quality experiments! Not very common on youtube
Thank you!
Super stoked for the carbon fiber mirror video
Fantastic information. 😁
Use acetone vapor polishing or flame polishing, flame polishing is an art.
Thanks for sharing.
That's really interesting! I wonder if after it's ready you could place it in a turntable, with one of the faces up, and then pour some epoxy over it, so the resin will flow all through the surface and the gravity+ centrifugal force will smooth out the kinks
Great video, I might have to try this. Have you thought about resin curing speed? I'm thinking some of the really slow curing resins might produce less internal stress.
could you use heat, to partially liquefy the surface of the lens, to get a smooth, clear surface?
Silicone rubber is used for making statues that are big. The silicone rubber is supported by cast plaster usually after the statue is coated with rubber. Typically like a mask of a face is made. So the surface has a lot of features that the plaster can hold the shape of the rubber. So the plaster casting is removed from the rubber and then the rubber from the cast part. plaster can have cooling tubing. Actually you do not want a high thermal conductor if you can keep the heat generated by the epoxy or low. Even thick parts will tend to have uniform temperature epoxy. To plan the cooling add up the thermal conductivity of the epoxy at a tangent to the surface to the center. Add the thermal resistance of the silicone for it's thickness and then the plaster to the cooling.
Maybe you could purposefully add a lot of internal stress to the lenses to make a Gradient-index lense. They use an optical density gradient rather than normal refraction, so you might not need to worry about surface quality as much? Idk. It might work especially well because you are already working with epoxies and I think you can use a uv resin and cure different parts at different speeds. It might also be extremely hard to do, but could be a fun project.
Hi Zach, nice work. I was wondering what your ultimate goal is exactly. If you want to make spherical surfaces, you should not start with a spherical mold, because then you will end up with an oblate elliptical surface, due to the volume shrink. So for making spherical surfaces, you need to start out with some kind of parabola/hyperbola. By the way, if you want to make epoxy/glass fiber mirrors of high quality (for example for telescopes), maybe reconsider: it is technically virtually impossible. I can mail you a few references if you want.
Ah yeah, that makes sense! Can account for shrinkage by adjusting the shape of the mold first. 👍 Would definitely be interested in those references! I've seen a number of papers in regards to replicated CFRP telescope mirrors and while they all highlight challenges (molding distortion, fiber print-through, differential thermal expansion, moisture absorption over time, etc) none of it appeared to be insurmountable. But perhaps once you consider all those challenges in aggregate it just becomes too hard to produce something optically good enough for a telescope? Definitely going to pretend I didn't read that it was impossible and continue trying though, haha. A guy can dream 😁
@@BreakingTaps I'll admit I have zero experience with epoxy but an idea came to me. Could you cure the epoxy at elevated pressure? I'd assume it would make the final part higher density and maybe get rid of most imperfections making it a feasible technique for optical parts. Could also help with the uneven forces on the mold.
Great to see some favorite optics guys know each other...
To Stiffen Molds -Paint back of mold with a thin layer of silicone an lay on a piece of glass, let cure. /or/ -Use rat wire fencing laid on the back of the mold and paint it on with more silicone, let cure. This should stiffen it up real nice like. +chicken wire has ~3x3cm hexagons (very flexible) +rabbit wire has ~10x20cm rectangles (very stiff but big) +rat wire has 1x1cm squares (very nice) I recommend a mesh type material rather than a solid flat sheet since the silicone wont stick to many things other than itself or glass as stated in the video.
I wonder if polymers can be tempered like glass is to reduce the internal stresses. Another idea that comes to mind would be to use some form of solvent polishing to post process the optical surface. Or perhaps heat can be used to flow the material after curing. Judging by the surface roughness of the bubble that you showed as a defect, you could achieve way better surface finish if you could find a way to refine the surface...
Please Try making Monolithic Telescopes! Awsome content 🔥🔥🔥
I was reading an article yesterday about some guys making lenses using UV cure polymer floating in a suspension of equal density fluid. Having it suspended in fluid counteracted the flattening effect that gravity has on fluid over a certain volume. Wonder if you'd try that technique out and compare.
I managed to get limited success making lenses from epoxy without moulds or existing templates. I used a ring of plastic to hold the epoxy, sealed on the bottom with clingfilm stretched tight. To make a convex lens, add a thick layer of epoxy, seal the top and inject air or epoxy to bow the clingfilm out. Concave lenses, the air or epoxy is removed. I also had limited success injecting epoxy between two sheets of clingfilm to make both sides convex and concave, but gravity distorts them and the lower surface is always more convex than the upper. The only downsides are that they arent hugely accurate, and the clingfilm surfaces are delicate. But they work well for visual magnification, and the magnification can be tuned while injecting or removing the epoxy. Nice video, very informative. I didnt know silicone could hold an optical surface, thought it was a bit grainy...
Very neat idea and nice information! You might be able to make complex lenses that don't currently exist.
i think you and ben would make a unstoppable youtube combo.
Potato.... Really like your stuff. Thanks for sharing!
I guess you can avoid the silicon moulding step and create your own mould by sticking some kind stretchy plastic film (like food wrap) over a container. Then introduce partial vacuum into the container. As a result you will get a concave plastic mould with a smooth surface. And the curvature of the mould can be controlled by controlling the pressure inside the container. With two of these you can get a whole mould in which you can inject the epoxy (if aligned correctly) . You can use small to medium quantity of epoxy in this short of mould as if you use a big amount of epoxy the shape of the plastic film might get distorted due to it's weight. And I assume the plastic should also come out easily. It's worth giving a try.
long video is long so not sure if you are going to cover it but seems like the lenses you have could be used if coated properly to release the item, to make the opposing surface too, like having a .2 diopler of one direction and ending up with a cast lens that is a -.2 diopler lens if that is the appropriate measurement terms if not basically using a convex lens surface to get a concave lens that matches it exactly in a negative aspect. reason this thought came to me is that some times having the exact opposite of the former is needed for proper light alignment like making a true spot light out of a normal lamp, (seems like coating after too makes a good reflection surface XD
Try using: 1 - Low viscousity epoxy 2 - Low exothermic, find one give off the least amount of gas, less mass delta (less heat and less shrink). remember you are turning 2 liquid into 1 solid, so there is a chemical process / reaction, just find the slowest one. Oxygen rich air usually worse, so perhaps cure it in a nitrogen / hydrogen rich environment. 3 - removes some of the chemical heat using a control oven / environmental chamber (to minimize dust and moisture) 4 - Thick section epoxy issue a) what happen if you do it in stages? b) can you not introduce sacrificial area on the thin edge to balance the thicker section in the centre, once cured, just cut off the extra bits at the side. 5 - "pre-condition" (temperature) the silicone tool before injection 6 - any injection can result in air trappage in the mould, introduce air vent channels as suggested in 4# 7 - when making the mould, reinforce the silicone with a mesh backing OR place 2 half of the mould side ways (like edge of a coin on a table) and inject the epoxy at the split. 8 - when making the mould, you can perhaps add control stop feature on both halve of the silicone tool, to ensure a repeatable control stop with the 2 halves. (along with the reinforced feature as in #7)
you could use gypsum (stone or die stone) to make the mold. Find out more about how dental technicians make molds or casts to a microlevel.
Off course you can we used to do it all the time we need to put samples in epoxy for the microscope , we polished them to perfection with diamond paste
Lapping something flat is a lot easier than trying to grind and polish a 3D profile (even simple ones like spherical profiles). Not saying it's impossible, just that it's considerably harder than with glass 🙂
a commenter said even perfect reproduced shape won't duplicate refraction due to RI of epoxy used. If pine pitch has the same RI as optical glass when it is used to glue two elements there must be refractive indexes listed for other hardening organic moldable liquid? I recovered a round 4ft outdoor glass table top with a 2.5inch hole for an umbrella pole: i was wondering if I could slump it over a pos mold OR simply force the centre in and retain the edges to have along focal length mirror? but it seems the surface would still have to be polished right ?
Potential solution... If you take two of the exact same lens, thus, when facing each other, you have both the front and back of the lens with an airgap of any preferred distance. Encase the airgap with whatever material you may like, and fill the gap with epoxy via a syringe. A potential problem with this method would be the degree of adhesion between the selected epoxy and the glass, and if that would require the use of mold release (which we already know causes issues). Just a thought. Thank you for the great video!
Have you tried detergent in water as a mold release for silicone? I've used it diluted a few hundred to one in water. spray on lightly with a plant misting sprayer and let dry before molding. It might not be good enough for your lenses, but its way better than that commercial stuff you used. I've used it to get very gloss surfaces with ogoo molding. As well as the go to thing to stop silicone products sticking to things in building industry caulking. In Caulking you can also use it on your finger to get a really smooth fillet and skin the silicone in one go. Alcohol also works in a similar way but its not great for mold release due to evaporating too fast.
i may say that because i have some of the critical hardware needed for such a project, but it seems more simple to me at least to go the diamond lathe way (i have some xms50-s linear actuators that would fit the job i guess)
After seeing your video on atomically flat surfaces I got an idea to bring this together with the molding of lenses. Assume you use a thin mica sheet as the defining surface in your molding process. You could then get an extremely flat surface. Hopefully the mica sheet is flexible enough to allow some radius of curvature (think of those adaptive mirrors which is deformed deliberately). Mica might need a sputtering step in case it sticks to the epoxy. Viable?