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Small range of refractive index, high coefficient of thermal expansion and poor optical properties I have seen plastic lenses on aliexpress, they have poor quality but low price

I'm in the same boat as Google. Not really something I know how to do.

@@stephenremillard1 ok, thank you.

@@j.w.8663 I wish I could be more helpful. Your question did stir up a memory for for me, though. When I was in grad school I had some microwave measurement questions, and I contacted someone at NRAO (National Radio Astronomy Observatory) who was very helpful. I even went to visit since I was close. It impressed me how eager these guys were to be a resource for a student. I'm going to guess that there is well-established know-how for your specific question that resides squarely in the radio astronomy community. I don't work in that field, but it does have a wealth of knowledge about microwaves, the sky, noise, etc.

Using two glass types helps to keep the outgoing angle and height the same for all wavelengths. But as I found, it isn't perfect. You certainly can use two prisms of the same glass type, which just means a little more variation with wavelength in the outgoing angle. Using two different glasses doesn't affect the beam quality for monochromatic light, but it does help to keep all colors on the same path if the spectrum is broad.

You are right. What is written is correct. Thanks for pointing that out.

This is a really good question. Wavefront aberration coefficients can be computed analytically through fourth order aspheric. But for higher order aspherics, ray tracing is exclusively used to understand the final image locations. A fourth order aspheric will cause a small departure from a spherical surface, unlike the higher order terms in the surfaces used here. As you noted, the distortion is hybrid, meaning that there is a change in sign moving from the center to the image edge, and ray tracing, rather than a single number such as a Seidel coefficient, is the only way to look at it. Zemax, and all other programs, do compute a table of Seidel coefficients. But when higher order aberrations dominate, and high order aspherics are used, I really don't know what meaning, if any, they have. I'm sure they are meaningful, and maybe someone can help us out here. By the way, you can get hybrid distortion without using aspherics. Some lenses balance out the third order distortion leaving higher order field dependent magnifications that can result in a wavey distortion versus field plot. Bear in mind that a distortion plot is not the result of only the third order polynomial term, but of all polynomial terms that describe a displacement in the chief ray.

​ @stephenremillard1 thank for great explaination, I did some experiments in cooke triplet lens structure and realize that distortion's magnitude is really hybrid through lenses but in another lens structure, it not really working that way, when the system get signigiciant magnitude on barrel distortion, I add into it another got barrel distortion lens and the final result make the distortion decreased but image smaller, this is quite interesting, the image is really compressed to expand FOV with lower distortion. But I still dont know the way it works.

As much as I would really like to say that you can master this craft by watching my RUclips videos, that probably won't do it. So, you are right in looking for resources. I think it's critical to engage, use software, follow guidance from knowledgeable teachers, and collaborate with a cohort. After all, expertise only comes with a lot of practice. There are courses at UDEMY, CourseEra, UC Irvine DCE, and others, and which is best depends on your background (science, art, etc) and where you want to go with this knowledge (lens design, photography, etc.).

@@stephenremillard1 Thanks for the response I will check them out. While I do have a stem (biochem) background did cover maths and physics, we didn't touch on optics a whole lot. I am a hobby photographer and microscopist, lens design is something that interests me and understanding it surely will come in handy as well. I subscribed to you, I'm sure I can at least pick up some things listening to someone so knowledgeable!

Take a look at 3:46. This is the equation at the top of the screen, (n'u'=nu-y*phi). In Line 49, yt(i) is the chief ray height at surface i. uprime is the chief ray angle after the designated surface. So, uprime(i-1) is the chief ray angle incident at surface i, since it is the chief ray angle after surface i-1. Also, the angles are replaced with tangent of the angles to improve the accuracy.

Thanks for raising this question. It's definitely worth looking at if and how the presence of a microlens array can influence the performance of the lens. Although I'm sure that the know-how is out there, I have not looked into this. But you have made me curious about it.

@@stephenremillard1 Actually, I didn't mean the "micro lens", but a piece of flat glass that sits on top and protects the micro lens array along with silicon sensor., and which in routine practice is cleaned when we want to "clean the sensor". This glass is around 0.8-1.2mm thick depending on camera brand.

Ah, thanks for the clarification. Such a glass is usually included as an IR filter and its presence is also taken into account during the lens design. I covered it a little bit in my patent review of smartphone camera lenses ruclips.net/video/1aCXMBP8_3I/видео.html . Out of curiosity, I just now opened the Zemax file for that patent study and removed the slab of glass over the sensor. I adjusted the sensor position a fraction of a mm to the new point of best focus and the focus was good, although degraded from the original design. The RMS spot size increased from diffraction limited with the glass present (about 1.7 microns) to 4 microns without the glass. The MTF dropped from over 50% at 100 LPMM to about 30%. So, imaging is still possible with or without the slab of glass. But if the lens is designed without assuming the slab, the performance might suffer a little by adding a slab.

The micrometer to which the razor blade is attached is positioned in front of the lens. So the micrometer reads the true location of the blade edge inside the beam.

@@stephenremillard1 Makes sense, cheers!

It might be a while before I can make a video that addresses this question. When I do, it will be a video about distortion, which has probably moved from my to-do list to my bucket list, but I will eventually get to it. The reason why this question is best answered in a video about distortion is because for a flat plane of glass, distortion is the only Seidel aberration. All the other Seidel coefficients go to zero for flat surfaces. Although an illustration might be helpful here, the reason why distortion survives the zero curvature condition is that rays shift their height when passing through a flat glass, and the amount of that shift increases with increasing incident angle. Thus, the far fields experience more shift, resulting in barrel distortion. I hope this helps.

Let me know the time stamp and I'll take a look.

@@stephenremillard1 Ah sry, totaly forgot that 15:00

For the cells that correspond to "Aspheric Spherical", the formula is 8(n'-n)a4*(y^4). For the cells that correspond to "TOTAL W Spherical", the formula is (S1_Pherical + Aspheric_Spherical)/(8*Lambda). Dividing by 8 is what converts spherical aberration from a Seidel coefficient to a Wavefront error coefficient.

​@@stephenremillard1 Ok, thank you very much. I thought that for the calculation "Aspheric Spherical" you take the orange part from the formula at 10:38. Is there a reason why you multiplied this part by 8*lambda ? I thought the 1/(8*lambda) only refers to the Seidel coefficient (at 5:25). I see that you multiplied the orange part by 8*lambda and then divided it directly by it again for the total W calculation. The question may sound a bit silly in itself, as it ends up being the same in both cases. I just want to know if there is a specific reason why you do it differently in Excel, as you show in the formula in the video before.

I agree, it does seem quite unnecessary. I would need to go through my notes from this project to find out why I would multiply by 8 just to divide by 8 later. The net effect works out to the equation for W_040 that appears at 10:35. The case of the appearing and then disappearing factor of 8 may simply be because I was using a pre-existing ynu spreadsheet and that's how it was set-up for some other purpose. I probably didn't make displaying the Excel formulas part of this video, although I usually do that, for the simple reason that although the formulas were working, I didn't spend time tidying them up and making them presentable.

just noticed at 8:28 the double angle formula given is wrong, should be cos (2 delta) = 1 - 2 sin^2 (delta)

@@josephbennett82 Thanks for noticing. Fortunately it's just a typo and not some horrible propagating mistake. The form of the double angle formula that I meant to show there is cos(delta)=1-2sin^2(delta/2). The "1-" was left out.

You can Google the patent number, the first hit will be patents.google.com/patent/US3942876A/en

Thank you so much!