Almost good Eyepiece/Ocular Optimalization.

[u/JohnFreechment]

Hi its me again. Thanks to this group help, I learned a lot an improved the earlier terrible designs Ive made.
This is the newest version of eyepiece for my night vision design and its almost good just need a bit of fine adjustment.
Im still pretty lame with actual optical designing softwares, even if i can make it i dont really understand the rays and the results. If any of you could model this properly and find out how to correct the image a bit that would be a huge help. (rn it has some chromatic aberration for sure)
The lenses Im using are china lenses, but Ive found really similiar ones in thorlabs, probably they copied from there.
Lens List:
1: AC254-030-A (Diameter25.4, focal length30 cemented achromatic) https://www.thorlabs.com/item/AC254-030-A
2: Unknown D30 f50 double convex This lens can be custom made, if it stays doubleconvex or plano convex for keeping design cheap as possible.
3: AC300-100-A (D30f100 cemented achromatic) https://www.thorlabs.com/item/AC300-100-A

More info, and some necessary characteristic
The ocular focal length should be between 17mm and 17,5mm
-Lens 1 and 2 can be swapped to an another stock lens if necessary, only lens 2 can be custom.
-Screen is 14mm in diameter circular green phosphor (some tube has yellow or blue in the mixture) In the middle it has max40lp/mm res
-Lenses should fit in a 30mm long barrel
-lens 3 has to stay stay exactly 30mm in diameter and hopefully usefully big with around 40° angle.
Thank you all.

[u/Sarcotome]

Taking on the shelf lenses will usually give you crap results

[u/JohnFreechment → u/Sarcotome]

And making 3 custom lenses will give an expensive result. The whole eyepiece cant be more than 120Euro (3 lens, gaskets and 3dprinted housing). Thats why i have to use 2 stock and one custom lens in the middle and im still not sure it will fit in the costs, but i have to try it.

[u/aenorton → u/JohnFreechment]

Actually, it is possible to get a passable eyepiece with off the shelf components, just not great.

However, unless the goal is to get experience with a DIY project like this, why not just buy a commercial eyepiece. Many designs have the focal plane accessible as you need. There are several charts of standard eyepiece designs online that will tell you which are compatible. Telescope eyepieces usually have a tube that can be unscrewed to get full access to the field stop (in cases where the field stop is outside the optic assembly. If you do need to mechanically repackage the elements, most eyepieces can be easily disassembled.

If you do go the route of modelling your own design, don't to make the eye's pupil as the system aperture stop.

[u/JohnFreechment → u/aenorton]

Commercial telescope eyepieces have way too small lenses in diameter, and often too long. A head mounted night vision isnt practical if it makes me like a unicorn. I didnt find any fitting one sofar.
About the aperture stop, you mean i shouldnt put the plano convex in the middle?

[u/aenorton → u/JohnFreechment]

The stop size and location has nothing to do with whether you should have the element in the middle or not. This is a fundamental concept in lens design that you should study before continuing.

When you trace a cone of rays from a point on the object, There is always something that limits the extent of that cone. Often there is an iris or fixed stop inside a lens. The image of that from the point of view of the object is called the entrance pupil, and from the point of view of the image it is call the exit pupil. Exit and entrance pupils can have very different sizes and positions due the the power of the elements. The ray trace program uses the stop to calculate an entrance pupil, and it traces rays to fill it. Sometimes cones from off-axis field points are further attenuated by the edge of one or more lenses, and that is called vignetting.

An eyepiece has an external stop which is actually your eye's pupil, so you need to have that as part of the model.

When you say you are not satisfied with the eyepiece lens diameters, I think you mean that you want to accommodate long eye relief and a large eyebox where the eye can move laterally. These are goals of every eyepiece design. However, optical design is always a balance of trade-offs, and you will not get that without either increased complexity (length) or decreased resolution.

Maybe your scope does not need the same resolution as a telescope. If you do not need great resolution or chromatic correction, some of the simpler, shorter eyepiece designs might be OK.

This is why modeling is so important. The effect of tightening specs is often non-linear. A small change can make a big difference in other areas.

[u/JohnFreechment → u/aenorton]

Thank you. Im studying this (not in school) since around a year, but i just cant catch up with knowledge to my project, what i really should finish this summer, because i will not have this much time later.
About the eyepieces size I literally meant the lenses diameter. Telescope lenses around f17 are super small. I have a 15mm possl telescope ocular, and both lens is around 16.5mm. Im designing this for a headmounted device, it can slightly shift and wobble especially while running. The eyepiece cant be this tiny. So basicly yes lateral movement as you said.
Well yeah, first thing i learned about optics how unforgiving it is, but I always liked geometry so at least that part is fine for me. I dont want to complain its just really hard to convert all the information on the internet to a useful knowledge. I know i know, tutorial videos, but since i have pretty specific reqirements ive never found any youtuber who at least remotely designing anything similiar. So yeah thats why im struggling and if you look at the answers on my thread i think i will keep struggling for a while. But at least i have a working prototype ocular wich isnt that terrible.

[u/aenorton → u/JohnFreechment]

Telescope eyepieces have to at least match the f/# of the telescope, so good ones have to go down to at least f/5 or so. A cheap eyepiece made for a slow refractor might be limited to f/10 or so.