[09:05] Considering that most VR and AR systems today... actually basically every one I know of (even the Meta prototypes) have PPDs well under 80, I'm thinking that I should be more cautious with my optical path. This was brought to my attention when I found out about this AR lens module:

It's also notable that it's up to 25% transparent in this industry. Perhaps that means that I could use a R60:T40 beamsplitter instead of a 50% splitter.

Anyway, I'm still unconvinced that the fresnel lens is going to give me the optical quality I desire, so I went on AliExpress.

Hm? A lens in the 50 - 60mm diameter range that has a usable focal length? ASPHERIC TOO!? Wow that didn't take long to find!

Then I found a bunch of achromatic lenses that all had rather high focal lengths for this application. I also found a parabolic mirror, but the simulation didn't reflect light like I hoped it would (90 degree reflection + focusing).

This lens looks suprisingly good in the AliExpress listing video for being 20p per each. I've assumed the actual optical diameter is 34mm because it looks like there's a bit of a flat section for mounting, though there's also a youtube vid that looks to be an edge-to-edge lens:

A solution seems to exist for 1x 60mm + 3x 34mm lenses, though I still have the unsimulatable problem of chromatic abberation to worry about. Hopefully, the longer the focal length the less of an issue this is. It's also going to be a very tight fit with that 60mm diameter lens, and I'm using the outer reflective surface of the 20mm prism instead of TIR like in the previous optical path. (The 200unit ruler on the mirror also implies where the glass face is.)

[15:50] It's interesting that AliTools only has historical data for both lenses that only go back 1 week. Is the reason why I never found them before related to the part where they never existed until very recently? I also noticed that the lens is F45mm not F47mm as I thought in the simulation. I doubt it'll change much. (Can confirm. I was able to move the screen forward 4mm though.)

[Feb 2 at 02:33] Me: Wrapping things up and about to buy

Aw the exchange rate went up? Wait. F100mm? 

checks bottom of basket

clenched teeth facepalm

Second time I've had a solution and then got hit with Out Of Stock. I'm guessing in this case it was a listing error.

A solution... will have to be recalculated.

 I mean... this lens I found from the same seller still exists. It was in my basket and I was about to remove it.

nvm now I remember why I was supposed to remove it from my basket.

A solution... still has to be recalculated.