There is no good one out there besides the Canon official for old FD to EF mount lenses. That one also, only works on certain telephotos.
(Note for anyone looking, FDn lenses which are higher quality and newer, can be adapted. Search online for a conversation company)
Im looking to make one that works for all.
Starting from the ground up, working with old lenses, keeping that nice Canon color then figuring out the specifics of it. Calculations, parabolic curves, refraction all that to be able to fabricate it from ordered parts and lenses.
Then once I have the 50mm working, I will make a variable one, one that can be adjusted for any lens telephoto to whatever, with minimal to no vignetting, hopefully no stop loss, and no visual CA like the over the counter inserts.
(EF Lens) Im using 5d Mark II and III
FD to EF Adapter
Off the shelf bad Chromatic Aberration FD to EF adapter.
I have had nominal but promising results using the back piece from a cheap Canon wide to telephoto lens I think a 28-70mm. Pictures in the project. (will post pictures, have both ungraded and graded ones.)
Focus distance achieved between 2-3 ft depending on aperture. No CA as far as I can tell very sharp. (honestly surprised at this.)