[Guest]

Just curious about what happened when Canon switched from FD to EOS. In particular, I was wondering about the flange distance, where FD was 42mm compared to the 44mm of EOS. Did they say why that change was made?


44mm is still relatively short compared to other current full frame compatible DSLR mounts. Sony are at 44.5mm, Pentax at 45.5mm, and Nikon at 46.5mm (values may be rounded).


I have a converted FD 50mm f/1.2 and it is annoying that when used at distant focus, the mirror hits the lens rear! I have heard of some people shaving their mirrors, but the lens isn't worth it for me.

 

I don't know why they changed the flange distance. Given that other companies have longer distances, there  must be mechanical reasons to make the distance not too short, i.e. size of mirror of course. I still have an A1 and several FD lenses. I remember when doing macro with the 100mm macro and several extension tubes, or the bellows, that there was significant vignetting in the viewfinder, i.e. the mirror was not covering the whole light path in that situation. Perhaps Canon increased the mirror as part of the redesign to give better viewfinder coverage? I guess I could have a look to see if the A1 mirror is different from an old EOS film camera.

 

Another thing to investigate is whether advances in shutter development required a bit more space for the shutter?

 

Lastly, the AF system behind the mirror had to be added, although that seems unlikely to have added to depth.