There has been a few issues using this lens on older EOS Film Cameras. I have just purchased a EOS 10 Film Camera Body Today and I thought I would try the Yongnou before putting any other lens on the camera. I can say The Yongnou EF 50mm F1.8 works great with EOS Film Cameras and their is no issues at all in fact it works exactly the same as The Canon Version. the metering Auto Focus works as it should so I am presuming that The Yongnou is running exactly the electronics and circuit board apart from The Yongnou having 2 extra aperture blades - better for back lit situations ie lights in the dark.I think It is as The Canon version they have copied it exactly
Yeah yongnuo being a brand from China has done well at copying other brands tech almost exactly, the good news with them is they are just a big enough company that their gear is actually good quality for your money. I haven't bought any lenses but I like the triggers quite a bit. I could not justify the pocket wizard pricing when the yongnuo ones also having TTL work about as well for a fraction of the cost.
Exactly before The Lock Down The local boot sale a guy was selling Yongnou EF 50mm F1.8 and The 35mm F2 some flash guns and triggers for ten pounds per item so I picked out what I wanted and checked it was all working with my camera gave him £20 deposit and went to the cash point got some cash and returned paid him and collected my booty.
