Very old Sigma lens works on recent Canon camera...

[Epicuros]

I have a very old 400mm / f5.6 APO lens that I used with my EOS 5 film camera. I had tried it with 300D, 5d MK II, and my latest 5D MK IV, but could not get it to work. However, I could occasionally take a couple of shots and then I was getting non-communication messages! Then I had a "flash": I set the aperture at 5.6 and switched to manual mode and manual focus. As long as the aperture was 5.6 the lens would work without any problem. Then I tried Av mode and set the aperture at 5.6 and it worked. I switched to auto-focus and this also worked.

Conclusion: As long as you keep the aperture at the lens max. aperture the lens works. Obviously only on manual and Av modes. Tv is out of the question.

Try the trick on old Sigmas that you may have.

[baillieswells]

I have not quite so old Sigma 170-500 mm APO DG lens (dates from my EOS350D). It focuses extremely rapidly on my M50. Similar to my EF 300mm f4. ISM L lens.

[Epicuros]

I have not quite so old Sigma 170-500 mm APO DG lens (dates from my EOS350D). It focuses extremely rapidly on my M50. Similar to my EF 300mm f4. ISM L lens.

Mine refused to focus, so I gave it to a friend who shoots only on manual. Thanks for your input.

[El Sid]

I have a very old 400mm / f5.6 APO lens that I used with my EOS 5 film camera. I had tried it with 300D, 5d MK II, and my latest 5D MK IV, but could not get it to work. However, I could occasionally take a couple of shots and then I was getting non-communication messages! Then I had a "flash": I set the aperture at 5.6 and switched to manual mode and manual focus. As long as the aperture was 5.6 the lens would work without any problem. Then I tried Av mode and set the aperture at 5.6 and it worked. I switched to auto-focus and this also worked.

Conclusion: As long as you keep the aperture at the lens max. aperture the lens works. Obviously only on manual and Av modes. Tv is out of the question.

Try the trick on old Sigmas that you may have.

I have the same lens (and a couple or three more Sigma's of similar vintage) - the only digital body it works on fully is my old D30, attach it to any later model and it's full aperture only. The same is true of the other lenses.

Somewhere around the D60 or 10D era there seems to have been a change in lens communication protocol and cameras with the later protocol suffer from the aperture issue - I even have a film camera, an EOS 30, that has the same problem.

[Epicuros]

I think it is typical for old Sigma lenses (perhaps other third-party lenses too) not to be compatible with new EOS cameras. If the time span isn't too long Sigma retrofit their lenses to become compatible, but after several decades they cannot do it. I wonder what Canon does to their lenses to make them eternally compatible with their cameras! I currently use a Sigma 12-24mm that I purchased about 20+ years ago, which, miraculously, works perfectly with my 5D MK IV. This is my only non-Canon lens and there won't be another, considering my age and ...life expectancy! :-)

[El Sid]

I wonder what Canon does to their lenses to make them eternally compatible with their cameras!

It's probably not the lenses but the camera... I would imagine that the firmware includes all the communication protocols ever used with EF lenses so the bodies are back compatible as far as is possible though judging by my 80D some of the latest AF features/focus points are possible with earlier lenses.