Sigma lens won't consistently auto focus with 7D but will work with 20D

[small_foot]

I have a Sigma 70-200 lens that works no problem with my 20D.  However, I recently purchased a 7D and it works for maybe 20-30 shots then stops focusing.  I attach another Sigma lens and it focuses without a problem.  If I turn of the camera, reseat the 70-200, re-insert the battery I might get 1-2 shots before the auto focus stops.  I can place the 70-200 on my 20D at any time and it will function without any problem.  I have cleaned the contacts with a pencil eraser which didn't fix the issue.  Thoughts?  The 70-200 lens is around 7 years old

[cicopo]

I recommend contacting Sigma. They may have to upgrade the chip or software in the lens. 

[ebiggs1]

Yes the lens needs to go back to Sigma as it probably doesn't know what a 7D is. They can blast the chip and it will work fine. As a consideration check out the Sigma 50-150mm f2.8. It is specially designed for the 7D and is an outstanding lens.

It lives on my 7D. I wish Canon thought to make this lens in the imagine of their top-of-the-line 70-20mm f2,8 Mk II, but so far they haven't seen a need to.

[bkushy]

I had this exact same problem. I have sent my lens to Gentec as they do the service for sigma in Canada. No charge and they have apparently upgraded firmware etc. No improvement whatsoever yet the lens will work on other camera bodies. Did you have any success with you lens?

[cuda719]

The problem maybe due to a firmware update, August of last year Canon released a firmware revision and some third party lenses started working intermittent. I have seen this my my nephews 7D he had several Sigma and Tokina lenses that worked prior to the update. He ended up selling his Sigma and Tokina lens and purchased a Canon 70-200 and the problem has never come back.