70-200mm Focus Issue

[dlthibo]

Well I just discovered something interesting by accident. I just tested the focus on my 70-200mm f2.8 lens on my new 7DMKII. I found if I turned the manual focus ring CW before calling for the camera to autofocus it was spot on. However, if I turned the manual focus ring CCW before calling for the camera to autofocus it missed focus. Is this normal?

[ebiggs1]

I never noticed that behavior.  But I can't say I really put it to the test.  On my 1D Mk IV with my EF 70-200mm f2.8 L II, the focus is very fast and very accurate.

[RobertTheFat]

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@dlthibo wrote:

Well I just discovered something interesting by accident. I just tested the focus on my 70-200mm f2.8 lens on my new 7DMKII. I found if I turned the manual focus ring CW before calling for the camera to autofocus it was spot on. However, if I turned the manual focus ring CCW before calling for the camera to autofocus it missed focus. Is this normal?

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Generally speaking, lenses that allow manual override when autofocus is active (and I believe that includes all Canon "L" lenses) expect the manual override to come after the autofocus mechanism has done its thing. You may be confusing your lens into thinking that you didn't want it to re-focus after your manual intervention. So if you use the manual focus ring and then think better of it, try turning autofocus off and then on again before calling for a re-focus. That may or may not help, but it can't do any harm.

[ScottyP]

Maybe it's like that old joke. I guy goes into his doctor and says "doc it hurts when I do this" (bending his arm in some odd way). The doctor says "don't do that then." 😉

[TCampbell]

The lens should focus the same regardless of whether it needed to focus in from infinity, or focus out from minimum focus distance.  

It sounds like you're describing some gear-slop / back-lash in the focusing mechanism.  

I would contact Canon and inquire. 

Do _several_ controlled tests.  Repeat running the focus out to infinity and then auto-focus on something nearer a half-dozen or so times and compare each.  Then run the focus in to minimum distance and let it auto-focus to something farther -- and do this a half-dozen or so times as well.   

You want to know if this is repeatable or if it was just a random fluke.

[dlthibo]

Thanks for your suggestion. It does repeat. In November of 2012 I had to ship this lens to Canon for repair. Back then it was an issue with the image stabilization. When the stabilization was on and I'd try to auto focus the whole image would "jump" in the viewfinder. Canon replaced parts and made the repairs. I guess I'll need to contact them for this issue.