Mix and match problem...70-200L I 2.8 is great with 5DIII but serious front focus with 7D

Started Oct 23, 2012 | Discussions thread
riknash
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Re: no 'known' or inherent AF prob with 70-200L mk I
In reply to Lemming51, Oct 24, 2012

Lemming51 wrote:

jkf11610 wrote:

I own a 7D which I love dearly....I get great results with the 15-85 EFS and 70-300L (borrowed). But, for Friday night football with poor High School lighting (the school is in a residential neighborhood and needs to comply with light spill over rules) I have to crank it up to ISO 4000 to keep a decent shutter speed (1/800). Still I get results I am happy with most of the time.

I was recently able to borrow a 5DIII and 70-200 2.8L IS (Mark 1) and I am thrilled with the results even at ISO 6400 (see below). Last Saturday I did a mix and match using the 70-200 lens on my 7D in late afternoon cloudy weather at a Pop Warner football game. Almost every shot suffered from severe front focussing. The same lens that performed so well on the 5DIII and the same camera that worked so well with the 70-300. Something about this combination just isn't working.

Is this a known issue...perhaps I was distracted and had a setting or something else wrong....is it just one of those things? Is it due to the indifferent lighting?

Don't get me wrong...you couldn't pry the 7D out of my hands for anything less than a 5DIII or newer 1D. I'm just trying to understand what went wrong last Saturday

I'm not seeing the misfocus in that (small) example.  Original with larger size doesn't appear to be in your gallery any longer.

Have you checked the borrowed 5D III's MFA settings?  It could be that copy of the lens needs calibrating, but your friend has applied correction via MFA in his 5D III.

I'm thinking its more possible the MFA could only be required on the 7D and not on the 5DIII. It is very possible to have different MFA settings for different 7D copies with the very same lens. Its also entirely possible that a different lens may not require MFA on both 7D copies yet another lens will require MFA. There are many variables at work when it comes to focus accuracy including camera AF unit alignment and lens element alignment.  A zoom lens is further challenged with a possible variance in focus accuracy as the focal length is changed.

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