Advanced AF Frustrations: does your 7D Zone AF front focus vs other modes?

Started May 8, 2012 | Discussions thread
Dale Buhanan
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Re: Advanced AF Frustrations: does your 7D Zone AF front focus vs other modes?
In reply to katman68, May 11, 2012

I had one other thought you might want to explore, katman. I noticed that when I was testing out this hypothesis with my own 7D there was a small but noticable focus drift, I'll call it for want of a better word.

I was alternately using contrast detect in live view, and phase detect to compare any change between the two modes with the different numbers of focus points... single, point expansion, zone, etc. I iknew that contrast detect read optimum focus directly from the sensor, so it was the gold standard, while the phase detect mode would be subject to whims of the focus system and any drift, and potentially suspect.

What I noticed was that both modes seemed to drift a little as the camera warmed up -- this based on watching what the lens distance scale did. I saw the scale slowly creep as the camera warmed up. However, all modes continued to track each other, although there was variation on the distance scale from when I first started. The camera was still in focus according to live view contrast detect and the photos were sharp. Make any sense?

So, if you were to do the single point checks you did, and then the zone checks you could see variance if the camera warmed up, unless you went back and reconfirmed the single point again with the camera warmed up. ie., I could see focus drift with operational temperature, but it tracked across all focus modes. The drift was small, but measurable. Anyway, for what it is worth. Hope that does you some good....

katman68 wrote:

You're probably very right, Dale. Even if it seems a bit odd, since the camera has never been even lightly bumped. I put some urgency on more testing to confirm what IS going on today. Now, I just have to go thru and review the shots!

Thanks for the well wish. If it goes in, I might as well send 2 lenses in for calibration too. Hearing the horror stories I dread the bill, but had great service from the NJ service ctr in the past.
Cheers,
Mark

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kind regards
Dale

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