Can AF adjustment values change?

Toggerman

Toggerman

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Name
Scott
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Over the last few weeks I've been noticing a drop in consistently sharp results when using my Sigma 120-300mm Sport on my 7DII whilst shooting football. At first I put it down to the increase in ISO but I was looking through some photos from last year's matches and the images at similar ISOs did seem slightly sharper.

So today I decided to rerun Focal and check the calibration and to my surprise it has changed. At the long end it was 0 and now it needs +9 (I ran the test a couple of times and got the same result), and the wide end was -2 and now +1. It would have been first set in November 2014 shortly after getting the camera.

I do treat my stuff rougher than most but nothing has had a hard knock. All of my other lenses are fine on the 7DII and the 120-300 is fine on my 1DX.

So can the AF adjustment values change over time? And if not what could have caused this combo to be out? I thought that once they were set that was it.
 
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This is not gear dependent.

I use three bodies and 16 lenses and every now and then a lens
or combo visits the optical bench, it is routine. Most of the time this
proves useless but it's better to control than stay with a doubt.

The worse to fear is a displaced element in a lens after some impact.

There is an other point: as one gets used to some new gear or gets
more serious about photography (even both), the critical awareness
and expectations will rise.
 
Some pros check/adjust micro-focus regularly to ensure spot on focus before each assignment ... I don't have a definitive answer as to why the adjustment needs reviewing but it's clearly not just the result of knocks/drops. Of course light will also have a great affect on critical focus so different light at different occasions could also be a reason for changes in apparent sharpness :)
 
I check my focus adjustment every 3-4 months and there is often a small change.
 
I went to the football this afternoon, looking forward to trying out the new calibration. After a couple of test shots of the players warming up I reset it back to 0, the +9 setting was well off. I have no idea what happened with Focal earlier, I must have made a mistake in my method (as well as the mistake of not checking it properly after the calibration).
 
The light was good, never went below 1/2000th IIRC, and although it was very gusty outside the camera goes in a fairly protected area. I think I will order their targets, if nothing else it takes another variable out of the equation.
 
Not keen on focal. I either use spider calibration or dot tune.
 
I gave up on focal as I never got consistent results. The problem with focal is you need to have perfect lighting which just isn't available to the majority of people.

I use dot tune now and am much happier with the results.
 
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