09-11-2017 07:43 PM
I use 50x the fccal length, and a tape measure. If you are careful about measuring the distance, you should get the nearly the same composition and framing of the target, no matter the focal length that you are testing.
The light conditions can affect the camera's ability to focus, especially artificial lighting. Take a series of shots, and use the average. If technique is good, than your results should be fairly consistent from test shot to shot. Ignore the high and low extremes, and average the results.
09-12-2017 10:35 AM
You have a $12,000 dollar lens and expensive t-cons to go with it. If you bought this lens new it has a warranty. If you bought it used, in either way, you need to send it to Canon. They will do a C&C on it. This is the only way you are going to be sure it is right. None of this fooling around with focus adjustment is going to work. At the very least call Canon support and get ahold of a guy that actually uses one of these behemoths. Some of their techs don't ! From what you have posted I don't get the feeling you have experience with one of these super teles either. Call Canon and/or get the C&C.
09-12-2017 10:53 AM
Charles, I sent you a Private Message via the forum with my email address. You should see a very tiny envelope icon near the top of the page (it's not obvious) and you can click that to get to your private messages.
09-15-2017 04:24 AM
Sorry Tim been away for a couple of days. I sent you an email with some strange results of checks I did. Also tried sending you 3 images but for some reason 2 of them were returned as undeliverable.