If you have a zoom lens, AF accuracy is not the same at different focal lengths, so test the AFMA at the focal length you usually use and set it accordingly.
Thanks, but what would mean 70 +1, 135 +3, 200 +7
I can only put +1 and +7 but what should I do with 135? This is way to confusing. Theoretically, I can do a test for each and every focal lenght, print it out and change it before the shoot.
OMG, this is way too complicated. I guess for prime lenses it is much easier choice.
Do you know how Canon calibrates lenses?
What are the two distances you chose. What I read recommended is 5x the focal lenght.
If you use a lens like the 24-105mmL at all focal lengths, at the minimum, set it to about 60mm to do your AFMA. If you test it at 24, 60, and 105mm, you can find the best AFMA values for those focal lengths and see if its only a slight difference, or a major one.
For example, notice the two calibration curves for my 24-105mmL. at 24mm, its a +1 adjustment while at 105mm, its a -2 adjustment. Notice that the curve at 105mm is much flatter, so a small change in AFMA makes little difference. With this lens I'd just use a setting of zero and it would be fine at all focal lengths. But, since the 5D MK III has two AFMA settings, one for wide and the other for telephoto, I put in +1 for wide and -2 for telephoto, and it will interpolate at 60mm by using AFMA=0 or -1
With this lens, there was no real benefit from AFMA.
24-105mm L at 24mm
24-105mm L at 105mm