AF Microadjustment

Having recently found that a couple of my lenses are front-focusing, I just spent some more time calibrating them using the excellent LCD moiree at Northlight Images. Having previously tried to do it using Live View and failed - it's very difficult to compare settings in a scientific way like that - I decided to go back to taking one image for each setting. That was much more successful.


But I also noticed that the moiree patters are much easier to compare at f/3.2 than at f/2.8. At f/3.2 they clearly pop in and out of focus, and finding the correct setting is quite easy - whereas at f/2.8 the difference is very hard to see. Even when correctly focused the outer moiree rings are barely visible.


I guess the depth of field is just too narrow, and the difference in focus at different points of the lens too great, for the patterns to show up.


I also noticed that the moiree is most visible when the images are certain sizes on either the camera or computer screen (when viewing the photos of the moiree, not the original). If I fill either screen with the moiree photo then the pattern doesn't really "pop" like it should. But when fairly small (25% of the camera screen and maybe 5-10% of the PC screen) the patterns, and their differences on different AF adjustment settings, are clear to see.


Has anyone else found this? I think it's worth noting as I spent ages trying to check my lenses at f/2.8 and think I basically wasted my time.