One negative thing about both the 85 and 100 USM lenses is the chromatic aberration. You can see it in this focus testing shot with the 85 wide open. The 100 is exactly the same. The squares are each one inch and I think I was about 8 feet away from the focus target which is the black horizontal band. You can see the purple fringing in front of the focus point.
The target is a cardboard 6 foot x 3 foot sewing layout mat that I place on the floor of my studio. I use the studio strobes to eliminate camera movement. I focus on the black band which is simply a piece of friction tape. If I'm doing Micro Focus Adjust, I'll use a tripod.
It is super-easy to find out where your lens has focused and if you take the time to line everything up precisely you can find problems like tilted lens elements that cause zones of blur.
I've had a lot of luck with this inexpensive system. I like it better than the popular focus testing units where the target is only a short distance from the lens. With this big target I can test at real life shooting distances.
Does the chromatic aberration affect my use of the 85 and 100 lenses? No, not at all. It goes away if you stop down one stop. Also, the zone where you get the purple fringing is in front of your subject. What is usually in front of your subject? Air. So there is nothing there to be aberrated, so to speak.
BTW, both the 85 and 100 needed zero MFA.