mcoren wrote in post #18467121
It's naive to think that Canon added AFMA as a "feature" to help pros optimize their lens performance. They did it so that they could reduce production costs by loosening tolerances, plain and simple. By adding AFMA, they shifted the burden to the lens buyer to make sure the AF system is properly aligned.
It is a bit more complicated.
Originally, AFMA was intended to adjust sensor calibration issues with respect to the AF system. That was supposed to be a temporary workaround to use the lens until the body could be re-calibrated. Given the scope, one setting for AFMA was all you needed.
But then, users started using it to fix lens issues, which is improper usage because the AF system is a closed-loop and should always be able to converge to optimal focus (wide open).
So Canon expanded the AFMA functionality to have a per-lens adjustment, and now people are happy to use their defective lenses and bodies without sending them in for proper calibration.
Sigma followed suit with their dock, and some marketing BS convinced customers that paying extra money to “fix” defective lenses on your own is a super cool feature.
But wait, you actually have some features in the dock, such as limiting the focusing range... so when you see a bird far away - quick ! reprogram your lens firmware - so it will focus faster on it.