According to Photodo, the F lenses often yield higher mtf values than the FA versions with the same optical formula. We do not know why this is. In a couple of instances the FA lens is apparently better.
I have considered the FA 135 f2.8. The F version, however, rates better on Photodo. Looking closely at the numbers, the main difference is that the F is sharper at f2.8. Why? Anyway, if I decide to get one, I will look for a used F 135.
Joe
