Originally posted by bobbotron Care to elaborate why this style of lens is better
Apochromatic lenses tend to have better out of focus rendering due to the heavily reduced amounts of chromatic aberration: both in the plane of focus, in front of, and behind it. I work with the The Leica-S-APO-Elmar 180mm f/3.5 on my Leica S2 and is a superb portrait lens. If pentax could make, say: an Apochromatic 135mm f/2 ED for the 645Z - that would be an excellent competitive option to have for portraiture.
A few modernized leaf shutter lenses wouldn't go astray either.