[derAngler]

Hello,

how good is the performance of your 150mm 2.8 FA lens on a 645D, especially at f/2.8?
My copy of the lens is pretty good from f/4 to f/13 in terms of sharpness. Only at f/2.8 the lens performs mediocre. At this aperture it produces pretty strong chromatic aberation and the sharpness is also very soft compared to the other f-settings. Also the profile for this lens in Lightroom 3 doesn't remove the chromatic aberrations. Only the vignetting and some distortion is corrected.
Unfortunately I cannot compare the lens with another 150mm.

dA

[rlj]

My copy seems very good at f2.8, but decidedly better by f3.4. One issue to check is if focus plane of your lens is off, and this error is masked by the increased DOF at smaller apertures. That is, your lens may need focus adjustment at f2.8. When I want to shoot 'wide open', I do it at f3.4.

Most every lens made is only centrally sharp wide open (soft edges) and also has lower contrast. These imperfections diminish with stopping down, being optimum for most all lenses about 2-3 stops down from wide open. Rarely are lenses diffraction limited wide open. (I can think of one in particular by Leica: the 280/4 APO---was sold for around $4000; this is seen on the MTF plots as decreasing MTF as lens is stopped down from wide open.)

The whole issue is simple optics vs cost; Pentax lenses are not that expensive. The digital sensors magnify these imperfections (less of an issue with film, also masked, but by film's limitations). Even my copy of the Pentax 645 600/5.6 is better at f8 than f5.6, despite it being a rather expensive lens. It is still not diffraction limited.

[spacevoid8]

This is very good lens, complete satisfaction, a have one. Here is some random fast-shoots from island Crete (except first one - it is my homeland - Russia). On last photo you can see picture of me at f2.8 All other pictures made with f10, f11. Samples will be available for 30 days.