Pentax-DA* 50-135mm F2.8 Review
We used the chart depicted below to test the sharpness of the Pentax-DA* 50-135mm F2.8 at its shortest and longest focal lengths, using a variety of aperture settings.
We then proceeded to crop align the images, and crop the pattern in the center portion in order to test for center sharpness. See the results below.
The same procedure was done to gauge the corner sharpness of this lens. The photos below are crops of the corner of the frame.
Based in the images above, we observe:
- Decent center sharpness at f/2.8, center softness is not significant at both extreme ends of the zoom range.
- Stopping down will further increase its center sharpness, with the peak at f/5.6. At f/8 and f/11, performance is comparable to f/4.
- Softness becomes apparent at f/16 and below, due to the effects of diffraction. This affects both the center and corner, as expected.
- Corner softness is significant at f/2.8, specially at 135mm.
- When stopped down to f/4, corner sharpness improves, and at f/5.6, it peaks. Stopping down to f/8 or f/11 will reduce sharpness slightly.
- Performance at 50mm is significantly better than at 135mm, this trend seems to occur at all apertures but the difference is lessened at apertures equal or smaller than f/5.6.
- Purple fringing in the corners at f/5.6 or above and f/11 or below.
We can conclude that overall, the Pentax-DA* 50-135mm F2.8 performs well throughout the range, except at the minimum aperture setting. Only at 135mm and f/2.8-4 is the corner sharpness questionable, but this significant drop in sharpness is very typical zooms in general. In the aperture range commonly know as the "sweet spot", the Pentax-DA* 50-135mm is exceptionally sharp, as expected (around f/5.6). We consider that the sharpness of this lens is well worth its price and that the lens is worthy of the DA* name.
Even through the lens does very well in general, we would have liked it even more if it were just as sharp (or sharper) at the long end as at 50mm.