I have a couple of these lenses. I bought the first one second-hand, for
use with studio flash, since it has a constant aperture, making exposures
very straightforward. It soon became my daily lens (in preference to the
28-200 f3.8-5.6), so I bought a second one, new this time, to be sure I'd
always have one, since the used one was a "high-miler" and the focussing
ring was a little loose.
The picture quality is pretty good (better than the 28-200), and so is the
flare resistance, especially considering that it comes without a lenshood.
There is some barrel distortion, noticeably more than with the 20-35 f4, but
then it's less than half the price of the 20-35.
Mechanically, the new one works perfectly, and the used one has been fine
ever since the diaphragm was adjusted at Pentax Canada over four years ago.
It may seem unimportant to many, but the constant aperture feature matters
to me. I really don't like it when a lens gets darker as you zoom, and when
you know the shutter speed will drop if you zoom in. Maybe I'm
old-fashioned, but I always associated variable-aperture lenses with
low-cost varifocal lenses that shifted focus as you zoom.
Pat White
