Hi Amita,
I have "tested" the lens several times, with about two or three
samples, both used and new. In short, the lens is very fine from 2.8,
very good from f/4, and very very soft at anything under 2.8. So from
1.8 to 2.8 it acts as a soft focus portait lens (very high levels of
coma, which looks like veil over contrastier edges). At 2.8, it's
very respectable. Other than that, it's a big lens and the hood is
essential to be fitted from what I heard. Also, wide open the real
speed is more like /f2.2 or so, about 1/3 to 1/2 stop less light than
one would think from the 1.8 aperture (somewhat common trait with
superfast lenses, the manufacturer boosts the lens speed in
specifications). So for me, it was an excellent f/2.8 lens which was
usable in _some_ situations at f/1.8
Even more shortly, not a bed lens at all, if you think of it as f/2.8
So if you can get the Pentax, it will be smaller and also more flare
resistant, most probably. I haven't compared them though. The full
aperture on the sigma is only for emergencies ;-) Minding that, when I
was deciding between getting a Leitz Summicron 2/35 or Summilux 1.4/35 (not
ASPH), the 'Lux was usable at 1.4 also only at emergencies - it had
exactly the same fault as the sigma (only somewhat less pronounced) - coma at
full aperture. But it's very hard and costly to make a 20mm lens that
is excellent at 1.8 ...
Good light!
fra
