Re: Pentax 16-45/4 or Sigma 18-50/2,8

[David Oswald]

All this talk about the 16-45/4 and Sigma 18-50/2.8, I've got to weigh 
in with my findings too.

I owned (past tense) the SMC Pentax-FA 20-35mm f/4 AL, and now own the 
SMC Pentax-DA 16-45mm f/4 ED AL.  For about a week I had the two both at 
my fingertips.

Here are a few things I noticed.  At 16mm, the 16-45 has more barrel 
distortion than the 20-35 did at 24mm on a 35mm body.  As a matter of 
fact, the 20-35mm, on a 35mm body seems to have less barrel distortion 
even at 20mm than the 16-45 has at 16mm on a DSLR.

Sharpness is virtually identical.  I've seen some people comment that 
the 20-35 is sharper in the center, and the 16-45 is sharper at the 
edges.  I haven't seen this to be the case.  I do have one shot taken at 
16mm where there is a really bright shiny metal object with a shiny edge 
at the top left corner of the frame, about six feet away.  Under that 
harsh condition I saw some significant CA, but have never been able to 
quite replicate it since.  It may have been more a product of in-chip 
blooming than lens induced CA.

Overall I'm very happy with the 16-45.  ...happy enough to sell my 
20-35, in fact, and that used to be my favorite lens.  Yes, it is rather 
bulky and a little heavier than I would like, but its results are 
outstanding; good enough you'll forget you shot the picture with a zoom.

The difference between f/4 and f/2.8 is exactly one stop.  I'm not going 
to say that's insignificant.  Obviously if you're hand-holding a shot at 
1/60th and f/2.8, you'll have a little more difficulty getting the same 
shot with an f/4 lens.  But on the other hand, with digital it's always 
easy to kick the ISO up a peg, and the results aren't going to be as 
frightening as if you selected a high-ISO film, from what I've seen.  I 
like fast lenses, but an f/4 zoom isn't a bad alternative.  I'd hate to 
imagine the size of an f/2.8 16-45mm zoom. ;)

I've now used my 16-45 for nearly a month.  Sometimes it, along with a 
28-105 will be my only lenses for the day.  You know, one thing that has 
surprised me.  I thought I would miss 20mm on a 35mm body.  But the 
16-45, which on a DSLR is not as wide as 20mm on a 35mm body, seems to 
be wide enough that I don't miss my 20-35 on 35mm film.