I care little for (and trust less) magazine tests.

I'd have to say that's not my experience at all. I can't say I find CA all that big a problem with any lens, however the worst offenders I own are both digital specific Pentax lenses - the DA 16-45 and DA 10-17. It doesn't bother me with either lens, but it's certainly more noticeable with them than with older Pentax lenses or with 3rd party brands like Sigma.

Probably the first thing I noticed with the 10-17 was the CA - this shot was taken the day I received the lens, however please note that it is blown up a little beyond 100%:




I think if I was printing above A4 with either lens I might have to correct the CA, however up to that size it's not intrusive so I don't bother.

From my experience I think Pentax don't mind if a little CA is a side effect of producing lenses with great colour and sharpness (like the 16-45 and 10-17) and I tend to agree with them, however with the 10-20 Sigma have demonstrated that you can have those without CA.

My goodies are still coming as well - I picked up the Pentax 645 bought with Christmas money yesterday and I'm awaiting an Pentacon->645 lens adaptor and a Carl Zeiss Flektogon 50mm F4 to use with it.

Vic - unfortunately I've just purchased a manual focus 645 outfit (with just the standard 75mm lens). I could be interested in some additional lenses (if cheap!) and the 645 to 35mm adaptor though so please drop me a PM with some idea of prices etc.

I got some cash which I'll probably spend on camera equipment - current thinking is probably a Pentax 645.

The only thing Schneider had to do with those lenses was sticking their badges on them.

The Sigma 17-70 seems to be well regarded and should be fine for the work you're looking at. The shake-reduction on the K10D will be useful as well.

For studio stuff then you might want to consider adding a cheap 50mm prime, even a manual focus one like the SMC-A 50mm F1.7, as having the ability to use very limited depth of field is often useful.

Definitely the lens - yes the K10D is better than the *istDS (I have both) but I'd much rather have the superwide than another camera body.

Both the Pentax or Sigma ultra-wide zooms would be great options, however given the Sigma is wider, at least as good optically but significantly cheaper that makes it an easy choice IMHO.

I'll be very interested to see the results and also what sort of exposure times are needed. I've dabbled a little with IR using my unmodified *istDS and the results have been pretty decent - a tripod is essential though.

Is the Tamron an adaptall one?