which 10-20 - if at all?

I have the Sigma 10-20mm and Love it. Not that I use it that often (I find the 16-45 more suitable for most situations). However when needed it comes into its own. As for QC issues with this lens, the only mounts I have heard problems with are Canon. Any other mounts, none at all.
This was taken on Sunday with the Sigma....

I can't agree with this, Steve! There are noticeable differences between the quality of images that lenses will produce and this will impact in the real world on what a photographer can achieve.

In the case of the lenses under discussion here, I haven't had the chance to use both, so it is hard to say whether or not the difference will be so apparent. Given the quality of the results the 12-24 (which I have) produces (and comparing it to other zooms), I would guess that there would be a real difference between that and the Sigma - probably in terms of resolution (the 12-24 is a remarkably sharp lens) and distortion (it has the least distortion of any wide angle I have used). However, I can't say that with any certainty because I haven't used the Sigma, and I have certainly seen that this lens can also produce excellent images such as the one above (though - to take another example - so can the DA18-55, but give me the DA17-70 any day).

The other argument for the 12-24 is that it's a more practical range - necessitating fewer lens changes. 4mm at the wide end is a lot. And I've found that 24mm often comes in handy (and with the 12-24's excellent resolution you can also crop quite severely before serious image degradation sets in). I often use just the 12-24 when wandering around historical sites, towns (taking shots of people, buildings, context shots etc.), and I reckon that I'd find 10-20mm a lot less practical - though, to be fair, the extra 2mm wide would occasionally be nice.

Still, having said all that, if I was getting a new ultra-wide now I'd almost certainly opt for a Sigma (though a second hand DA or Samsung would be tempting). The current pricing of the 12-24 - given that it's a consumer grade zoom (allbeit optically excellent) - is ridiculous. I was lucky enough to get one before the recent rises and with £50 off.

I am curious about the Sigma though. I wish someone would do a direct comparison which could put this debate to bed - the 12-24 vs. 10-20 dispute seems to be never ending with both sides convinced of 'their' lens's merits!

I'd like to put a vote in for the Tamron 10-24. I got one at Christmas and did a bit of reading up beforehand and am very pleased with it.

What I found what that while the Pentax/Samsung 12-24 is undoubtedly a better performing lens, the Sigma 10-20 and Tamron are both pretty good and both have good reviews and very satisfied users. For me, the Tamron was much better value and the 24mm reach is useful, as I can use it as a walkaround lens (albeit a wide one).

I'm very happy with the performance; I think that it depends what you want it for. If it is to see how you get on with an ultrawide and if it suits your style, I'd recommend the Tamron or Sigma. If you get on well with it and are unhappy with the qualiy, both seem to hold their value well, so you could sell it and buy the Pentax 12-24. Whereas if you're in to pixel peeping and want the technically 'best' lens, the Pentax is probably the one to get.

From my experience, the limiting factor is my technique at such wide angles, not the lens!

I love my Sigma 10/20.....I have a "Good one!"......,sharp to the edges!

Anyone else noticed that the price on the "old" Sigma 10/20 (f4-5.6) seems to be going up, but the "new" Sigma (f3.5) is coming down - there's barely £50 in it now.

Is this a result of the universal slateing the f3.5 version has been getting in reviews so noone is buying it...? Second-hand prices seem to be staying-up, although maybe when the 8-16mm comes out later in the year there will be more?

Well my Sigma 10-20 has just bought me a new netbook so I a happy. The netbook will get far more use than the lens ever did .

Of the two Sigmas, the cheaper variable aperture one is actually sharper. Neither is as sharp as the 12-24, but then nor should they be for about a third of the price.

I might agree with that analogy, there are many forums for performance cars & bikes where such a decision is equally agonised over.

The tyres on a car are probably the most important part as they do all the work (exactly the same as a lens on a camera) - You can sacrifice performance for economy, but you can rarely get both.

Hmmm, and just to throw a spanner in the works...just as I was settling-on the Sigma 10-20 (old version) for my Wide-Angle urges, I found the Pentax DA 12-24mm for just (ha ha) £529 ...! (please don't say "I got one for £300 last year" etc, that's no help to me...).

Now if only it was F2... I really want something fast AND wide, for work shots, but don't want to be tied to a Prime... (Plenty of affordable options at the 17-50 range fortunetly!)

p.s.
Yes I know I'm already talking about spending more on lens than on body. If I had a choice...

That's pretty good... funny that the price is higher than the RRP quoted! Cheapest I could find was £576 link

The thing is fast and ultra-wide don't really go together. The only fast wide lens I can think of is the DA14 f2.8 and that has the bulk of the 12-24 with no better image quality (I think) and without the extra 2mm wide & 9mm long. You only start getting faster at 16mm up.

On the other hand, even with just f4 I've noticed my 12-24 is a very good performer in low light. This is partly to do with the detail that it captures. But also, I think, any wide lens is going to perform better in low light due to the amount of light it is letting in (correct me if I'm wrong - I've a feeling I might be).

BTW - £529, if you can get it for that, is an exceptional price for a new DA12-24 - in fact, I'd say that was a good s/h price these days.

Arrival at that realisation does not take long! It's mainly about the glass, so you may spend more time making decisions about it, than on bodies.

More than that, I'd say it either has to be a grey import or their website is displaying out of date/out of stock items. Someone go try and buy one and let us know

Where can you get one for £50 - I'll take one for that!?

Tim, they are definately not grey-imports. Walters have a few branches all in my area & are a Pentax Pro dealer (which means 24 month warrantee I believe). As for stock/price errors, I cannot comment.