I picked up the Sigma 10-20 yesterday
I haven't done exhaustive comparisons with my other lenses yet, but initial tests seem to show the copy I have to be nice and sharp (all things considered). At the tele-end in the 17-20mm range where it overlaps with my Canon 17-85mm IS lens, the Sigma 10-20 is significantly sharper, especially at the edges. It also has MUCH better CA than the 17-85 (which is pretty bad in the corners at the wide end).
Its not perfect by any means, but I'm certainly happier with its overall image quality than I was when I got my 17-85 IS (which is still a good step up from the kit lens as far as image quality).
It might not be a fair test comparing one lens at its "tele" end of the zoom with another at its "wide" end... but its the best I can do. And I must say that whenever I need to take shots in the future where either lens will do... I will be reaching for the Sigma - no question (unless I need to use the IS).
At the 10mm end of the Sigma's range though... whoah.. its quite a different view of the world. I wasn't ready for just how exaggerated the perspective is, especially in the corners. There seems to be quite a skill in simply getting some 10mm shots to look "natural"... as things tend to get stretched out towards the corners as you approach them, and you don't want to put people or strong verticals near the corners unless you are wanting that effect. Of course PS2 has perspective effects to correct a lot of this if you want to, but ideally you shouldn't have to. Apart from this massive perspective effect (which I assume isn't a "fault" of the lens, it is simply a necessity when you're trying to squeeze over 100deg of view onto the sensor without being a fish-eye) there is suprisingly very little distortion and good decent flare control. I should point out though that the corners *are* a bit softer at 10mm than at 17-20mm, especially so at wide apertures... but they were better than I was expecting and certainly well within my acceptable limits.
I think it will take some time to really get the most out of 10-12mm beyond novelty shots, but I've seen enough today to know it will be a very useful little weapon to have in the arsenal. Things start to look normal again around 14-15mm, and by 20mm it is just a lovely sharp regular wide-angle lens.
So here are some shots from today:
1. Obligatory wide-angle novelty shot. My cats will hate me for turning them into big-headed monsters!
2. Indiana Tea House, Cottesloe. This is a 10mm shot where I was trying *not* to eggagerate the perspective effect... yet it is still quite noticable (but quite acceptable IMHO). Also note that there is no vignetting when I use a normal-size (ie not slim-line) polariser! yaay!
3. This 10mm shot was the worst shot of the day with regards to flare... and although the flare is quite obvious, it is much better than the likes of the kit lens. Little patches of flare don't worry me too much, its the large "veil" flare that seems to wash out 1/2 an image that I really hate, and this seems to be pretty good in that regard. Also note that the flare seemed to be the worst when the sun was just on the edge of the image... it was actually better when the sun was in the picture (or obviously when the sun was way out of the image and being blocked by the lens hood).
4. This is a shot at 20mm... which looks lovely and sharp in high-res.. I think it will be a great landscape lens in the 15-20mm range.
5. Canning River - Applecross. Its great for shooting things that are flat horizontal on the ground, as it can cover a large area and makes the camera appear directly above the scene... but I had to be careful not to include my feet in the image!
6. Canning River - Applecross. These are the kinds of scenes I really bought this lens for... where I can use that unique perspective to add drama and effect and depth to the geometry in the scene and really emphasize a particular idea. I think this particular shot is missing something, but it gives me a glimpse at the possibilities I think.
7. Although this shot doesn't really say much about the lens, I took it with the lens last night at a friend's house (1/8th second hand held @10mm) and I thought it was worth posting for a laugh
I hope that can help... I might be able to do some "proper" comparison shots on the weekend and post some 100% crops for the pixel peepers out there... but my gut feeling about the lens is a very good one....
As you say Zig.. perhaps you got one of the early "dud" ones?