Tischer's Review of the Sigma 12-24mm F4.5-5.6 DG HSM
The folllowing pictures were taken with a Canon 1D Mark II which has a crop factor of 1.25, resulting in a 15mm equivalent lens. Note this lens can also be used as a full frame 12mm, but this is beyond the scope of this review.
There were several flare spots which were removed in photoshop due to the bright windows. Purple fringing on the window frames was also removed. The purple fringing was very mild, here is a link to the uncorrected photo which has only been resized.
Taken on a Canon digital Rebel (300d)with Sigma 12-24mm at 12mm, F11, 1/200", ISO 100
This is one huge depth of feild, everything from 5" to infinity is in focus.
Looking at the original file shows
there is no CA or PF anywhere, even where the black edge of the building meets the white clouds in the corner of the frame. That is a real torture test for for any wide angle lens, and the Sigma performs very well. I don't think the Canon 10-22mm could pull this off without green/red Chromatic Aberration. Sharpness is excellent from corner to corner.
This may be somewhat of an unfair shot because the highlights are blown in the sky. Still, I think it represents an everyday real world picture. The silouette of the tree branches against the overexposed sky at the top right of the frame cause a purple halo (purple fringing) around the tree branches. This purple band is about 5-7 pixels wide. There is a slight loss of sharpeness due to the lens being wide open, you should also account for the shallow depth of feild since this shot was taken at f/4.5
Taken on a Canon digital Rebel (300d) with Sigma 12-24mm, 12mm, F4.5, 1/60", ISO 100, flash bounced off ceiling
With such a wide perspective, you can get the smallest details to fill a large portion of the frame. For example the lamp in the photo is actually the same size as my friends head. The lamp appears huge because it is closer to the corner of the frame (and closer to the lens). Try to keep your friends nose in the center of the frame so it does not also look huge.
Taken on a Canon digital Rebel (300d) with Sigma 12-24mm, 12mm, F4.5, 1/50", ISO 800
Super wide persepctive. At first glance it looks like the picture encorperates floor to ceiling. This lens is great for urban photography where you can't always move further away from your subject. This also helps keep people out of your scene since you don't need to stand as far back from your subject. Again, this picture was taken with a 1.6 crop factor camera resulting in an equivalent 19mm perspective, just imagine on a normal camera shooting at 12mm!
Seeing the huge bulging crystal ball of a front element on this lens was the main deterent from me purchasing this lens. Based on looks alone I thought for sure this lens would have major CA, as you can see it's no where close to being as bad as the Canon Kit lens.
Purple Fringing comparison between the Sigma 12-24mm and the Canon 18-55mm EFS
I should also note the build quality is excellent. Focusing is fast and whisper quiet. The focus ring does not rotate during auto focusing, and the user has full time manual focus. The DOF is so wide you almost don't need to focus. My only complaint is the zoom ring is really stiff, it causes the lens to rotate on the camera mount because there is enough play in the lens locking pin. Perhaps this will wear in, but I haven't seen any improvement in the last month. Since the petal hood is part of the lens, a special removable hoop comes with the lens to allow a lens cap to be fitted. My hoop fits rather loose but it has never fallen off. Anybody wanting to use a threaded filter is most likely screwed, an 82mm filter can be threaded to the lens cap hoop but the hoop alone will cause vignetting at 12mm.
Ive noticed problems when using the Sigma 12-24mm on a digital rebel with 420ex flash. I had only the center focus sensor active in the shots below. Covering the focus light on the 420ex does not seem to have any effect. After taking about 100 pictures of various test patterns, its obvious this lens always back focuses when my 420ex flash is used.
Apparently when the AF assist beam is used, the lens front focuses several centimeters. In the video I state the lens front focuses 10mm off, I should have said 10 cm off. The flash exposure also appears to be off, but this could be a variation in using an external vs internal flash.