Digital SLRs with APS-C sized sensors currently dominates the DSLR market. The smaller sensor size translates to lower cost and compact/light weight cameras for photographers. Macro/wildlife and sports shooters love the benefits of more DOF and reach, landscape and some former 35mm film photographers hate them because their wide angle lens is no longer wide enough.
In response to the market demands, many manufacturers have produced ultra wide angle lens specially for DSLRs with APS-C sized sensors. They include the Canon EF-S 10-22mm f/3.5-4.5 USM, Nikon AF-S DX Zoom-NIKKOR 12-24mm f/4G IF-ED, Tokina AT-X 124 AF PRO DX 12-24mm f/4, Sigma 10-20mm F4-5.6 EX DC HSM, Tamron SP AF11-18mm F/4.5-5.6 Di II LD Aspherical [IF]. The first two are for Canon and Nikon photographers, respectively. The other models offer versions that are compatible with various camera manufacturers, such as Canon, Nikon, Pentax, Sony, etc.
Facing so many options, most people pay attention to build quality, chromatic aberrations, distortions, sharpness, vignetting, maximum aperture, focus speed, and cost. Unfortunately none of them seems to be perfect or excels in every aspects of the consideration. For example of the comparison, please read the excellent review at Nikonians.org (has all but the Canon ultra wide angle lenses). Most cost conscious photographers seem to narrow their choices down to the Tokina and Sigma. They are equally price at B&H. On the Internet, you can probably find equal number of people who love their Tokina or Sigma. I have found it strange that few consider the important aspect of wide angle lens: the minimum focus distance (or magnification ratio). The table below summarizes the difference.
|Lens||Minimum focus distance||Magnification ratio|
|Canon 10-22||0.24m / 9.4 in||1:6|
|Nikkor 12-24||0.30m / 11.8 in||1:8.3|
|Tokina 12-24||0.30m / 11.8 in||1:8|
|Tamron 10-18||0.25m / 9.8 in||1:8|
|Sigma 10-20||0.24m / 9.4 in||1:6.7|
John Shaw in his book Nature Photography Field Guide described one of the most effective ways of using wide angle lens is to get the lens very close to a foreground subject while keeping the horizon high in the frame in order to increase the apparent depth of the scene. This technique produces an photo that gives viewers the ability to reach out and interact with the foreground. Smaller minimum focus distance helps photographer to get a frame-filling foreground, which enhances the effectiveness of the wide angle technique. The Sigma clearly has some advantages in this aspect.It could be debatable if the difference is truly significant. It is also highly dependent on how photographers use the lens. As a matter of fact, I see more photos shot with wide angle lens pointing horizontally rather than downward as in the technique described by John Shaw. Pictures certainly are worth more than a thousand words. I hope someone who has access to both lenses run a test using this particular shooting technique to compare.