Why I use a “cheap” lens.
Quite a few people have written to me and asked; “why do you recommend and use the Sigma 10-20mm F/4-5.6 lens; it’s cheap, and not the sharpest lens, even according to your own reviews.” The answer is always the same; it does the job. In all the years I’ve used this lens, no client has ever complained to me about lack of resolution. They might complain about my prices and job completion time, but never resolution. When I submit photos to magazine editors, they never complain about resolution either. I’ve actually cropped an image in half to make a horizontal shot into a vertical for a cover photo with the 12mp A700, it turned out plenty sharp and looked great! As long as you make sure the lens is focused properly, and stop it down a little, everything will be great.
Amateurs always think sharpness is the most important thing in a picture, but it’s really the least important. If you have the sharpest lens, and slightly mis-focus, the shot is probably ruined. If your composition is poor, the shot is poor. If your light is bad, the shot is bad. When you’re photographing something for a client, you don’t want to worry about a lens that has a “wandering” focus setting, like the Tokina 11-16mm, (by “wandering” I mean the lens needs to be focused differently when changing focal lengths at less than infinity focusing distances; and has nothing to do with the AF problem on my review copy). The Tokina is much sharper at wider focal lengths than the Sigma, but the focusing issue is the biggest reason I wouldn’t use it indoors, or recommend it for interior/Real estate work. The Sigma 10-20mm F/4-5.6 is very stable when focused at the infinity mark for any subject matter past 15′ (5m) at all focal lengths, and that allows me to “focus and forget.” Is that the absolute sharpest focusing point for all zoom lengths? probably not, but who cares, it’s sharp enough to make my clients happy, and doing that helps free up time so I can concentrate on composition and lighting, which is far more important in making a great picture.
When I have a tough lighting job ahead of me, I always pull out the Sigma and Sony A580, and keep the Sony A900 and CZ 16-35mm for back-up. The CZ 16-35mm focuses similarly to the Tokina, and doesn’t have the great ghosting control of the Sigma. Sure, the CZ 16-35mm is sharp, but I don’t really need the resolution.
So the bottom line is; I use tools that I trust, and can count on to make me and others happy. The Sigma is cheap, but It handles ghosting very well, distortion is very low and manageable past 12mm, and is sharp stopped down a little at longer focal lengths, which I use most often. My average image specs for this lens are around 13-16mm at F/7.1, ISO 200.
As I said in the review, if I didn’t already have the Sigma 10-20mm F/4-5.6, I’d probably go with the new Sigma 10-20mm F/3.5, it has the same basic characteristics as the older Sigma, but is a little faster with better distortion control at the short end. It does cost more than the old Sigma, but I would pay the extra amount.