The ultra-wide angle Sigma 10-20, with is zoom aspect, covers a huge wide angle range from 15mm to 30mm. Also, with a minimum focus length of 30cm (or 11.8 inches), this lens is absolutely perfectly suited to digital SLR cameras.
By incorporating, within the front lens group, a hybrid aspherical lens the Sigma 10-20 effortlessly minimises ugly distortion and astigmatism and the molded glass aspherical lens in the rear lens group works to perfectly limit spherical aberration. Distortion is always a big issue, so finding a lens like the Sigma 10-20 that can eliminate it so easily and effectively is a big deal, providing wonderful image quality each and every time.
The Sigma 10-20 is also a wonderful lens when it comes to the mechanics of its zoom function. The lens has an internal focusing system, thus eliminating the likelihood of any front lens rotation, which would potential affect the hybrid aspherical lens and therefore the distortion control. There are a number of features which also make this lens much easier to hold and use whilst focusing. Firstly, the lens itself does not change length at all whilst focusing, unlike some of its contemporaries. Also, when using the auto focus, the lens does not rotate, which has caused a few surprises in the past with other lenses I have used. Finally, it should also be noted that the Sigma 10-20 utilises a Dual Focus mechanism.
The maximum aperture on the Sigma 10-20 is f/4 to f/5.6 and the minimum is f/22. The lens construction comprises 14 elements in 10 groups and sports a six blade diaphragm. At 17.5 ounces is it also very light weight and it is also nice and compact, making it easy and convenient to transport. The Sigma 10-20 is a truly wonderful ultra wide angle lens and I have used it to take some of the best photographs of my career; it is definitely worth every penny of its extremely reasonable list price.