Sigma 10-20mm F4 - 5.6 EX HSM DC Zoom lens
The lens has 14 elements in 10 groups and includes 3 SLD glasses and 3 aspherical elements (one molded and two hybrid-type) that offer an excellent distortion correction as well as all aberration types.
This Sigma is equipped with a internal focus system, enhanced with the HSM system, what provides a very quick and silent autofocus, and the same way allows a full time manual override. It has a 6 blade aperture mechanism and it weighs about 470 grams.
It has a minimum focus distance of 24cm in all the range and the covering angle varies from 102,4º (10mm) to 63,8 (20mm), and it is the bigger aperture angle zoom in this sector. The Canon EF-S 10-22 has a maximum angle of 97º and Nikon 12-24 AFS DX has 99º (in spite of being a 12mm).
The front element non rotative allows the use of polarizer filters without problems, as well as a petal-type hood. It hardly changes size when using the zoom.
The distortion at 10mm is, surprisingly, almost nonexistent, allowing to photograph landscapes with almost right horizons, anyway, if we maintain the wide-angle photography doctrine inside its parameters. Starting at 14mm the lens shows pincushion distortion and it is more or less as its partners.
The vignetting is the typical for this type of zooms and it is about around 1 EV in the worst cases, that is to say, at 10mm and f4, something that you can solve if we have Photoshop CS2, using: filter / distortion / lens correction, and we can fix vignetting easily.
The lens resolution can be considered as good to very good in almost all the situations. In general lines, the resolution in the center is excellent and stays as good in the corners, improving enough at medium aperture settings.