The Sigma 12-24mm f/4.5-5.6 EX DG HSM lens is a professional-level wide-angle zoom lens made by Sigma Corporation

Sigma Corporation

is a Japanese company founded in 1961, manufacturing cameras, lenses, flashes and other photographic accessories. All Sigma products are produced in the company's own Aizu factory in Bandai, Fukushima, Japan...

. It is the widest rectilinear

Rectilinear lens

In photography, a rectilinear lens is a photographic lens that yields images where straight features, such as the walls of buildings, appear with straight lines, as opposed to being curved. In other words, it is a lens with little or no barrel or pincushion distortion...

 lens available for full-frame 35mm SLR cameras, providing a field of view of 122 degrees. Other lenses available with focal lengths of 12mm or less are either incompatible with full-frame cameras or are intentionally distorted

Fisheye lens

In photography, a fisheye lens is a wide-angle lens that takes in a broad, panoramic and hemispherical image. Originally developed for use in meteorology to study cloud formation and called "whole-sky lenses", fisheye lenses quickly became popular in general photography for their unique, distorted...

. The Sigma 12-24 has low distortion even compared to less wide zooms like the Canon EF 16-35mm lens

Canon EF 16-35mm lens

The EF 16-35mm 2.8L USM lens is a professional wide-angle lens made by Canon Inc. It replaced the EF 17-35mm 2.8L USM lens, which had itself replaced the EF 20-35 2.8L lens.The lens has an EF mount to work with the EOS line of cameras...

.

This lens is available in Canon

Canon EF lens mount

Introduced in 1987, the EF lens mount is the standard lens mount on the Canon EOS family of SLR film and digital cameras. EF stands for "Electro-Focus": automatic focusing on EF lenses is handled by a dedicated electric motor built into the lens...

, Nikon

Nikon F-mount

The Nikon F-mount is a type of interchangeable lens mount developed by Nikon for its 35 mm SLR cameras. The F-mount was first introduced on the Nikon F camera in 1959, and features a three lug bayonet mount with a 44 mm throat and a flange to focal plane distance of 46.5 mm...

, and Sigma

Sigma SA mount

The Sigma SA mount is a design of lens mount designed by the Sigma Corporation of Japan for use on their single-lens reflex camera designs. The SA mount uses a bayonet mount which is physically similar to the Pentax K mount but uses a flange focal distance of 44 mm, identical to that of the Canon...

, Pentax

Pentax K mount

The Pentax K mount, sometimes referred to as the "PK mount", is a lens mount standard for mounting interchangeable photographic lenses to 35 mm single-lens reflex cameras. It was created by Pentax in 1975, and has been used by all Pentax 35 mm and digital SLRs since...

, and Sony mounts. HSM focusing is available only in the Canon, Nikon, and Sigma variants. The build quality is typical of Sigma EX lenses, with a painted metal lens barrel and damped focus and zoom rings. As expected for a lens of these specifications, there is a large protruding front element.