Sigma 20-40mm F2.8 EX Aspherical DG DF AutoFocus Wide Angle Zoom Lens           

This 20-40mm f2.8 EX Aspherical DG DF lens provides f2.8 large maximum aperture for all focal lengths between ultra-wide angle 20mm to 40mm. The lens has minimum focus distance of 11.8 inches (30cm) at all focal lengths and maximum magnification is 1: 4.6. It incorporates aspherical lenses in the front lens group and rear lens group to minimize distortion, astigmatism and spherical aberration.

The lens is equipped with a DF (Dual Focus) mechanism and also an IF (Inner Focus) system. It is easy to hold the lens during shooting, since the focusing ring does not rotate during auto focusing, and yet it provides adequate dampening of the focusing ring during manual focusing of the lens. This lens is designed to be desirable for both digital SLR cameras and conventional 35mm SLR camera.

Sigma's 20-40mm f2.8 EX Aspherical DG DF lens is equipped with a removable type lens hood (Petal shaped hood) to prevent extraneous light harmful for image quality.
Construction 13 groups /17 elements
Angle of view 94.5°-56.8°
F stop range 32
Closest Focusing Distance 30cm / 11.8"
Maximum Magnification 1:4.6
Filter Size 82mm
Dimensions (Length x Diameter) 89 x 107.8mm / 3.5 x 4.2"
Full Extended Length 119 mm/ 4.7 "
Weight 595g / 20.9oz.
For Canon
 For Nikon