The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 8-16mm F4.5-5.6 DC HSM and the Pentax 21mm F3.2 AL L for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is a crucial factor to consider when comparing two lenses. Sigma 8-16mm F4.5-5.6 DC HSM is the longer of the two lenses at 106mm. The Pentax 21mm F3.2 AL L with a length of 25mm, is 81mm shorter. Besides being longer, the Sigma 8-16mm F4.5-5.6 DC HSM also has a larger diameter of 75mm compared to the Pentax 21mm F3.2 AL L's 63mm diameter.
The weight of a lens is equally significant as its external dimensions, particularly if you intend to handhold your camera and lens combination for extended periods. Pentax 21mm F3.2 AL L weighs 134g, 75% (421g) lighter than the Sigma 8-16mm F4.5-5.6 DC HSM's weight of 555g.
Lens Mounts
The Sigma 8-16mm F4.5-5.6 DC HSM has the Pentax KAF3 lens mount whereas the Pentax 21mm F3.2 AL L has the Pentax KAF lens mount. Some of the latest released cameras that are compatible with these mounts are , and for the Pentax KAF3 Mount and Pentax K-3 III Mono, Pentax KF and Pentax K-3 III for the Pentax KAF Mount.
Sigma 8-16mm F4.5-5.6 DC HSM is also available in the Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Pentax 21mm F3.2 AL L is also available in Pentax KAF mount.
Focal Range
Sigma 8-16mm F4.5-5.6 DC HSM has a focal range of 8-16mm and
2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
12-24mm when used on a APS-C / DX format camera.
On the other hand, the Pentax 21mm F3.2 AL L is a prime lens with fixed focal lenght of 21mm which has an effective (full-frame 35mm equivalent) focal range of 31.5mm when used on a APS-C / DX format camera.
