The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-DA 11-18mm F2.8 and the Sigma 8-16mm F4.5-5.6 DC HSM 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 HD Pentax-DA 11-18mm F2.8 with a length of 100mm, is 6mm shorter. On the other hand, the HD Pentax-DA 11-18mm F2.8 has a larger diameter of 90mm compared to the Sigma 8-16mm F4.5-5.6 DC HSM's 75mm 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. Sigma 8-16mm F4.5-5.6 DC HSM weighs 555g, 21% (149g) lighter than the HD Pentax-DA 11-18mm F2.8's weight of 704g.
Below you can find the dimension and weight table of the Wideangle Zoom Lenses in Pentax KAF3 Mount for size comparison purposes.
Ultra-Wideangle Lenses in Pentax KAF3 Mount for Size Comparison
Lens Mounts
Both the HD Pentax-DA 11-18mm F2.8 and the Sigma 8-16mm F4.5-5.6 DC HSM has the same Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with the Pentax KAF3 lenses are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III.
Sigma 8-16mm F4.5-5.6 DC HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
HD Pentax-DA 11-18mm F2.8 has a focal range of 11-18mm and
1.6X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
16.5-27mm when used on a APS-C / DX format camera.
On the other hand, the 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.