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 10-20mm F3.5 EX 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. HD Pentax-DA 11-18mm F2.8 is the longer of the two lenses at 100mm. The Sigma 10-20mm F3.5 EX DC HSM with a length of 88mm, is 12mm shorter. Besides being longer, the HD Pentax-DA 11-18mm F2.8 also has a larger diameter of 90mm compared to the Sigma 10-20mm F3.5 EX DC HSM's 87mm 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 10-20mm F3.5 EX DC HSM weighs 520g, 26% (184g) 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
Filter Threads
Both the HD Pentax-DA 11-18mm F2.8 and the Sigma 10-20mm F3.5 EX DC HSM have the same Filter thread size of 82mm.
Below are links to the 82mm filters that we recommend you to consider for these lenses:
Lens Mounts
Both the HD Pentax-DA 11-18mm F2.8 and the Sigma 10-20mm F3.5 EX 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 10-20mm F3.5 EX 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 10-20mm F3.5 EX DC HSM has a focal range of 10-20mm and 2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 15-30mm when used on a APS-C / DX format camera.