The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 10-20mm F4-5.6 EX DC HSM and the HD Pentax-DA 11-18mm F2.8 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 F4-5.6 EX DC HSM with a length of 81mm, is 19mm 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 F4-5.6 EX DC HSM's 84mm 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 F4-5.6 EX DC HSM weighs 470g, which means it is 234g (33%) lighter than the HD Pentax-DA 11-18mm F2.8 which has a weight of 704g.
Filter Threads
The Sigma 10-20mm F4-5.6 EX DC HSM has a filter size of 77mm whereas the HD Pentax-DA 11-18mm F2.8 has a 82mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 77mm filters that we recommend you to consider for the Sigma 10-20mm F4-5.6 EX DC HSM:
And these are the 82mm filters that we recommend for the HD Pentax-DA 11-18mm F2.8:
Lens Mounts
The Sigma 10-20mm F4-5.6 EX DC HSM has the Pentax KAF lens mount whereas the HD Pentax-DA 11-18mm F2.8 has the Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with these mounts are Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III for the Pentax KAF Mount and Pentax K-3 III Monochrome, Pentax KF and Pentax K-3 III for the Pentax KAF3 Mount.
Sigma 10-20mm F4-5.6 EX DC HSM is also available in Canon EF , Four Thirds, Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 10-20mm F4-5.6 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.
On the other hand, the 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.