The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 18-35mm F1.8 DC HSM and the PENTAX15-30mm F2.8 ED WR 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. PENTAX15-30mm F2.8 ED WR is the longer of the two lenses at 144mm. The Sigma 18-35mm F1.8 DC HSM with a length of 121mm, is 23mm shorter. Besides being longer, the PENTAX15-30mm F2.8 ED WR also has a larger diameter of 99mm compared to the Sigma 18-35mm F1.8 DC HSM's 78mm 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 18-35mm F1.8 DC HSM weighs 810g, which means it is 230g (22%) lighter than the PENTAX15-30mm F2.8 ED WR which has a weight of 1040g.
Lens Mounts
The Sigma 18-35mm F1.8 DC HSM has the Pentax KAF lens mount whereas the PENTAX15-30mm F2.8 ED WR 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 18-35mm F1.8 DC HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Sigma 18-35mm F1.8 DC HSM has a focal range of 18-35mm and
1.9X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of
27-52.5mm when used on a APS-C / DX format camera.
On the other hand, the PENTAX15-30mm F2.8 ED WR has a focal range of 15-30mm and 2.0X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 22.5 - 45mm.