The type of photography that you are planning to use is an important decision factor. Here we have evaluated the PENTAX28-105mm F3.5-5.6 WR and the Sigma 17-70mm F2.8-4 DC OS 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 17-70mm F2.8-4 DC OS HSM is the longer of the two lenses at 89mm. The PENTAX28-105mm F3.5-5.6 WR with a length of 87mm, is 2mm shorter. Besides being longer, the Sigma 17-70mm F2.8-4 DC OS HSM also has a larger diameter of 79mm compared to the PENTAX28-105mm F3.5-5.6 WR's 73mm 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. PENTAX28-105mm F3.5-5.6 WR weighs 440g, which means it is 80g (15%) lighter than the Sigma 17-70mm F2.8-4 DC OS HSM which has a weight of 520g.
Below you can find the dimension and weight table of the Standard Zoom Lenses in Pentax KAF3 Mount for size comparison purposes.
Standard Lenses in Pentax KAF3 Mount for Size Comparison
Filter Threads
The PENTAX28-105mm F3.5-5.6 WR has a filter size of 62mm whereas the Sigma 17-70mm F2.8-4 DC OS HSM has a 72mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the PENTAX28-105mm F3.5-5.6 WR:
And these are the 72mm filters that we recommend for the Sigma 17-70mm F2.8-4 DC OS HSM:
Lens Mounts
Both the PENTAX28-105mm F3.5-5.6 WR and the Sigma 17-70mm F2.8-4 DC OS 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 Mono, Pentax KF and Pentax K-3 III.
Sigma 17-70mm F2.8-4 DC OS HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
PENTAX28-105mm F3.5-5.6 WR has a focal range of 28-105mm and
3.8X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
42 - 157.5mm.
On the other hand, the Sigma 17-70mm F2.8-4 DC OS HSM has a focal range of 17-70mm and 4.1X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 25.5-105mm when used on a APS-C / DX format camera.
