The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 24-70mm F2.8 EX DG HSM and the Pentax 17-70mm F4.0 AL SDM 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 24-70mm F2.8 EX DG HSM is the longer of the two lenses at 95mm. The Pentax 17-70mm F4.0 AL SDM with a length of 94mm, is 1mm shorter. Besides being longer, the Sigma 24-70mm F2.8 EX DG HSM also has a larger diameter of 89mm compared to the Pentax 17-70mm F4.0 AL SDM'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. Pentax 17-70mm F4.0 AL SDM weighs 485g, 38% (305g) lighter than the Sigma 24-70mm F2.8 EX DG HSM's weight of 790g.
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 Sigma 24-70mm F2.8 EX DG HSM has a filter size of 82mm whereas the Pentax 17-70mm F4.0 AL SDM has a 67mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 82mm filters that we recommend you to consider for the Sigma 24-70mm F2.8 EX DG HSM:
And these are the 67mm filters that we recommend for the Pentax 17-70mm F4.0 AL SDM:
Lens Mounts
Both the Sigma 24-70mm F2.8 EX DG HSM and the Pentax 17-70mm F4.0 AL SDM has the same Pentax KAF3 lens mount. Some of the latest released cameras that are compatible with the Pentax KAF3 lenses are , and .
Sigma 24-70mm F2.8 EX DG HSM is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (FX) mounts.
Focal Range
Sigma 24-70mm F2.8 EX DG HSM has a focal range of 24-70mm and
2.9X zoom ratio . When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
36 - 105mm.
On the other hand, the Pentax 17-70mm F4.0 AL SDM 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.