The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 17-70mm F2.8-4 DC OS HSM C 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. Pentax 17-70mm F4.0 AL SDM is the longer of the two lenses at 94mm. The Sigma 17-70mm F2.8-4 DC OS HSM C with a length of 82mm, is 12mm shorter. On the other hand, the Sigma 17-70mm F2.8-4 DC OS HSM C has a larger diameter of 79mm 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. Sigma 17-70mm F2.8-4 DC OS HSM C weighs 465g, which means it is 20g (4%) lighter than the Pentax 17-70mm F4.0 AL SDM which has a weight of 485g.
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 17-70mm F2.8-4 DC OS HSM C has a filter size of 72mm 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 72mm filters that we recommend you to consider for the Sigma 17-70mm F2.8-4 DC OS HSM C:
And these are the 67mm filters that we recommend for the Pentax 17-70mm F4.0 AL SDM:
Lens Mounts
Both the Sigma 17-70mm F2.8-4 DC OS HSM C 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 17-70mm F2.8-4 DC OS HSM C is also available in Canon EF , Sony Alpha, Sigma SA and Nikon F (DX) mounts.
Focal Range
Both lenses have the same focal range of
17-70mm but while Sigma 17-70mm F2.8-4 DC OS HSM C has the fastest aperture of
F2.8 - F4.0, the Pentax 17-70mm F4.0 AL SDM's widest aperture value is
F4.0.