The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 50mm F1.4 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. Pentax 17-70mm F4.0 AL SDM is the longer of the two lenses at 94mm. The Sigma 50mm F1.4 EX DG HSM with a length of 68mm, is 26mm shorter. On the other hand, the Sigma 50mm F1.4 EX DG HSM has a larger diameter of 85mm 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, 3% (20g) lighter than the Sigma 50mm F1.4 EX DG HSM's weight of 505g.
Filter Threads
The Sigma 50mm F1.4 EX DG HSM has a filter size of 77mm 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 77mm filters that we recommend you to consider for the Sigma 50mm F1.4 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 50mm F1.4 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 50mm F1.4 EX DG HSM is also available in the Canon EF , Sony Alpha, Sigma SA, Nikon F (FX) and Four Thirds mounts.
Focal Range
Sigma 50mm F1.4 EX DG HSM is a prime lens with fixed focal lenght of 50mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
75mm.
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.
