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 DA 20-40mm F2.8-4 ED DC 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. Pentax DA 20-40mm F2.8-4 ED DC WR is the longer of the two lenses at 69mm. The Sigma 50mm F1.4 EX DG HSM with a length of 68mm, is 1mm shorter. On the other hand, the Sigma 50mm F1.4 EX DG HSM has a larger diameter of 85mm compared to the Pentax DA 20-40mm F2.8-4 ED DC WR's 71mm 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 DA 20-40mm F2.8-4 ED DC WR weighs 283g, 43% (222g) 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 DA 20-40mm F2.8-4 ED DC WR has a 55mm 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 55mm filters that we recommend for the Pentax DA 20-40mm F2.8-4 ED DC WR:
Lens Mounts
Both the Sigma 50mm F1.4 EX DG HSM and the Pentax DA 20-40mm F2.8-4 ED DC WR 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 DA 20-40mm F2.8-4 ED DC WR has a focal range of 20-40mm and 2.0X zoom ratio which has an effective (full-frame 35mm equivalent) focal range of 30-60mm when used on a APS-C / DX format camera.
