The type of photography that you are planning to use is an important decision factor. Here we have evaluated the HD Pentax-FA 31mm F1.8 Ltd and the Sigma 24mm F1.8 EX DG 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 24mm F1.8 EX DG is the longer of the two lenses at 83mm. The HD Pentax-FA 31mm F1.8 Ltd with a length of 69mm, is 14mm shorter. Besides being longer, the Sigma 24mm F1.8 EX DG also has a larger diameter of 84mm compared to the HD Pentax-FA 31mm F1.8 Ltd's 65mm 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. HD Pentax-FA 31mm F1.8 Ltd weighs 341g, which means it is 159g (31%) lighter than the Sigma 24mm F1.8 EX DG which has a weight of 500g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Pentax KAF Mount for size comparison purposes.
Wideangle Lenses in Pentax KAF Mount for Size Comparison
Filter Threads
The HD Pentax-FA 31mm F1.8 Ltd has a filter size of 58mm whereas the Sigma 24mm F1.8 EX DG has a 77mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 58mm filters that we recommend you to consider for the HD Pentax-FA 31mm F1.8 Ltd:
And these are the 77mm filters that we recommend for the Sigma 24mm F1.8 EX DG:
Lens Mounts
Both the HD Pentax-FA 31mm F1.8 Ltd and the Sigma 24mm F1.8 EX DG has the same Pentax KAF lens mount. Some of the latest released cameras that are compatible with the Pentax KAF lenses are Pentax K-3 III Mono, Pentax KF and Pentax K-3 III.
Sigma 24mm F1.8 EX DG is also available in Canon EF , Nikon F (FX), Four Thirds, Pentax KAF, Sony Alpha, Sigma SA, Canon EF, Sony Alpha, Sigma SA and Nikon F (FX) mounts.
Focal Range
HD Pentax-FA 31mm F1.8 Ltd is a prime lens with fixed focal lenght of 31mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of
46.5mm.
On the other hand, the Sigma 24mm F1.8 EX DG is a prime lens with fixed focal lenght of 28mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 42mm.
