The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Sigma 30mm F1.4 EX DC HSM and the Pentax 21mm F3.2 AL L 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 30mm F1.4 EX DC HSM is the longer of the two lenses at 59mm. The Pentax 21mm F3.2 AL L with a length of 25mm, is 34mm shorter. Besides being longer, the Sigma 30mm F1.4 EX DC HSM also has a larger diameter of 77mm compared to the Pentax 21mm F3.2 AL L's 63mm 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 21mm F3.2 AL L weighs 140g, 67% (290g) lighter than the Sigma 30mm F1.4 EX DC HSM's weight of 430g.
Filter Threads
The Sigma 30mm F1.4 EX DC HSM has a filter size of 62mm whereas the Pentax 21mm F3.2 AL L has a 49mm diameter. Larger filters are generally more expensive than the smaller ones given all the other features are equal.
Below are links to the 62mm filters that we recommend you to consider for the Sigma 30mm F1.4 EX DC HSM:
And these are the 49mm filters that we recommend for the Pentax 21mm F3.2 AL L:
Lens Mounts
The Sigma 30mm F1.4 EX DC HSM has the Sigma SA lens mount whereas the Pentax 21mm F3.2 AL L has the Pentax KAF lens mount. Some of the latest released cameras that are compatible with these mounts are Sigma SD1 Merrill, Sigma SD1 and for the Sigma SA Mount and Pentax K-3 III Mono, Pentax KF and Pentax K-3 III for the Pentax KAF Mount.
Sigma 30mm F1.4 EX DC HSM is also available in the Canon EF-S , Nikon F (DX), Four Thirds, Pentax KAF and Sony Alpha mounts.
Pentax 21mm F3.2 AL L is also available in Pentax KAF mount.
Focal Range
Sigma 30mm F1.4 EX DC HSM is a prime lens with fixed focal lenght of 30mm which has an effective (full-frame 35mm equivalent) focal range of
45mm when used on a APS-C / DX format camera.
On the other hand, the Pentax 21mm F3.2 AL L is a prime lens with fixed focal lenght of 21mm which has an effective (full-frame 35mm equivalent) focal range of 31.5mm when used on a APS-C / DX format camera.
