The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Leica SL 21mm F2 ASPH and the Sigma 28mm F1.4 DG HSM A 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 28mm F1.4 DG HSM A is the longer of the two lenses at 108mm. The Leica SL 21mm F2 ASPH with a length of 102mm, is 6mm shorter. Besides being longer, the Sigma 28mm F1.4 DG HSM A also has a larger diameter of 83mm compared to the Leica SL 21mm F2 ASPH's 73mm 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. Leica SL 21mm F2 ASPH weighs 789g, which means it is 171g (17%) lighter than the Sigma 28mm F1.4 DG HSM A which has a weight of 960g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Leica L Mount for size comparison purposes.
Wideangle Lenses in Leica L Mount for Size Comparison
The Leica SL 21mm F2 ASPH has a filter size of 67mm whereas the Sigma 28mm F1.4 DG HSM A 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 67mm filters that we recommend you to consider for the Leica SL 21mm F2 ASPH:
And these are the 77mm filters that we recommend for the Sigma 28mm F1.4 DG HSM A:
Both the Leica SL 21mm F2 ASPH and the Sigma 28mm F1.4 DG HSM A has the same Leica L lens mount. Some of the latest released cameras that are compatible with the Leica L lenses are Panasonic S5 II, Panasonic S5 II X and Sigma fp L.
Sigma 28mm F1.4 DG HSM A is also available in Canon EF , Nikon F (FX), Sigma SA and Sony E mounts.
Leica SL 21mm F2 ASPH is a prime lens with fixed focal lenght of 21mm. When it is mounted on an APS-C sensor camera with 1.5x crop, it provides a 35mm (FF) equivalent of 31.5mm
On the other hand, the Sigma 28mm F1.4 DG HSM A is a prime lens with fixed focal lenght of 28mm.