The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Samyang 21mm F1.4 ED AS UMC CS and the Sigma 19mm F2.8 DN for their suitability to various photography scenarios:
Size and Weight Comparison
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. Sigma 19mm F2.8 DN weighs 140g, 49% (135g) lighter than the Samyang 21mm F1.4 ED AS UMC CS's weight of 275g.
Below you can find the dimension and weight table of the Wideangle Prime Lenses in Micro Four Thirds Mount for size comparison purposes.
Wideangle Lenses in Micro Four Thirds Mount for Size Comparison
Lens Mounts
Both the Samyang 21mm F1.4 ED AS UMC CS and the Sigma 19mm F2.8 DN has the same Micro Four Thirds lens mount. Some of the latest released cameras that are compatible with the Micro Four Thirds lenses are OM System OM-1 II, Panasonic G9 II and OM System OM-5.
Samyang 21mm F1.4 ED AS UMC CS is also available in Canon EF-M , Fujifilm X and Sony E mounts.
Sigma 19mm F2.8 DN is also available in Sony E mount.
Focal Range
Samyang 21mm F1.4 ED AS UMC CS is a prime lens with fixed focal lenght of 21mm which has an effective (full-frame 35mm equivalent) focal range of
42mm when used on a APS-C / DX format camera.
On the other hand, the Sigma 19mm F2.8 DN is a prime lens with fixed focal lenght of 19mm which has an effective (full-frame 35mm equivalent) focal range of 28.5mm when used on a APS-C / DX format camera.