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 Panasonic 20mm F1.7 ASPH for their suitability to various photography scenarios:
Size and Weight Comparison
The size of a lens is an important deciding factor when comparing two lenses. Samyang 21mm F1.4 ED AS UMC CS is the longer of the two lenses at 68mm. The Panasonic 20mm F1.7 ASPH with a length of 26mm, is 42mm shorter. Besides being longer, the Samyang 21mm F1.4 ED AS UMC CS also has a larger diameter of 64mm compared to the Panasonic 20mm F1.7 ASPH's 63mm diameter.
The weight of a lens is as important as its external dimensions, especially if you are planning to hand hold your camera and lens combination for longer periods. Panasonic 20mm F1.7 ASPH weighs 100g, 63% (175g) 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 Prime Lenses in Micro Four Thirds Mount for Size Comparison
Lens Mounts
Both the Samyang 21mm F1.4 ED AS UMC CS and the Panasonic 20mm F1.7 ASPH 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-5, Panasonic GH6 and OM System OM-1.
Samyang 21mm F1.4 ED AS UMC CS is also available in Canon EF-M , Fujifilm X and Sony E mounts.
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. Panasonic 20mm F1.7 ASPH is a prime lens with fixed focal lenght of 20mm which has an effective (full-frame 35mm equivalent) focal range of 40mm when used on a FourThirds format camera.