Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Panasonic 25mm F1.4 II ASPH is the longer of the two lenses at 55mm. The Panasonic 20mm F1.7 ASPH with a length of 26mm is 29mm shorter. On the other hand, there is no difference between the max diameters of these lenses, both coming at 63mm.
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, 51% (105g) lighter than the Panasonic 25mm F1.4 II ASPH's weight of 205g.
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 Panasonic 25mm F1.4 II ASPH and 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 Panasonic GH6, OM System OM-1 and Panasonic GH5 II.
Focal Range
Panasonic 25mm F1.4 II ASPH is a prime lens with fixed focal lenght of 25mm which has a 35mm equivalent focal range of 50mm when used on a FourThirds format camera. Panasonic 20mm F1.7 ASPH is a prime lens with fixed focal lenght of 20mm which has a 35mm equivalent focal range of 50mm when used on a FourThirds format camera.