Size and Weight Comparison
Size of a lens is an important deciding factor when comparing two lenses.Olympus 30mm F3.5 Macro is the longer of the two lenses at 60mm. The Olympus M 25mm F1.8 with a length of 41mm is 19mm shorter. Besides being longer, the Olympus 30mm F3.5 Macro also has a larger diameter of 57mm compared to Olympus M 25mm F1.8's 56mm diameter.
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. Olympus 30mm F3.5 Macro weighs 128g, which means it is 8g (6%) lighter than the Olympus M 25mm F1.8 which has a weight of 136g.
Both Olympus 30mm F3.5 Macro and Olympus M 25mm F1.8 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.
Olympus 30mm F3.5 Macro is a prime lens with fixed focal lenght of 30mm which has a 35mm equivalent focal range of 60mm when used on a FourThirds format camera. Olympus M 25mm F1.8 is a prime lens with fixed focal lenght of 25mm which has a 35mm equivalent focal range of 60mm when used on a FourThirds format camera.