The type of photography that you are planning to use is an important decision factor. Here we have evaluated the Canon RF 135mm F1.8 L IS USM and the Olympus ED 75mm f1.8 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. Canon RF 135mm F1.8 L IS USM is the longer of the two lenses at 130mm. The Olympus ED 75mm f1.8 with a length of 69mm, is 61mm shorter. Besides being longer, the Canon RF 135mm F1.8 L IS USM also has a larger diameter of 89mm compared to the Olympus ED 75mm f1.8's 64mm 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. Olympus ED 75mm f1.8 weighs 305g, 67% (630g) lighter than the Canon RF 135mm F1.8 L IS USM's weight of 935g.
Lens Mounts
The Canon RF 135mm F1.8 L IS USM has the Canon RF lens mount whereas the Olympus ED 75mm f1.8 has the Micro Four Thirds lens mount. Some of the latest released cameras that are compatible with these mounts are Canon R8, Canon R50 and Canon R6 II for the Canon RF Mount and OM System OM-5, Panasonic GH6 and OM System OM-1 for the Micro Four Thirds Mount.
Focal Range
Canon RF 135mm F1.8 L IS USM is a prime lens with fixed focal lenght of 135mm. When it is mounted on an APS-C sensor camera with 1.6x crop, it provides a 35mm (FF) equivalent of 216mm.
Olympus ED 75mm f1.8 is a prime lens with fixed focal lenght of 75mm which has an effective (full-frame 35mm equivalent) focal range of 150mm when used on a FourThirds format camera.