Review by Klaus Schroiff, published April 2021

Introduction

The build quality of this tiny lens is good but it's obvious that it doesn't target professional users. There is no weather-sealing and an inner lens tube extends when focusing towards closer distances. The tube retracts automatically when switching off the camera (unless you disable this via the camera settings). A curious aspect is the focus/control ring. Usually, Canon R-mount lenses feature a dedicated, configurable control ring. On the RF 50mm f1/8 STM there's a single ring (textured like the usual control ring) that combines both aspects and you can select the mode via a switch on the lens. A lens hood is not provided.

Rather than using a USM drive, Canon opted for the STM (Stepping motor) variant here. The AF speed is still quite quick (in good light conditions) but it's not noiseless. Even if you argue that Canon had to apply cost-cutting measures, it is strange that they weren't able to come up with a noiseless AF stepping motor just like everybody else. Manual focusing is possible via the usual "by-wire" system so you drive the AF motor when turning the focus ring. The close-focus capabilities have been slightly "improved" (more on this later) compared to it EF-mount cousin - the maximum object magnification is now rated at 1:4 vs 1:5 for the older lens. An optical image stabilizer is not implemented. Canon is pointing out that the in-camera IS (e.g. on the R6/R5) is good enough for a gain of 7 f-stops with this lens. While this may be true by CIPA standards, you should expect less than that in real life.