Focus peaking is an EVF overlay that highlights in-focus edges in a selected color — typically red, yellow, or white — as you rotate the focus ring. It is a mirrorless-native feature, unavailable on optical viewfinders by definition, and it changes the character of manual focus work on modern cameras in ways that make the technique accessible where it was previously a specialist skill. The RF 35mm f/1.8 IS Macro STM has a smooth, well-damped manual focus ring with enough rotation travel to be used precisely.