Back-Button Focus: RF 24-105mm f/4L IS USM as a Daily Driver
Back-button focus separates autofocus activation from shutter release. The shutter half-press no longer engages AF. Instead, the AF-ON button on the rear of the camera acquires and holds focus. It is the single camera configuration change that most noticeably improves shooting consistency, and the RF 24-105mm f/4L IS USM — the kit lens for most R5 and R6 kits — is where most photographers should learn it.
The mechanics: hold AF-ON to focus continuously on a moving subject. Release AF-ON and the focus locks at that distance. Half-press the shutter, recompose, fire — the focus does not move, because the shutter press no longer controls it. This eliminates the need to switch between One-Shot and Servo AF modes. Holding AF-ON is Servo. Releasing it is One-Shot. One button. Two behaviors.
The RF 24-105mm is a practical lens for learning this because it covers a range — 24mm to 105mm — across which you regularly encounter both static and moving subjects within a single session. Architecture at 24mm, a street scene at 35mm, a face at 85mm, a distant detail at 105mm. If you are managing focus modes manually through that range, you are spending cognitive bandwidth that should be on the image. Back-button focus removes the mode-switch decision entirely.
Setup on any Canon R-series body: go to Custom Controls > Shutter button and disable AF. Then confirm AF-ON is set to Metering and AF start. The transition period is approximately two to four shooting sessions. After that, returning to half-press AF feels like the inferior system it is.
The technique pays dividends especially in street and event photography, where a subject that was moving stops, and you want the focus locked on that stillness without switching modes. You release AF-ON. The focus freezes. You fire.
This is not a complicated technique. It requires reconfiguring one button and then not thinking about it again.