Full-time manual focus

Change the focus distance without leaving AF mode

Many lenses offer what’s known as ‘full-time manual focus’. This means that you can twist the focus ring even when the lens is set to AF and fine-tune the point of focus. You can do this at any point before, during or after the camera’s autofocus routine. Not all lenses offer this feature, and you risk damaging these if you manually focus while the lens slider is set to AF.

It only makes sense to do this when the camera is set to One Shot AF mode; in AI Servo or AI Focus mode the camera will simply try and refocus the lens if it detects that the area under the active AF point isn’t sharp. One way around this is to use back-button focusing so that pressing the shutter release to take a photo won’t trigger the autofocus system. The Custom Controls option in the Custom Functions menu enables you to set up your DSLR so that holding one of the buttons on the rear of the camera will either activate the autofocus or deactivate it. Either way, it means that you can suspend the camera’s continuous autofocus and tweak focus manually.

There is a compromise to focusing manually without sliding the switch on the lens to MF: the focus indicator in the viewfinder won’t indicate when the manually focused image is sharp.

Ring USM You can use full-time manual focus override with all Canon’s L-series autofocus lenses as well as some ‘consumer’ models. STM These lenses also offer full-time manual focus override, although shutter release has to remain half-pressed to make...

Micro USM Lenses with this type of motor don’t offer manual focus override, with the exception of a few that use a clutch mechanism.