Electronic focusing
Manual doesn’t always mean mechanical
The majority of Canon’s EF and EF-S ‘USM’ (Ultrasonic Motor) lenses for EOS DSLRS have a physical connection between the focusing ring and the focusing optics. There are exceptions though, such as the EF 85mm f/1.2l II USM and the EF-S 18-135mm f/3.5-5.6 IS USM, both of which utilize electronic manual focusing instead.
Electronic focusing is a focus-by-wire system, where the camera adjusts the focusing distance via a motor when you turn the focusing ring. Lenses that are designed for the mirrorless EOS R System, as well as DSLR lenses that are equipped with an ‘STM’ (Stepping Motor) instead of a USM, also only offer electronic focusing.
One of the potential drawbacks with an electronic focusing ring is that isn’t as tactile; there can be a lag between the ring being rotated and the focus distance changing. It can be very subtle, but it’s typically more noticeable on STM lenses than those that are fitted with the newer Nano USM motors. The electronic-only connection means that the camera has to be powered on for manual focus to work too.
An electronic focusing ring has some advantages though.
You can change how it operates via the ‘Lens electronic MF’ or ‘Electronic full-time MF’ options, if they’re available in your camera’s menu. You can choose whether manual focusing is disabled when the lens focus switch is set to AF, for example. This is can be handy if you don’t want to inadvertently adjust the focus ring when you’re supporting the lens, or if manual focus is enabled up until One Shot AF has achieved focus. Most EOS R System cameras also give you the chance to change the sensitivity of the electronic focusing ring on RF lenses. By default, the sensitivity is linked to the rotation speed – so the faster you turn the ring, the greater the focus adjustment – but you can link it to the degree of rotation instead.