AUTOFOCUS
There are two main types of AF on offer in this group. Here’s how they work
M any of Canon’s latest lenses use STM (Stepping Motor) systems, which are incredibly quiet and also enable smooth focus transitions when shooting video. Lenses with the lead-screw STM variant can autofocus in almost complete silence, whereas smaller lenses that feature ‘gear type STM’ with gearwheels tend to be more audible and less speedy.