The EF 40mm f/2.8 STM is Canon’s pancake lens — 23mm long, 130 grams, and optically decent enough that photographers have been underestimating it for over a decade. On a mirrorless body via adapter, it pairs with something older than autofocus: zone focusing, the technique of pre-setting focus distance and shooting without confirming focus at all. The method is simple. Set the lens to manual focus via the adapter’s control ring or the camera’s MF button.