some people like to use manual focus...but its hard to do on these EF and EF-S pancake's....as the focus ring is tiny!! This adapter is a nice press fit @ 0.30mm layering height.... I have sanded and air blown the adapter, to make sure there is no dust or debris on it.... you will need to switch to 'manual' before fitting, and you need to remove to change lens.... works on the EF-40mm f2.8 STM and EF-S 24mm f2.8 STM pancake lens's