What 40mm at f/2 actually gives you
40mm sits close to the way the eye takes in a scene, which is why this range tends to get used as a general-purpose focal length.
f/2 is fast enough to keep shutter speeds up in poor light and to separate a subject from its background clearly.
Size and filters
At 170g (6.0 oz) it is light enough that it stops being a decision — the kind of lens that stays on the body or in the bag without thought.
Filters are 52mm — worth checking against what you already own, since polarisers and ND filters at this size are reusable across any other lens sharing the thread.
Autofocus and stabilisation
Autofocus is driven by a Stepping motor.
There is no optical stabilisation in the lens, so handheld steadiness depends on the body having IBIS, or on keeping the shutter speed up.
