What 40mm at f/2.5 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/2.5 is the working standard for a fast lens — a stop or two of low-light headroom over a kit zoom, and noticeably more background separation.
Size, close focus and filters
At 173g (6.1 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.
It focuses to 25cm, which is close enough to fill the frame with small subjects.
Filters are 49mm — worth checking against what you already own, since polarisers and ND filters at this size are reusable across any other lens sharing the thread. A dedicated aperture ring gives direct control without going through a camera dial, which mostly matters for video work.
Autofocus, stabilisation and weather sealing
Autofocus is driven by an XD Linear 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.
The barrel is weather-sealed, so rain and dust are a manageable risk rather than a reason to pack up.
