What 1mm at f/1.4 actually gives you
At 1mm this sits in ultra-wide territory, where straight lines near the frame edge stretch noticeably and a small step forward changes the composition a lot.
The f/1.4 maximum aperture is about as fast as production lenses get: it gathers a lot of light and throws backgrounds well out of focus, at the cost of a depth of field thin enough that focus accuracy starts to matter on close subjects.
Size and weight
At 130g (4.6 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.
Stabilisation
There is no optical stabilisation in the lens, so handheld steadiness depends on the body having IBIS, or on keeping the shutter speed up.
