Photographers talk about 大光圈 (wide/large aperture, small f-number like f/1.4) and 小光圈 (narrow/small aperture, large f-number like f/16). Counterintuitive: a larger aperture number actually means a smaller opening.
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光 (light) + 圈 (ring/circle) — literally 'light ring,' the circular opening that lets light through.