focal ratio

noun Optics, Photography.

f-number.

Origin of focal ratio

First recorded in 1925–30

Words nearby focal ratio

focal infection, focal length, focal necrosis, focal plane, focal point, focal ratio, focal reaction, focal segmental glomerulosclerosis, focal seizure, focal-plane shutter, focalize

British Dictionary definitions for focal ratio

focal ratio

noun

photog another name for f-number