also: ピントガラス
Refers to glass with a roughened surface used for diffusing light or as a focusing aid in cameras. Often used in optical and photographic contexts.
from Dutch brandpunt glas
See also: すりガラス
Ground glass is used to diffuse light.
focusing screen
Specifically the ground-glass screen in a camera viewfinder used for manual focusing. Common in photography terminology.
Focus using the focusing screen of an old camera.