Focusing Device

2-4-050

Alternative term: Focuser (G.B.)

An optical device used for focusing (2-2-155), for example, a short telescope with cross-wire, fixed to the frame of the optic.

Note: In France and Germany, the type of focusing device mainly used projects, by means of lenses and prisms, an image of the luminous element of the light source on a screen fitted with a cross-wire and usually also with concentric rings.

Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)

English