Steve Ross <steveross.effigy@virgin.net> writes: > Hi > > Could someone explain these certain numbers found > around the front elements of a lens: 1:2.8 or 1:3.5 etc. > I know the 2.8 and 3.5 is the lense speed? but whats > the 1:? Yes: "2.8" isn't a speed, it's a number, and writing the lens aperture as (e.g.) "F2.8" confuses what is going on. The f-number means the lens aperture expressed as a fraction of the focal length (f), so f/2.8 means that the effective diameter of the lens aperture is the focal length divided by 2.8. Since this is a ratio, it's equally possible to represent it by a colon, and I believe this is the customary way to write the maximum aperture of the lens itself, around the rim. So 1:2.8 means the ratio of aperture to focal length is 1:2.8. Brian Chandler ---------------- geo://Sano.Japan.Planet_3 Jigsaw puzzles from Japan at: http://imaginatorium.org/shop/
