>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:? Steve. If only all questions were so simple. The "lense speed" is the ratio of the focal length to the maximum aperture diameter - at infinity focus ;o) The ":" is just the traditional way of expressing a ratio So for a 100mm f2.8 lens, the maximum aperture will be 36mm across. In comparison, for a 20mm f2.8 lens, the maximum aperture will be only 7mm across. Actually, it does get more complicated when you go in to it, but ... I'll leave that for others to confuse the issue with ;o) Bob
