I know this is a basic question, but I have not been able to find an answer searching the Internet. What exactly is meant by the 28-128 mm range? I know the higher the number the closer the image, but what is it that is being measured? Thanks.

-- Brock Vila (brockvila@aol.com), June 04, 2002

Answers

Essentially it's the distance from the film to the optical center of the lens (Actually the front node of the lens, or some such thing.) when the lens is focused to infinity. This is usually expressed in milimeters (mm), but on some, mostly older lenses, it is expressed in inches. In any case it's the term used for the optical length of the lens.

Normal lens length is generally considered to be approximatly equal to the diagonal of the film's image area. The would make a 43mm lens the normal lens length for 35mm film, but for several old marketing and mechanical reasons, normal is considered to be 50mm.

Wide angle lenses are anything that is optically shorter than the normal lens. They see a wider angle of view since the optical node is closer to the film. A longer lens sees a narrower view, but everything it does see is just that much larger on the film.

-- Jim Strutz (j.strutz@gci.net), June 04, 2002.

Jim, thank you.

-- Brock Vila (brockvila@aol.com), June 05, 2002.