Originally posted by: pontifex
whats the difference between a macro lens and a telephoto lens?
i believe my 70-300mm tamron lens says macro telephoto on it...
A macro lens is one optimized for closeups. Most LF macro lenses are optimized for 1:1, which means image size = subject size. Because the angles of the light rays from the subject to the lens are different for different distances to the subject, the optical corrections of a lens vary with the distance to the subject. This means that a lens design will be best for one particular subject distance. (It doesn't say how much worse the lens will perform at other subject distances -- it could be essentially just as good, or much worse.) Most lenses are optimized for distant subjects. Macro lenses are optimizied for near subjects. The LF macro lenses that I know of need the regular bellows draw -- about one focal length for distant objects and about two focal lengths for life size imaging. (I say "about" becaue the nodal points may be a few mm off from the center of the lens.)
Many photographers use "telephoto" to mean any long lens -- "long" meaning a focal length longer than the diagonal of the format. The correct meaning of the term is a lens that needs significantly less extension than its focal length. An optical design is used that positions the rear nodal point in front of the center of the lens. When a lens is focused on infinity, the distance from the image to the rear nodal point is one focal length, so having the rear nodal point in front of the lens moves the lens back, reducing the extension required.