The effect of focal length changes with camera format
Digital photography includes three major image formats. A specific focal length is meaningless without knowing the format, which is based on sensor size. For example, a 35mm lens is always 35mm, but depending on the format, it could be a wide-angle lens, a normal lens, or even a telephoto. Traditionally, lenses have been categorized by wide-angle, normal and telephoto. Today, they include super-wide, fisheye, short telephoto, medium telephoto, long telephoto, and even super-telephoto. Each refers to a specific way a focal length projects the world onto a sensor.