Lens range refers to the focal length or range of focal lengths of the lens supplied with a camera as quoted by the manufacturer, describing the optical reach and angle of view that the lens is capable of delivering. For zoom lenses, the lens range describes the span from the shortest to the longest focal length available - for example, a lens described as 28-105mm covers a range from moderate wide angle through to short telephoto - while for fixed focal length lenses, a single focal length figure describes the lens's sole working distance.
A direct and meaningful comparison of lens ranges between cameras using different film or sensor formats requires careful consideration, as the physical size of the recording medium has a fundamental influence on the effective angle of view produced by any given focal length. A lens of a specific focal length will produce a different angle of view depending on the size of the film or sensor it is used with - the smaller the recording area, the narrower the angle of view delivered by that focal length, effectively multiplying its apparent reach compared to the same focal length used on a larger format.
This relationship is particularly important when comparing lenses designed for APS film cameras, digital cameras with APS-C or smaller sensors, and conventional 35mm film cameras. Because APS film and the CCD or CMOS sensors used in many digital cameras are physically smaller than the 24x36mm frame of standard 35mm film, the focal lengths of lenses designed for or used on these formats are correspondingly shorter than the focal lengths that would produce an equivalent angle of view on a 35mm camera. A lens with a quoted focal length of 18mm on a digital camera with an APS-C sensor, for example, produces an angle of view equivalent to approximately 27mm on a 35mm film camera, due to the crop factor introduced by the smaller sensor size.
To allow meaningful comparison between lenses used on different format cameras, manufacturers typically quote a 35mm equivalent focal length alongside the actual focal length of the lens, expressing what focal length would be required on a 35mm film camera to produce the same angle of view. These 35mm equivalent figures provide a universally understood reference point that allows photographers familiar with the established visual language of 35mm focal lengths to immediately understand the practical angle of view and perspective characteristics of a lens regardless of the format it is designed for.