ABSTRACT
An afocal attachment of the telescopic type is given by the separation of a pair of lens elements by a distance numerically equal to the sum of their focal lengths, giving the principal planes at infinity, i.e. the device has no focal length. A telescope system placed in front of a camera lens, with both initially focused on infinity, gives an image magnified by a factor equal to the magnifying power of the telescope, while the image conjugate remains unchanged. Cameras with fixed lenses, such as simple compact automatic types or Twin-lens reflex varieties as well as digital cameras, commonly use both wide-angle and telephoto varieties. A positive supplementary lens can be used fitted in front of almost any lens to give a limited close-up focusing range. Supplementary lenses of negative power may be used both to increase and to decrease the effective focal length of a prime lens, and are used in different imaging arrangements.
