Telephoto lens

This second group of elements spread the cone of light so that it appears to have come from a lens of much greater focal length.

They also use a curved secondary mirror to relay the image that extends the light cone the same way the negative lens telephoto group does.

This makes them much shorter, lighter, and cheaper than an all refractive lens, but some optical compromises, primarily the "doughnut" shape of out-of-focus highlights, are caused by the central obstruction from the secondary mirror.

It is designed for use with a medium format Hasselblad 203 FE camera and weighs 256 kg (564 lb).

These are called retrofocus lenses or inverted telephotos, which have greater clearance from the rear element to the film plane than their focal length would permit with a conventional wide-angle lens optical design.

[6] The concept of the telephoto lens, in reflecting form, was first described by Johannes Kepler in his Dioptrice of 1611,[7] and re-invented by Peter Barlow in 1834.

[9] In 1883 or 1884, New Zealand photographer Alexander McKay discovered he could create a much more manageable long-focus lens by combining a shorter focal length telescope objective lens with negative lenses and other optical parts from opera glasses to modify the light cone.

One of McKay's photographs shows a warship anchored in Wellington harbour about two and a half kilometres away, with its rigging lines and gun ports clearly visible.

[10] The other, taken from the same point, is of a local hotel, the Shepherds Arms, about 100 metres distant from the camera.

A collection of telephoto lenses
A 500 mm non-telephoto long-focus lens with a physical length about the same as its focal length.
A 150–500 mm telephoto zoom lens, physically much shorter than its maximum focal length.
Diagram of a typical telephoto lens with a large positive lens and a smaller negative telephoto group combined to create a much longer focal length - f .
Diagram of a catadioptric mirrors lens.
A diagram of light travel through a wide-angle lens showing how focal length can be shorter than the lens.
A Canon New F-1 (1981), a 35 mm camera with a telephoto zoom lens with 70-210 mm focal length.
Some compact digital cameras like the Panasonic Lumix DMC-TZ18 (2010) have superzoom lenses with a large range of focal lengths. The lens is completely stored inside the camera in switched-off state and has a maximum focal length (shown) of 384 mm (calculated equivalent to 35 mm film ), minimum is 24 mm, a zoom factor of 16×.