Telephoto lens
A telephoto lens, in
Construction
In contrast to a telephoto lens, for any given focal length a simple lens of non-telephoto design is constructed from one
But such simple lenses are not telephoto lenses, no matter how extreme the focal length – they are known as
A telephoto lens works by having the outermost (i.e. light gathering) element of a much shorter focal length than the equivalent long-focus lens and then incorporating a second set of elements close to the film or sensor plane that extend the cone of light so that it appears to have come from a lens of much greater focal length. The basic construction of a telephoto lens consists of front lens elements that, as a group, have a positive focus. The focal length of this group is shorter than the effective focal length of the lens. The converging rays from this group are intercepted by the rear lens group, sometimes called the "telephoto group," which has a negative focus. The simplest telephoto designs could consist of one element in each group, but in practice, more than one element is used in each group to correct for various aberrations. The combination of these two groups produces a lens assembly that is physically shorter than a long-focus lens producing the same image size.
This same property is achieved in camera lenses that combine mirrors with lenses. These designs, called catadioptric, 'reflex', or 'mirror' lenses, have a curved mirror as the primary objective with some form of negative lens in front of the mirror to correct optical aberrations. 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. The mirrors also fold the light path. This makes them much shorter, lighter, and cheaper than an all refractive lens, but at the cost of some optical compromises due to aberrations caused by the central obstruction from the secondary mirror.
The heaviest non-Catadioptric telephoto lens for civilian use was made by
The telephoto lens design has also been used for wide angles, at least once in the case of the Olympus XA where it permitted a 35 mm focal length to fit in an extra compact camera body.[4]
Retrofocus lenses
Naming
Telephoto lenses are sometimes divided into the further sub-types of short or portrait (85–135 mm in 35 mm film format),[5] medium (135–300 mm in 35 mm film format) and super (over 300 mm in 35 mm film format).[6]
Short / Portrait | Medium | Super | |
---|---|---|---|
Angle of view (diag.) | 34–18° | 18–8° | 8–1° |
1" | 25–50 | 50–110 | 110–735 |
4/3 | 35–65 | 65–150 | 150–1000 |
APS-C | 45–90 | 90–195 | 195–1310 |
35 mm | 70–135 | 135–300 | 300–2000 |
6×6 (120 film) | 130–250 | 250–550 | 550–3660 |
4×5 (large format) | 550–1000 | 1000–2250 | 2250–15000 |
History
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.[8]
Histories of photography usually credit Thomas Rudolphus Dallmeyer with the invention of the photographic telephoto lens in 1891, though it was independently invented by others about the same time; some credit his father John Henry Dallmeyer in 1860.[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
McKay presented his work to the Wellington Philosophical Society (the precursor of the Royal Society of New Zealand) in 1890.[12]
See also
References
- ^ ISBN 978-1-136-09118-6.
- ISBN 978-0-8194-6093-6.
- ^ "Zeiss Apo Sonnar T* 1700 mm F4 lens". Digital Photography Review. Retrieved 1 October 2006.
- ^ "XA The Original". www.diaxa.com. Retrieved 2017-02-08.
- ^ Dam, Peter (November 7, 2022). "FAQ: What is a Portrait Lens?". Adorama. Retrieved 18 October 2023.
- ^ "Wide-Angle vs. Telephoto: Which Lens Should You Choose?". 13 April 2021.
- ^ Edward John Wall and Thomas Bolas (1902). The Dictionary of Photography for the Amateur and Professional Photographer. London: Hazell, Watson, and Viney Ld.
- ISBN 978-3-540-40106-3.
- ISBN 978-0-312-31367-8.
- ^ Simon Nathan (2018). "Alexander McKay: New Zealand's first scientific photographer". Tuhinga. 29: 35–49.
- ISBN 978-1-877372-22-3.
- ^ Alexander McKay (1891). "On Some Means for increasing the Scale of Photographic Lenses, and the Use of Telescopic Powers in Connection with an Ordinary Camera". Transactions of the New Zealand Institute. XIII: 461–465.
External links
- Information on Catadioptric mirror lenses
- Further clarification: Why Telephoto?
- 3 part series on Cheap Super Telephoto Lenses (300-500mm)
- Stanford University CS 178 interactive Flash applet showing how a telephoto zoom lens works.