In photography and cinematography, a telephoto lens is a specific construction of a long focal length photographic lens that places its optical center outside of its physical construction, such that the entire lens assembly is between the optical center and the focal plane. Photography (fә'tɒgrәfi or fә'tɑːgrәfi (from Greek φωτο and γραφία is the process and Art of recording pictures by means of capturing See also Filmmaking Cinematography (from Greek: kinesis κινησις (movement and grapho γραφω (to record is the discipline A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis A regular lens of a focal length that is longer than what is considered a normal lens is not necessarily a telephoto lens. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. In Photography and Cinematography a normal lens is a lens that generates images that generally look "natural" to a human observer under normal A telephoto lens has to incorporate a special lens group known as a telephoto group (see below); nevertheless, non-telephoto lenses of long focal length are often informally referred to as telephoto lenses. The angle of view created by a telephoto lens is the same as that created by an ordinary lens of the same specified focal length. In Photography, angle of view describes the angular extent of a given scene that is imaged by a Camera.
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Construction
If a camera lens were to be constructed from a single lens of 200 mm focal length, then when the lens is focused on an object at infinity, the lens will be 200 mm away from the focal plane where the film or sensor is. A camera is a device used to capture images either as still Photographs or as sequences of moving images ( Movies or Videos. The center of the lens is referred to as the optical center of the lens. Even constructing the lens out of multiple elements in the regular fashion, usually to eliminate aberrations, will still have the optical center within the construction. Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics.
As the focal length of such lenses increases, the physical length of lens becomes inconveniently long. But such lenses are not telephoto lenses, no matter how extreme the focal length. They are simply known as long focal length lenses.
The diagram to the right shows the basic construction of a telephoto lens. It 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 with mirrors combined with lenses in catadioptric designs. A catadioptric optical system is one which contains both lenses and Mirrors Catadioptric systems are commonly used in Telescopes and in lightweight The mirrors in such designs fold the light path and the curved secondary extends the light cone, making the lens much shorter than the focal length even given the folded design. However, lenses incorporating mirrors are not necessarily of telephoto design.
Compare with the opposite effect used in retrofocus lenses, sometimes described as 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. The Angénieux retrofocus Photographic lens is a Wide-angle lens design that uses an inverted telephoto configuration Zoom lenses that are telephotos at one extreme of the zoom range and retrofocus at the other are now common. A zoom lens is a mechanical assembly of lens elements with the ability to vary its Focal length (and thus Angle of view) as opposed to a fixed focal
The heaviest telephoto lens was made by Carl Zeiss and has a focal length of 1700 mm with a maximum aperture of f/4, implying a 425 mm (16. Carl Zeiss ( September 11, 1816 &ndash December 3, 1888) was an Optician commonly known for the company he founded Carl Zeiss 7 inch) entrance pupil. In an optical system the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light It is designed for use with a medium format Hasselblad 203 FE camera and weighs 256 kg (564 lb). This page is about medium-sized film formats For formats of a different Medium, see Format disambiguation Victor Hasselblad AB is a Swedish manufacturer of Medium-format Cameras and photographic equipment based in Gothenburg, Sweden [1]
Effects
Telephoto and other long-focal-length lenses are best known for making distant objects appear magnified. Magnification is the process of enlarging something only in appearance not in physical size This effect is similar to moving closer to the object, but is not the same, since perspective is a function solely of viewing location. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or Two images taken from the same location, one with a wide angle lens and the other with a telephoto lens, will show identical perspective, in that near and far objects appear the same relative size to each other. Comparing magnification by using a long lens to magnification by moving closer, however, the telephoto shot appears to compress the distance between objects due to the perspective from the more distant location. Long lenses thus give a photographer an alternative to the type of perspective distortion exhibited by shorter focal length lenses where (when the photographer stands closer to the given subject) different portions of a subject in a photograph can appear out of proportion to each other. In Photography and Cinematography, perspective distortion describes one of two phenomena – the appearance of a part of the subject as abnormally large relative
Long lenses also make it easier to blur the background more, even when the depth of field is the same; photographers will sometimes use this effect to defocus the background in an image to "separate" it from the subject.
Still photography
Effect of different focal lengths on photographs taken from the same place:
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The above photos were taken using a 35 mm camera, using lenses of the given focal lengths. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light.
Constant object size
The photographer often moves to keep the same image size on the film for a particular object. Observe in the comparison images below that although the foreground object remains the same size, the background changes size; thus, perspective is dependent on the distance between the photographer and the subject. The longer focus lenses compress the perception of depth, and the shorter focus exaggerate it. [2] The perspective of the so-called normal lens, 50mm focal length for 35 mm film format, is conventionally regarded as a "correct" perspective, though a longer lens is usually preferred for a more correct perspective for portraits.
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History
The concept of the telephoto lens, in reflecting form, was first described by Johannes Kepler in his Dioptrice of 1611 [1], and re-invented by Peter Barlow in 1834. Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer For the Coronation Street character of the same name see Peter Barlow (Coronation Street Peter Barlow ( October 15 [2]
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. Thomas Rudolphus Dallmeyer (1859-1906 English optician was the son of John Henry Dallmeyer who ran an optics business John Henry Dallmeyer ( September 6, 1830 - December 30, 1883) Anglo-German optician, was born at Loxten, Westphalia [3]
See also
References
- ^ "The World's Largest Telephoto Lens". A film format is a technical definition of a set of standard characteristics regarding image capture on Photographic film, for either stills or movies Secret photography involves a person or persons being unaware that they are being intentionally photographed Press release. A news release, media release, press release or press statement is a written or recorded Communication directed at members of the News
- ^ Bill Smith (2001). Designing a Photograph: Visual Techniques for Making Your Photographs Work. Amphoto Books. ISBN 0817437789.
External links
- Information on Catadioptric mirror lenses
- Further clarification: Why Telephoto?
- 3 part series on Cheap Super Telephoto Lenses (300-500mm)
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