telephoto lens


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telephoto lens

a compound camera lens in which the focal length is greater than that of a simple lens of the same dimensions and thus produces a magnified image of a distant object

Telephoto Lens

 

a photographic lens with a focal length that is longer than normal, in which the distance between the front surface of the first lens and the back focal plane is shorter than in other types of long-focus lenses. This feature permits a reduction in the overall size of still and motion-picture cameras. Telephoto lenses are used in producing large-scale photographs of distant objects and for portraits.

Figure 1. Diagram of a two-element telephoto lens: (H′) back principal plane, (F′) back focal plane, (D1) converging element, (D2) diverging element, (L) distance from the front surface of the lens to the back focal plane, (f′) back focal distance

The most common designs for telephoto lenses make use of two components (Figure 1), each consisting of a group of lenses; the first group is a converging system, and the second is a diverging system. The components are combined in such a way that the back principal plane H’ is moved forward of the lens and the distance L is shortened. The shortening index Kt = L/f′ In some telephoto lenses, the focusing distance of the second group of lenses is positive, and Kt is close to unity. Such lenses are considered three-group systems.

L. A. RIVKIN

telephoto lens

[¦tel·ə¦fōd·ō ′lenz]
(optics)
A lens for photographing distant objects; it is designed in a compact manner so that the distance from the front of the lens to the film plane is less than the focal length of the lens.
References in periodicals archive ?
By increasing the upper sizing limit of Insitec technology from 1000 [micro] to 2500 [micro], Malvern's new telephoto lens broadens access to reliable continuous laser diffraction particle size measurement, enabling customers to tackle new applications and increase the efficiency of current systems-Additional benefits include improved stability and ease of alignment, better vibration tolerance, robustness to temperature, and reduced space requirement without compromising measurement quality at lower size limits.
Steve, whose wife, son and two nephews are also volunteers at the station, said: "It was pretty rough that day and I spent half an hour trying to get pictures before moving a bit further away and putting on a telephoto lens.
Armed with his telephoto lens and a great love for the the game, Colon has been perched in his spot, way out in the outfield, capturing the drama of the games of the Amateur Softball Association's season.
This has tremendous advantages for longer lenses: a telephoto lens with a nominal focal length of 200mm in the 35mm format has a working focal length of 320mm when attached to a digital SLR.
Using a long telephoto lens to narrow the zone of focus, and spot metering the subject to expose the highlights along the side of the horse's face, I bring out the facial muscles and arteries, as well as the detail on the bridle, to convey a sense of power.
With the powerful 20-60x zoom and the ability to double as an 800mm telephoto lens, this one is very hard to send back.
Inspired by a lifelong love for animals, Brandt insists on never using a telephoto lens in portraying them.
Camera and film: Bring a camera with a telephoto lens that does not require fiddling, as animals do not always stand still.
Still camera with telephoto lens, adequate supply of film or other removable medium, and spare battery
The impact of the more compact lens size will be especially marked on telephoto lenses, making it possible to produce a Four Thirds System 300mm telephoto lens, for example, that offers performance equivalent to an approximately 600mm lens on a 35mm film SLR camera.
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The Digibino DB100 binoculars are capable of seven times magnification - equivalent to a 280-millimetre telephoto lens.