Zoom lens
For example, all zoom lenses suffer from at least slight, if not considerable, loss of image resolution at their maximum aperture, especially at the extremes of their focal length range.
Quality degradation is less perceptible when recording moving images at low resolution, which is why professional video and TV lenses are able to feature high zoom ratios.
High zoom ratio TV lenses are complex, with dozens of optical elements, often weighing more than 25 kg (55 lb).
[5] Some digital cameras allow cropping and enlarging of a captured image, in order to emulate the effect of a longer focal length zoom lens (narrower angle of view).
In addition, the afocal part of a zoom lens can be used as a telescope of variable magnification to make an adjustable beam expander.
Early forms of zoom lenses were used in optical telescopes to provide continuous variation of the magnification of the image, and this was first reported in the proceedings of the Royal Society in 1834.
[7]: 156 The most impressive early TV Zoom lens was the VAROTAL III, from Rank Taylor Hobson from UK built in 1953.
[8] The first modern film zoom lens, the Pan-Cinor, was designed around 1950 by Roger Cuvillier, a French engineer working for SOM-Berthiot.
In 1956, Pierre Angénieux introduced the mechanical compensation system, enabling precise focus while zooming, in his 17-68mm lens for 16mm released in 1958.
[7]: 167 There are many possible designs for zoom lenses, the most complex ones having upwards of thirty individual lens elements and multiple moving parts.
At each of the three points shown, the three-lens system is afocal (neither diverging or converging the light), and hence does not alter the position of the focal plane of the lens.
Between these points, the system is not exactly afocal, but the variation in focal plane position can be small enough (about ±0.01 mm in a well-designed lens) not to make a significant change to the sharpness of the image.
Modern optical design techniques have enabled the construction of zoom lenses with good aberration correction over widely variable focal lengths and apertures.
Although modern design methods have been continually reducing this problem, barrel distortion of greater than one percent is common in these large-ratio lenses.
