Zoom lens
A zoom lens or short zoom is a lens with variable focal length.
Designations
It says " Zoom" when the zoom lens, and " Zoom" if the zoom action is meant. "Zoom" is an English, onomatopoeic description ( onomatopoeia ) for fast motion, such as " Hush " in German. The size of the work area ( focal length ) of a zoom lens is described by the zoom factor.
Also common designations such as varifocal lens or Vario system, rubber lens ( in the 1970's in use, now unusual ), rare ( the ) Transfokar or ( the ) Transfokator. The technically correct term for such lenses is pancratic system ( from Ancient Greek pan = all and kratos = power, that is to say: an " all-powerful ", over all focal lengths operative optical design ).
Zoom lens and zoom lens are different names for the same type of lens, as it is also reflected in the lens name (version engravings ). While the zoom and varifocal lenses hold constant the image distance when changing the focal length, the image distance changes significantly with the varifocal lenses previously isolated offered, which makes an adjustment of the sharpness necessary. After the autofocusing ( AF) had prevailed, a slight change in the image distance is accepted at the focal female bodies and thus relieves the burden on the optical correction with many zoom and varifocal lenses.
Function
The displacement of lens elements in the lens ( by rotating or sliding a ring on the lens or pressing a zoom button on motor -driven zoom, for example, from compact cameras ) causes a change of the focal length. With high quality cameras so that a continuous adjustment of the crop to the subject is possible, as often digitally graded in some simpler models analogous only more or less coarse. Some cameras and lenses, it is possible to activate a so-called step zoom, in which only some typical focal lengths can be selected, which can be very useful, for example in the making of panoramas.
Zoom lenses are a cost- and weight-saving alternative to a set of lenses with fixed focal length, covering the range from wide angle to telephoto lenses. As opposed to a fixed focal length lens does not have a focal length, but the covered focal length range is indicated on the lens (eg 35-80 mm or 80-200 mm). Zoom lenses can also be used to advantage, if no time ( fast changing subjects) or opportunity (dust, sand, moisture, underwater, mountain climbing, etc.) for a lens change.
However, zooming only changed the picture, but not the recording perspective. The convenient handling seduces inexperienced photographers easy to neglect this important design agent in photography. When the film is about to replace a tracking shot zoom in any case. However, many creative designs in the film industry can only be achieved with zoom, such as a tracking shot with a simultaneous zoom.
Zoom from moderate wide- angle range to slight telephoto (in the small format about 35 mm to 80 mm or 115 mm ) are more and more often to the basic equipment of system cameras; with compact digital cameras they have become virtually standard. For system cameras, there are also pure wide-angle or telephoto zoom. Lenses with a zoom factor of more than five are often referred to as a super zoom ( examples: 28-200 mm or even 18-200 mm).
Zoom lenses with electromechanical adjustment of the focal length range are sometimes called power zoom.
Properties
The design and manufacture of zoom lenses is more complex and costly than that of fixed focal length lenses. Thus, apart from high-performance zoom lenses such as the manufacturer Cooke or Angénieux that find their use, especially in the film market and cost- high five -figure sums, the imaging performance of zoom lenses usually worse than the lenses with a fixed focal length, since their manner of construction always forces a compromise between the necessary corrective lenses for the individual focal lengths. In addition, zoom lenses are usually fainter, ie: the minimum f-number is larger. In the small picture format are approximately 4.5-5.6 at 28-100 mm lenses ( be separated from 2.8 to 2.0 is reached) typical, whereas fixed focal length lenses have an aperture ratio of 1:2.8 to 1:1.4 ( achieve 1:0.95 ) in extreme cases. For available- light photography zooms are therefore less suitable.
Exceptions to this are again the high-quality lenses in the film industry, often provide the light intensities of 1:1.4 (and possibly even more light ).
In fact, only allowed the introduction of aspherical lenses (ie those that are not spherical segment ) the design satisfying pankratischer systems, which cover a larger zoom factor than about 3:1, especially at zoom that extend into the wide-angle range. The enormous computational effort in the design of optics with aspherical elements - some with ten or twelve individual lenses ( and a corresponding number of refracting surfaces ) - was again only be solved with computer technology.
Many very compact designed digital cameras have zooms that are motorized retractable into the camera body. In these designs often compromise between optical requirements and the need for compactness must be made so that in such models, lens errors are often not optimally corrected out and clearly visible chromatic aberrations and distortions massive occur particularly in the wide- angle range. Some cameras offer correction functions for the compensation of these errors already when you save the recordings.
The offered at many zoom macro function for close-ups replaced qualitatively no specially for very large scales calculated "real" macro lens. In particular, the field curvature and the geometric distortions lead at close range often totally inadequate image quality, so that, for example, repro photography are not useful feasible.
In the film sector, however, numerous creative possibilities through the use of zoom lenses that are not possible with fixed focal length. Hitchcock, for example combined in his film Vertigo a tracking shot with a zoom, which produced a dynamic, troubling aspect ratio change in the scene. This design now bears the nickname " Vertigo effect" (→ Dolly Zoom). Other heavy users of the zoom effect such as Sergio Leone, Stanley Kubrick and Peter Jackson have created a variety of artistic designs which can only be realized with zoom optics.
In the zoom cinema and movie production used are the most expensive acquisition union lenses, significantly more expensive than fixed focal lengths. The widely used for feature film zooms the Angénieux - Optimo Series cost at present (2010) more than 60,000 euros. Since they are custom-made, as a rule, the delivery times are often more than one year.
History
A first immediate predecessor of the zoom lens was developed in 1928 by Hugh Ivan Gramatzki, manufactured by Siemens Transfokator. One of the first zoom lenses for the mass market in the photographic sector was the Zoomar 2.8 / 36-82 by Voigtländer, introduced in 1959. Numerous similar constructions for SLR cameras followed. Today lenses can find with electric drive components also in simpler small cameras.
In the film and television sector Lenses solved with variable focal length from the lens turret previously frequently used. For decades dominated television cameras with the well-known box-shaped paneled, retractable lenses as needed, each with a fixed focal length, the professional television production. When Super-8 cine film format, found early varifocal lenses sometimes very high light intensity, since artifacts fell into the weight at the system-related limitations of the format less.
Digital Zoom
The digital zoom is not true, ie optical, zoom. This is only cut out part of the image in principle and extended by interpolation to the full size, which is associated with more or less distinct in quality. In most cases it is advisable to dispense with the digital zoom and to create the image on the computer manually.
Compared to the eye
The eye to change its focal length only in terms of focusing. When viewing distant objects the brain focused on this and ignores the edge; pick up the object but it can not; so far is the distance vision of man with a digital zoom comparable.
Stylistic devices
The Dolly Zoom, and Vertigo effect, called cinematic style means sets a tracking shot with simultaneous counter-rotating Zoom on: The center remains unchanged while the perspective shifts at the edges, almost as if the audience drive into a tunnel, but the end is not approaches. A typical application is the representation of a case of vertigo.