Nikkor 28-200 mm zoom lens, extended to 200 mm at left and collapsed to 28 mm focal length at right

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 length (FFL) lens. Nikkor is the brand of lenses produced by Nikon Corporation, including camera lenses for the Nikon F-mount. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. In Photography, angle of view describes the angular extent of a given scene that is imaged by a Camera. They are commonly used with still, video, motion picture cameras, projectors, some binoculars, microscopes, telescopes, and other optical instruments. A Still camera is a type of Camera used to take Photographs Traditional cameras capture light onto Photographic film. A video camera is a Camera used for electronic Motion picture acquisition initially developed by the Television industry but now common in other applications This article is about motion picture film cameras See Video camera for cameras which record images electronically A camera is a device used to capture images either as still Photographs or as sequences of moving images ( Movies or Videos. Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. An optical instrument either processes Light waves to enhance an image for viewing or analyzes light waves (or Photons to determine one of a number of characteristic

Applications

Canon PowerShot A720 IS 5. The Canon PowerShot A is a series of Digital cameras released by Canon. 8-34. 8 mm zoom on a compact digital camera, resulting in a 6x optical zoom

Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or "4×" zoom. The term superzoom or hyperzoom is used to describe photographic zoom lenses with very large focal length factors, typically more than 4× and ranging up to 10× and even 14×. The term hyperzoom or superzoom is used to advertise photographic Zoom lenses with unconventionally large focal length factors typically more than 4× and ranging This ratio can be as high as 100× in professional television cameras. ^[1] Currently, photographic zoom lenses beyond about 3× are not considered to have a quality on par with prime lenses, and constant fast aperture zooms (usually f/2. In film and photography a prime lens is either a Photographic lens whose Focal length is fixed as opposed to a Zoom lens, or it is the primary lens 8 or f/2. 0) are typically restricted to this range.

Photographic zoom lenses should not be confused with telephoto lenses, those with a narrow angle of view. Some zoom lenses are telephoto, some are wide-angle, and others cover a range from wide-angle to telephoto. Lenses in the latter group of zoom lenses, sometimes referred to as "normal" zooms, have displaced the fixed focal length lens as the popular one-lens selection on many contemporary cameras.

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). This is commonly known as digital zoom and results in a lower quality image than optical zoom, as no optical resolution is gained. Digital zoom is a method of decreasing (narrowing the apparent Angle of view of a digital photographic or video image Optical resolution describes the ability of an imaging system to resolve detail in the object that is being imaged Many digital cameras have both, an optical and a digital zoom, combining them by first using the optical, then the digital zoom, so does the Canon PowerShot A720 IS which provides 6x optical zoom, 4x digital zoom resulting in a 24x combined zoom as both are multiplied. The Canon PowerShot A is a series of Digital cameras released by Canon. The optical zoom in this case can be calculated by dividing 34. 8/5. 8 as it is written on the lens tube of the camera, resulting in the zoom factor 6.

In addition to its photographic use, the afocal part of a zoom lens can be used as a telescope of variable magnification to make an adjustable beam expander. Digiscoping is a method of obtaining photos using a Digital camera through a spotting scope Telescope or less often Binoculars. An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum Magnification is the process of enlarging something only in appearance not in physical size This can be used, for example, to change the size of a laser beam so that the irradiance of the beam can be varied. A laser is a device that emits Light ( Electromagnetic radiation) through a process called Stimulated emission. Irradiance, radiant emittance, and radiant exitance are Radiometry terms for the power of Electromagnetic radiation at a surface per unit

History

The Voigtländer Zoomar, 36–82 mm f/2. 8

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. An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum Magnification is the process of enlarging something only in appearance not in physical size The Royal Society of London for the Improvement of Natural Knowledge, known simply as The Royal Society, is a Learned society for science that was founded in 1660 Year 1834 ( MDCCCXXXIV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian Calendar (or a Common Early patents for telephoto lenses also included movable lens elements which could be adjusted to change the overall focal length of the lens. A patent is a set of Exclusive rights granted by a State to an inventor or his assignee for a fixed period of time in exchange for a disclosure of an Lenses such as these are now called varifocal lenses, in that as the focal length is changed, the position of the focal plane also moves, requiring readjustment of the focusing of the lens after each change.

The first true zoom lens, which retained near-sharp focus while the effective focal length of the lens assembly was changed, was patented in 1902 by Clile C. Year 1902 ( MCMII) was a Common year starting on Wednesday (link will display calendar of the Gregorian calendar (or a Common year starting Allen (U.S. Patent 696,788 ). The first industrial production was the Bell and Howell Cooke "Varo" 40–120 mm lens for 35mm movie cameras introduced in 1932. Böwe Bell & Howell is a US -based former Manufacturer of Motion picture machinery Year 1932 ( MCMXXXII) was a Leap year starting on Friday of the Gregorian calendar. The most impressive TV Zoom lens was the VAROTAL III from Rank Taylor Hobson from UK built in 1953. The Kilfitt 36–82 mm/2. 8 Zoomar introduced in 1959 was the first zoom lens in regular production for still 35mm photography. The year 1959 ( MCMLIX) was a Common year starting on Thursday (link will display full calendar of the Gregorian calendar. 35 mm film is the basic Film gauge most commonly used for both still Photography and Motion pictures, and remains relatively unchanged since its

Since then, advances in optical design, particularly the use of computers for optical ray tracing, has made the design and construction of zoom lenses much easier, and they are now used widely in professional and amateur photography. A computer is a Machine that manipulates data according to a list of instructions. In physics ray tracing is a method for calculating the path of Waves or Particles through a system with regions of varying propagation Velocity, absorption

Design

A simple zoom lens system

There are many possible designs for zoom lenses, the most complex ones having upwards of thirty individual lens elements, and multiple moving parts. Most however follow the same basic design. Generally they consist of a number of individual lenses that may be either fixed, or slide axially along the body of the lens. As the magnification of a zoom lens changes, it is necessary to compensate for any movement of the focal plane to keep the focussed image sharp. This compensation may be done by mechanical means (moving the complete lens assembly as the magnification of the lens changes), or optically (arranging the position focal plane to vary as little as possible as the lens is zoomed).

A simple scheme for a zoom lens divides the assembly into two parts: a focussing lens similar to a standard, fixed-focal-length photographic lens, preceded by an afocal zoom system, an arrangement of fixed and movable lens elements that does not focus the light, but alters the size of a beam of light travelling through it, and thus the overall magnification of the lens system.

Movement of lenses in an afocal zoom system

In this simple optically compensated zoom lens, the afocal system consists of two positive (converging) lenses of equal focal length (lenses L₁ and L₃) with a negative (diverging) lens (L₂) between them, with an absolute focal length less than half that of the positive lenses. Lens L₃ is fixed, but lenses L₁ and L₂ can be moved axially, and do so in a fixed, non-linear relationship. This movement is usually performed by a complex arrangement of gears and cams in the lens housing, although some modern zoom lenses use computer-controlled servos to perform this positioning.

As the negative lens L₂ moves from the front to the back of the lens, the lens L₁ moves forward and then backward in a parabolic arc. In doing so, the overall angular magnification of the system varies, changing the effective focal length of the complete zoom lens. At each of the three points shown, the three-lens system is afocal (neither diverging or converging the light), and so 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 very small (~±0. 01 mm in a well-designed lens) and so this slight defocussing is not apparent.

Simplified zoom lens in operation

An important issue in zoom lens design is the correction of optical aberrations (such as chromatic aberration, and in particular, field curvature) across the whole operating range of the lens; this is considerably harder in a zoom lens than a fixed lens, which need only correct the aberrations for one focal length. In Optics, chromatic aberration is caused by a lens having a different Refractive index for different Wavelengths of Light Aberrations are departures of the performance of an optical system from the predictions of Paraxial optics. This problem was a major reason for the slow uptake of zoom lenses, with early designs being considerably inferior to contemporary fixed lenses, and usable only with a narrow range of f-numbers. Modern optical design techniques have enabled the construction of zoom lenses with good aberration correction over widely variable focal lengths and apertures.

Whereas lenses used in cinematography and video applications are required to maintain focus as the focal length is changed, there is no such requirement for still photography, or if a zoom lens is used as a projection lens. Since it is harder to construct a lens that does not change focus with the same image quality as one that does, the latter applications often have lenses that require refocussing once the focal length has changed (and thus strictly speaking are varifocal lenses, not zoom lenses). A varifocal lens is a Camera lens with variable Focal length in which focus changes as focal length (and Magnification) changes as compared As most still cameras are autofocus these days, it hardly presents a problem. Autofocus (or AF) is a feature of some Optical systems that allows them to obtain (and in some systems to also continuously maintain correct focus on a

Designers of zoom lenses with large zoom ratios often will trade one or more aberrations for higher image sharpness. For example, a greater degree of barrel distortion is tolerated in lenses that span the focal length range from wide angle to telephoto with a focal ratio of 10x or more than would be acceptable in a fixed focal length lens or a zoom lens with a lower ratio. Although modern design methods have been continually reducing this problem, barrel distortion of greater than one percent is common in these types of lenses. Another price paid is that at the extreme telephoto setting of the lens, the effective focal length changes significantly as the lens is focussed on nearer and nearer objects. The apparent focal length can more than halve as the lens is focussed from infinity to a few feet. To a lesser degree, this effect is also seen in fixed focal length lenses that move internal lens elements, rather than the entire lens, to effect changes in focal length.

Varifocal lens

Many so-called "zoom" lenses, particularly in the case of fixed lens cameras, are actually varifocal lenses, which gives lens designers more flexibility in optical design trade-offs (focal length range, maximum aperture, size, weight, cost) than true parfocal zoom, and which is practical because of auto-focus, and because the camera processor can automatically adjust the lens to keep it in focus while changing focal length ("zooming") making operation essentially the same as a true parfocal zoom. A varifocal lens is a Camera lens with variable Focal length in which focus changes as focal length (and Magnification) changes as compared ^[2]

See also

By focal length:

• Telephoto lens
• Prime lens
• Wide-angle lens
• Superzoom

Focus attributes:

• Parfocal lens
• Varifocal lens

By system:

• List of Canon EF lenses

References

• Kingslake, R. (1960), "The development of the zoom lens". Journal of the SMPTE 69, 534
• Clark, A. D. (1973), Zoom Lenses, Monographs on Applied Optics No. 7. Adam Hildger (London).
• Malacara, Daniel and Malacara, Zacarias (1994), Handbook of Lens Design. Marcel Dekker, Inc. ISBN 0-8247-9225-4
• "What is Inside a Zoom Lens?", Adaptall-2. com.

External links

• Zoom from the Milky Way to a quark