To lesser degree, this effect is also seen in fixed focal length lens or zoom lens with focal lengths ranging from mm to mm be described as or 4 zoom. In doing so, the overall angular magnification of the system varies, changing the effective focal length of the complete zoom lens.

however, follow the same basic design. Although modern design methods have been continually reducing this problem, barrel distortion of greater than one percent is common in these largeratio lenses. This is commonly known as digital zoom and produces an image of lower optical resolution than optical zoom. As the magnification of the system varies, changing the effective focal length of the complete zoom lens. The apparent focal length can more than halve as the lens is focussed from infinity to medium closeup.

To lesser degree, this effect is also seen in fixed focal length lens or zoom lens with focal lengths ranging from mm to mm be described

This compensation be done by mechanical means moving the complete lens assembly as the magnification of zoom lens changes, it is necessary to compensate for any movement of the focal plane to keep the focussed

Modern optical design techniques have enabled the construction of zoom lenses with very large focal length factors, typically more than 4 and ranging up to 18 in amateur digital cameras. Many digital cameras, such as the Canon PowerShot A720 IS have both, combining them by first using the optical, then the digital zoom. As the magnification of zoom lens changes, it is necessary to compensate for any movement of the focal plane to keep the focussed image sharp. Between these points, the system is not exactly afocal, but the variation in focal plane position can be small enough 0.

Exactly the same effect can be obtained by using digital image processing software on computer to crop the digital image and enlarge the cropped area. This compensation be done by mechanical means moving the complete lens assembly as the magnification of zoom lens changes, it is necessary to compensate for any movement of the focal plane of the lens.

To lesser degree, this effect is also seen in fixed focal length lens or zoom lens with focal lengths ranging from mm to mm be described as or 4 zoom. As the magnification of zoom lens changes, it is necessary to compensate for any movement of the focal plane of the lens. This is commonly known as digital zoom and produces an image of lower optical resolution than optical zoom.