How to use Zoom Lenses

How to Use Zoom Lenses

  • Zoom lenses are lenses with variable focal length. A zoom lens is designed in such a way that one or more of its glass elements can be moved with respect to one another, so that its focal length can be continuously changed throughout a fairly wide range. The usual ranges are from somewhat wide angle to somewhat telephoto, from very short to moderate wide angle, from moderate wide angle to normal, or from a short to a longer telephoto. This can be a great convenience when the photographic situation is changing so rapidly that there is little or no time for changing lenses.

  • Zoom lenses can be divided for convenience into four general categories. The most versatile in some ways are those that combine wide angle, normal, and telephoto focal lengths, such as a 35-105 mm lens. Next handiest are the short to longer telephoto zooms, typified by a 70-205 mm range. Less often seen, but sometimes very useful, are those that feature focal lengths that range from wide angle to normal, such as 24-50 mm lens. There is also the macro zoom lens, typically a short to longer telephoto lens with a close focusing capacity.

  • Zoom lenses can generally be used much like other lenses, but they give you the unique capability of infinitely adjustable image size, within their individual zoom and focusing range. This is useful in any form of photography, but is especially so in color slide work, where you cannot adjust the image size or composition, after the fact, in the darkroom.

  • Additionally, zoom lenses offer a further unique capability: you can change the lens focal length, and hence the image magnification, over the period of a time exposure, thus radially smearing the image.
    Zoom lenses often pose certain characteristic problems. They are frequently subject to substantial internal reflections that tend to introduce "flare" (a lowering of image contrast), and if the lens is pointed toward, or nearly toward, a light source such as the sun, this will possibly cause single or multiple bright spots or pseudo images on the film for film photography. Flare is significantly reduced and often eliminated by closing the lens diaphragm one or more f-stops from maximum. Actual bright spots from light sources must be watched for any time you are working into the light. It is sometimes possible to use them as creative image elements if you see them and integrate them into your composition. But if you fail to notice them while composing, they may well spoil your picture.

  • In times past, no zoom lens could offer as much image resolution (picture sharpness) as a fixed focal length lens of comparable focal length. Currently, however, with advances in lens design and especially the widespread introduction of computer designing coupled with the use of special rare earth glasses, the general quality of zoom lenses have greatly improved.

  • The best new designs are very good indeed, and they offer a degree of operational flexibility and versatility unmatched by more conventional equipment.

  • In compact photography, zoom lenses are the most commonly seen. Although fixed focal length lenses are still providing better quality in most cases but it has become limited to special uses.

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