Zoom lenses

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The versatility and convenience that zoom lenses offer are major reasons why prime lenses fell out of favor with the masses. Savvy photographers still prefer primes but acknowledge the benefit of zooms. Zoom lenses offer a variable range of focal lengths within a single lens, allowing you the equivalent of having three, four, or more single-focal-length lenses in one lens. Zoom lenses are available in wide-angle and telephoto ranges.

In a zoom lens, part of the lens system moves along the optical axis to change the focal length while another part moves simultaneously to compensate for the resulting shift in focus. As a result, zoom lenses must have at least two lens groups that can move along the optical axis. The first group at the end of the lens compensates for focus shift and is referred to as a compensator. The second group is moved to change the focal length and is referred to as a variator. This group achieves focus by adjusting the focal point.

For example, in a wide-angle zoom lens with two lens groups, the first group has negative refraction (divergence), and the second group has positive refraction (convergence). The lens is designed with retro-focus construction. Furthermore, to solve various limitations of this design, to keep the lens size compact, and to compensate for aberrations with fewer lens elements, most lenses use a multigroup zoom with three or more movable lens groups.

Some zoom lenses are slower than single-focal-length lenses, and getting a fast zoom lens usually comes at a higher price, usually in the L category. In addition, some zoom lenses have a variable aperture, which means that the lens's minimum aperture changes at different zoom settings.

Zoom lens advantages

The obvious advantage of a zoom lens is the ability to quickly change focal lengths and image composition without changing lenses. In addition, you need only two or three zoom lenses to encompass the focal range you use most often for everyday shooting. For example, carrying a Canon EF 16-35mm f/2.8L II USM lens and a Canon EF 70-200mm f/2.8L IS USM lens — or a similar combination of lenses — provides the focal range needed for most shooting.

Of course, a zoom lens also offers the creative freedom of changing image composition with the turn of the zoom ring — all without changing your shooting position or changing lenses. Most mid-priced and more-expensive zoom lenses offer high-quality optics that produce sharp images with excellent contrast.

6.5 A zoom lens like the very sharp EF 70-200mm f/2.8L USM lens offers a good deal of versatility both on location and in the studio. I shot this for a magazine spread featuring holiday desserts by using a lower midrange f/stop to control the bokeh of the background lights and then added a soft vignette in Lightroom. ISO 100, f/5.6, 1/15 sec.

Zoom lens disadvantages

Although zoom lenses allow you to carry around fewer lenses, they tend to be heavier than their single-focal-length counterparts. Add more weight for that fast glass, and you have a lens with some serious heft. Mid-priced fixed-aperture zoom lenses are likely to be slow, meaning that with require slower shutter speeds, which limit your the camera.

6.5 A zoom lens like the very sharp EF 70-200mm f/2.8L USM lens offers a good deal of versatility both on location and in the studio. I shot this for a magazine spread featuring holiday desserts by using a lower midrange f/stop to control the bokeh of the background lights and then added a soft vignette in Lightroom. ISO 100, f/5.6, 1/15 sec.

maximum apertures of only f/4.5 or f/5.6, they ability to get sharp images when handholding

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