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Telephoto Zooms
Like fixed-focal-length lenses, tele-zooms come in a wide variety of price ranges. You can get an entry-level model for less than $200 or pay more than $5,000 for a top pro optic. The high-end pro lenses offer many benefits over entry-level lenses, including faster maximum apertures, better image quality, faster autofocus performance, better materials and more-rugged construction—after all, that's why they cost so much. If you're on a tight budget, the major-brand, entry-level telephoto zooms deliver good image quality and let you get started in telephoto photography. But remember that it's the lens that makes the picture. The best pro camera body with a mediocre lens can't deliver better than mediocre image quality, while an entry-level SLR with a good lens can turn out very good image quality, even if it won't shoot 8 fps or withstand the elements like a pro model.
The following are key considerations when choosing a telephoto zoom lens.
One Ring Or Two?
Some zoom lenses have two control rings—one for focusing and one for zooming. Others use a single ring: rotating it focuses the lens and pushing/pulling it zooms the lens. With the one-ring method, you won't accidentally zoom when you intend to focus, but many photographers are more comfortable with the twin-ring system. Before you buy a tele-zoom, try out the focusing and zoom controls to see how you like the configuration.
Class Glass
If you shoot a lot at wide apertures, you'll probably want a lens that corrects the aberrations that are especially evident at wide apertures. Low-dispersion elements, with such designations as ED, LD, UD, ELD, SLD and SED, correct chromatic aberrations to improve sharpness and contrast as do fluorite elements. Aspherical elements correct spherical aberrations, improving sharpness. The Canon EF 70-300mm ƒ/4-5.6 DO IS USM zoom features multilayer diffractive optics (the "DO" in the name), which cancel out chromatic aberrations produced by conventional optics and correct spherical aberrations as well, improving image quality and allowing for much more compact lenses.
Focusing Considerations
Many lenses employ front focusing, where the front element rotates and moves away from the camera body as you focus from infinity toward the minimum focusing distance. This makes using orientation-sensitive lens attachments such as polarizers and graduated filters difficult. Lenses that employ internal or rear focusing don't rotate the front element, so filters will retain their orientation during focusing. And since these lenses' physical length doesn't change during focusing, there's also less weight shift. Another advantage is that moving only small internal elements instead of the large front ones makes for quicker and more accurate autofocusing.
Some AF lenses permit you to focus manually without leaving AF mode (the Canon USM lenses that have focusing scales and the Nikon AF-S Silent Wave lenses, for example); others provide quick switching from autofocus to manual focus mode (Pentax's Quick- Shift Focus and Tamron's MF/AF Switchover, for example). This can be a real time- and shot-saver.
Many long lenses provide a focusing range limiter. You can set this for full travel (allowing the lens to focus from infinity to its closest focusing distance) or for limited travel (allowing the lens to focus from infinity to about twice its minimum focusing distance or from twice its minimum focusing distance to its minimum focusing distance). By using the range limiter, you'll get much quicker autofocusing performance because the lens won't have to "hunt" through such a great distance range.
"Macro" Capability
Many zoom lenses have the word "macro" in their name. Don't confuse these with true macro lenses, which focus down to 1:1 (life-size) magnification. Macro zooms will focus closer than standard zooms of equivalent focal-length range, but often no closer than a 1:4 reproduction ratio (1/4 life-size). Sigma and Tamron offer 70-300mm zooms that are an exception, focusing close enough to produce a 1:2 (1/2 life-size) reproduction ratio.
Even if you're not interested in true macro shooting, consider the minimum focusing distance when comparing potential lens purchases. If you like to photograph flowers and other small subjects, a 70-300mm zoom that focuses down to 3.1 feet at 300mm will make you a lot happier than one that focuses down to only 4.6 feet or down to 3.1 feet but only at the 70mm setting.
Lens Stabilization
Long lenses magnify the effect of camera shake, so it's best to mount them on tripods. If you prefer to work handheld, you might consider a lens that has a built-in image stabilizer. Stabilizers compensate for camera shake, allowing you to get sharp images handheld at two or three shutter speeds slower than is possible without a stabilizer. The Canon Image Stabilization lenses are identified by "IS" in the designation and currently include the EF 70-200mm ƒ/2.8L IS USM, EF 70-300mm ƒ/4-5.6 IS USM, EF 70- 300mm ƒ/4.5-5.6 DO IS USM and EF 100-400mm ƒ/4.5- 5.6L IS USM tele-zooms. Nikon offers the 70-200mm ƒ/2.8G ED-IF AF-S VR Zoom-Nikkor, "VR" standing for "Vibration Reduction." Sigma's entry is the APO 80-400mm ƒ/4.5- 5.6 EX OS (for Optical Stabilizer) zoom.
Tripod Mount
When the lens weighs more than the camera body, it's best to mount the lens rather than the camera on the tripod for balance and to save stress on the lens mount. Many telephoto lenses, zoom or fixed-focal length, come with tripod mounts. The best mounts allow you to switch between horizontal- and vertical-format shooting without adjusting the tripod; just loosen the knob and rotate the camera/lens combo in the mounting ring. The mounting ring makes a great left-hand grip for handheld shooting, too.
Zoom Lock
One annoyance with heavy zoom lenses is that they tend to extend as you carry them, thanks to gravity. Some lenses have a zoom lock, which can be used to lock the lens at its shortest length for easier oncamera carrying.
Fixed Vs. Variable Maximum Aperture
As with fixed-focal-length lenses, faster maximum apertures let you shoot in dimmer light, or at faster shutter speeds. They also provide faster autofocusing performance and easier manual focusing. If you do a lot of low-light or handheld shooting, you'll want a fast lens, but keep in mind that fast lenses cost a lot more than slower glass.
A consideration unique to zoom lenses is variable maximum apertures. Constant-aperture zoom lenses have a fixed maximum aperture: if you set, say, a 70-200mm ƒ/2.8 zoom to ƒ/2.8, it stays at ƒ/2.8 at all focal lengths. Most lower-cost zooms have variable maximum apertures: if you set a 70- 210mm ƒ/4-5.6 zoom to ƒ/4 at the 70mm setting and zoom to its longest focal length, the aperture will change to ƒ/5.6. TTL metering automatically compensates for this, but if you're using a handheld meter, you'll have to take it into consideration. Constant-aperture zooms also maintain focus when zoomed; variable-aperture zooms must be refocused when you change focal lengths. Autofocusing systems automatically handle that, but when focusing manually with a variable-aperture zoom, be sure to focus at the focal length you're going to use for the shot.
Digital-Only Zooms
Because the image sensors in many D-SLRs are considerably smaller than a full 35mm film frame, a lens designed specifically for them doesn't have to project as large an image circle. Thus, lenses specially designed for such cameras can be smaller and more efficient on these cameras than lenses designed for 35mm SLRs. The drawback is that these "APS-C"-class lenses (so named because these image sensors are about the size of an Advanced Photo System C-format image frame) can't be used on full-frame cameras, in part because vignetting will occur. Lens manufacturers identify these lenses via code letters in the lens name: Canon designates its "APS-C" zooms "EFS"; Nikon labels its "DX"; Pentax, "DA"; Sigma, "DC"; and Tamron, "Di II." All lenses for Olympus' Four Thirds System D-SLRs are digital-only; they use a different mount than the company's old OMsystem film cameras. Sigma and Tamron also make lenses designated "DG" and "Di," respectively; these are optimized for digital SLRs, but provide a standard 35mmformat image circle and so can be used with all SLRs, film and digital, for which a mount is available.
What's Best For You?
The best telephoto zoom lens for you depends on your shooting needs. If you bought an entry-level D-SLR with an 18-55mm standard zoom, one of the 55-200mm zooms is a logical next step. If you like to photograph birds and other wildlife, or sports-action, a longer lens is a better choice: 300mm and up. If you prefer wide-angle work, you don't need a tele-zoom.
A good plan is first to decide what focallength range is most useful to you and the kind of photography you do. Then check out what's available in that focal-length range. The accompanying chart, while not complete, offers a good idea of what's out there. Consider the features we've discussed and how each might help your photography.
If you can afford it, get one of the pro zooms. They're faster, perform better and last longer. But even an entry-level, major-brand tele-zoom lets you get shots you can't get with shorter focal lengths and provides a great way to break into telephoto photography.
(mm)
Groups
(special elements)
(ft.)/Magnif.
(in.)
(oz.)
(4 UD)
(2 UD)
(2 ED)
(5 ED)
(ED, Asp)
(MF)
(ELD, SLD)
(LD)
(MF)
(MF)
(1 ED)
(Asp)
(1 SLD)
(3 SLD)
(4 SLD)
(3 SLD)
(1 LD)
(LD)
(MF)
(MF)
(1 UD)
(3 ED)
(4ED)
(3 SLD)
(1 SLD)
(T-mount)
(1 Asp)
(MF)
(4 SLD)
(3 SLD, Asp)
(2 ELD)
(IF)
(2 LD)
(4 ED, 1 SED)
(3 ED)
(3 ED)
(SLD)