There's a convenience factor in using a zoom lens. If you're on a hike and out shooting for a long day, the last thing you want to do is carry a bunch of lenses. They can add a lot of weight to your bag and take up limited real estate that could otherwise be reserved for useful gadgets and tools.
There's a quality advantage, too. It used to be that a zoom lens' true asset was simplicity. The range of focal lengths that were offered in older zooms was useful, but unfortunately, the high quality and sharpness that fixed or prime lenses provide wasn't matched. This isn't the case today. Optics technology, lighter materials and advanced designs have brought the quality and convenience factors together.
When choosing a zoom lens, first consider what you'll be shooting. One lens may suit all of your photographic needs, so you can end up saving some money as well as free yourself from the burden of extra gear.
Wide-angle zoom lenses are perfect for showing the expanse of a landscape or placing flowers or rocks in your foreground with a huge sky as a backdrop. Newer wide-angle zooms have become even wider due to the advent of small digital-format D-SLRs—your D-SLR with a full-sized 35mm sensor will provide an even wider angle of view. The standard wide-angle zoom is in the 16-35mm range, but small-format digital lenses equal that angle of view with a 10-22mm range.
Mid-range wide-to-telephoto lenses have become popular due to their resourcefulness. The wide focal length can capture the span of an area and is useful if you have to shoot in tight spaces, while the telephoto end provides you with a portrait lens, which is ideal for isolating foliage or flowers. I've seen a lot of photographers stick with just this one lens because it offers them all the focal lengths they need. Mid-range wide-to-telephoto lenses commonly have focal lengths of approximately 28-80mm or 100mm. Small-format lenses offer the equivalent in focal lengths of about 18-55mm.
Extreme-range wide-to-telephoto zooms are relatively new. These lenses typically go from 28-300mm (18-200mm in small-format digital). They offer a very large range, although size and lens speed can be compromised.
A standard mid-range telephoto zoom lens is effective not only for landscapes and macro photography, but for hiking as well. Mid-range zooms give you enough of a zoom to magnify and compress your scene, but they're small and light enough to carry and place on a light tripod without dragging it down. Standard mid-range telephoto focal lengths typically are 70mm to 210-300mm.
If you plan on photographing wildlife, you'll need a telephoto zoom. Focal lengths of these lenses range from at least 100-400mm or 200-400mm. They afford you the ability to photograph animals at a distance without disturbing them in their natural habitat. Telephoto zooms are heavy lenses, as they incorporate a lot of glass to achieve their focal length, so you'll likely need a tripod.
You may be shooting images in low light, requiring a lens with a large maximum ƒ-stop. A fast ƒ/2.8 lens is ideal for photographing subjects in dimly lit situations like dusk or dawn, or any other low-light setting where you don't want to use a flash. A lot of photojournalists need a lens with a large maximum ƒ-stop because it allows them to handhold their camera, which is an asset when street shooting. This also can apply to wilderness shooting where trees can limit light. Especially with long zoom ranges, you should notice if a zoom lens' maximum aperture changes. A variable-aperture lens has different maximum apertures at different focal lengths. So when you zoom out, the aperture changes to a smaller one and, consequently, the shutter speed has to slow down to achieve the correct exposure. For example, a 28-200mm lens might be ƒ/3.5 at 28mm, but ƒ/5.6 at 200mm. This may not matter to you if you're using a tripod, but it's something to consider if you're handholding your camera.
When standard optical glass is used in telephoto zoom lenses, chromatic aberration can occur. Also referred to as color fringing, chromatic aberration is the inherent tendency for glass to disperse a ray of light into the colors of the rainbow. This effect usually is visible where the lighter parts of your scene meet the darker parts, such as tree branches against a bright sky.
These aberrations or color fringes can be especially noticeable if you blow up your picture beyond 8x10 inches. To eliminate chromatic aberration, many manufacturers employ special glass in their lenses to correct for it. Low-dispersion (LD), extra-low-dispersion (ELD) and special low-dispersion (SLD) glass and apochromatic lenses (APO) help to refocus the dispersing light waves together so they meet at the same point instead of separating out. Without lenses like these built in to the design, quality can suffer.
Aspheric elements also help to limit aberrations by refocusing light waves at the edge of the lens to the same distance as light waves that enter through the center of the lens. Spherical lenses can't do this because of their pronounced curvature, and color aberrations can occur in your image. Lenses that incorporate two aspheric elements will correct for the blue and red waves, while three aspheric elements will additionally correct for the green. When aspheric elements work in conjunction with the other special glass elements mentioned, increased correction for various types of aberrations are made.
Newer optics called diffractive optical (DO) elements use a special optical construction to reduce the size and weight of the lens while maintaining high optical quality.
Several manufacturers have included multi-coatings on their lenses. Usually, there are seven or eight coatings layered on the optics to help reduce reflections that cause flare. When flare is limited, contrast and color saturation are increased in your image. Digital SLR sensors have a shiny surface that reflects more light than film. Because this surface increases the chance of flare occurring, improved multi-coating becomes essential in digital shooting.
Although each manufacturer's coating is different and made from various materials, you can be assured that tests have been done to prove the reduction or elimination of flare and ghosting.
Many lenses today have an internal focusing (IF) mechanism, which offers great advantages. An IF mechanism moves elements inside the lens to focus without extending the barrel of the lens. This makes for more compact and lighter construction, which is especially useful if you're carrying a telephoto on a trek. Additionally, by keeping the barrel from extending during focusing, better balance of your camera is achieved, whether you're using a tripod or handholding your camera. IF also keeps the front end of your lens from rotating so your filters stay in place.
If you're shooting in a low-light situation, consider a long zoom lens with lens stabilization. Also known as Image Stabilizer (IS) by Canon, Vibration Reduction (VR) by Nikon or Optical Stabilizer (OS) by Sigma, this function automatically corrects for camera shaking that can cause blur. If you plan on handholding a long lens, using a slow shutter speed, or if you have a lightweight tripod that isn't strong enough for a heavy lens, this mechanism can equal a two- to three-stop difference and produce a sharp image that would otherwise turn out blurry due to unsteady support.
Size And Weight
New materials and optical innovations have allowed for smaller and lighter lenses to be made. Lens designers are working to continually reduce the size of their lenses and still retain quality. Lenses specifically created for smaller-sized digital SLR sensors are particularly compact and lightweight. So, if you want to save your back and shoulders from the distress that a heavy pack can cause, lighten your load. Carry less by carrying more zooms!
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