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How to Buy SLR Lenses

One of the best things about a digital SLR is its versatility. Because the camera uses interchangeable lenses, you can literally choose the lens you'd like to suit the photographic occasion. What's more, DSLR lenses produce far sharper results than built-in lenses on point-and-shoot cameras. Consumer Reports

Getting started - SLR lens guide
Digital SLR lenses typically are quicker to focus and come with a variety of creative features, including built-in optical image stabilization for steadying shaky shots and wide apertures for shooting in low light. The problem is that many of the best lenses are expensive—not to mention so big and heavy that you wouldn't want to carry one around all day. This SLR lens guide can help take some of the confusion out of shopping.

How lenses on a DSLR work
An interchangeable lens is attached to a digital SLR via a locking mechanism called a "mount." Once it's mounted, the lens provides you with a specific "focal length." (Technically, that focal length is the distance between the lens' glass elements and the camera's sensor, which captures the image). The greater a lens' focal length, the closer it brings the subject you are shooting. A given lens is usually designed to work with just a single brand of camera. For example, a Nikon lens will fit a Nikon DSLR, but not a Canon. See the Brands section for more information.

A lens is like a tube filled with glass lenses that funnel light onto a digital sensor. The physical size of the lens, and the amount and shape of the glass will affect its focal length. A standard or "normal" lens, with a fixed focal length of 50 mm, has a horizontal angle of view that is about the same as what the human eye perceives. A longer lens, such as a telephoto, will bring you closer to your subject while a shorter, rounder, wide-angle lens will give you a broader perspective.

Some lenses, called zooms, provide a range of focal lengths that you can control as you shoot. Some of the most typical zoom lenses used with consumer DSLRs range from 18 to 55 mm to 24 to 85 mm. For shooting subjects at greater distances, there are telephoto zoom lenses, with ranges such as 70 to 200 mm.

For shooting landscapes or other wide subjects, there are wide-angle zooms, with a range such as 12 to 24 mm. For the greatest versatility, there are ultra zooms, with ranges as great as 28 to 135 mm or 18 to 200 mm. Because the image sensors on digital cameras are usually smaller than a frame of traditional 35-mm film, when a lens is used with a DSRL, you need to account for that difference by figuring its effective focal length. For example, a 50-mm lens on a Canon Digital Rebel would have an effective (or "equivalent") focal length of 80-mm lens when taking into account the camera's 1.6x magnification. Such magnification factors vary from one brand of camera to another, and sometimes even among models within the same brand.

Some higher-end digital SLRs use so-called "full-frame" sensors, which are about equal in size to a frame of 35-mm film. With such cameras, there is no lens magnification, or equivalent focal length. In short, a 50-mm lens remains a 50-mm lens on a full-frame sensor SLR such as the Canon 5D Mark II or Nikon D700.

Kit lens vs. interchangeable lens
If you just purchased a digital SLR, you might be wondering why you'd need to buy a lens if your camera came with one. It's true that most consumer digital SLRs are sold with a "kit" lens—typically a short standard zoom with a focal range of around 18 to 55 mm (28-to-85-mm digital equivalent)—which is cost effective, but not necessarily of the highest quality.

The problem with such lenses is that they limit what you can do with them creatively because they're usually not long enough to reach distant subjects such as wildlife and they're not wide enough to capture a broad perspective such as when photographing landscapes. Kit lenses are also not ideal for portraits because their focal lengths are shorter than what's preferred for portraits and their apertures aren't suited for blurring the background, which helps to draw attention to the person you're shooting. Kit lenses aren't as rugged or as sharp as more-advanced lenses because they're typically made of plastic rather than metal and glass. To see how some inexpensive "kit" style lenses compare with expensive ones, see our Ratings [link to lens ratings] of SLR lenses (for subscribers).

Even if you can afford one, a higher-priced, higher-quality lens might not always be your best choice. The most important consideration in choosing a lens is that its aperture, focal length, and other features match the type of shooting you intend to do.

For a good-quality standard zoom lens, expect to pay at least $300. If you want one with a wider aperture—i.e. a smaller f/stop number such as f/2.8, which lets in more light—you could pay two to three times that.
A quality wide-angle or telephoto zoom lens can range from expensive to extremely expensive, so expect to pay at least $600 for a decent wide or long zoom. Any lens with an aperture of f/2.8 or faster sells for $1,000 or more.

Because they don't offer the versatility of a zoom, fixed focal length lenses are much less expensive even when they offer a fast aperture well suited for taking portraits. Most point-and-shoot cameras can't replicate this effect because their sensors are very small—the bigger the sensor, the shallower the depth of field. A 50-mm lens with an f/1.4 aperture will sell for about $300. A 50-mm lens with an f/1.8 aperture sells for less than $100.
In addition to costing less than a zoom, a fixed-focal-length lens is usually sharper and brighter, with better contrast, and suffers from fewer defects, mainly because it's made with fewer glass elements.

Types of SLR lenses
Before you shop, take stock of the type of photography you plan to do. If you photograph a lot of wildlife, your needs will differ from someone who likes to shoot mainly portraits. Here's a rundown of the different types of lenses you'll see when in the store.

Standard zoom lens
All-purpose lens with a typical range of 18 to 55 mm.
Fixed focal length "prime" lens
This lens is less versatile than a zoom but usually has better optical quality and a smaller, lighter build.

Telephoto zoom lens
Designed to get close to the action, for sports or nature. A popular telephoto zoom lens is 70 to 200 mm or higher.

Wide-angle zoom lens
Best for capturing landscapes or groups of people, with a typical focal range of 16 to 35 mm.

Macro lens
For photographing extreme close-ups of small objects such as insects and plant life. 50 mm and 100 mm are popular focal lengths for Macro lenses.

Specialty lenses
For capturing images with special looks for artistic purposes. Ultra-wide-angle "fish-eye" lenses are popular, as are "Lensbaby" selective-focus lenses that let you move the optics to produce creative effects.

Tilt and shift lenses
These lenses provide perspective control in architectural and product photography.

Soft-focus lenses
Use these for portrait and beauty photography.

SLR lens features
Before you venture into a camera store, it's a good idea to learn the lingo so that you can get the SLR lens features you need. If you have a friend who is a photography buff, you might want to experiment with her camera and lens before making an investment of your own.

Fast apertures
The aperture is the hole, or opening, in the lens that determines how much light is let through to the imaging sensor. The widest opening a lens is capable of determines its maximum aperture. Most professionals who shoot portraits, sports, or anything in low light without a flash are drawn to "fast," or

wide, aperture lenses.
A wider aperture in a lens (a larger hole) is signified by a smaller f/stop number such as f/2.8 or f/1.4. A higher f/stop number, such as f/16 or f/22, produces a tiny hole or aperture. The reason they're known as "fast" apertures is that the wider the opening, the more light that can reach the sensor, allowing photographers to shoot at a faster shutter speed to freeze action and get non-blurry images even in low light.
For portrait photographers, a wider aperture creates a shallower depth-of-field, which means that only a small amount of the scene in the foreground is in focus. When taking pictures of people, this shallow depth-of-field is a good thing because it helps to draw attention to a face. When you set a lens to its widest aperture, you lose some sharpness. How much you lose depends on the quality of the lens.

If you're looking for a lens with a wide aperture-say, f/2.8-you'll notice that it's quite a bit more expensive than one with a smaller maximum aperture-f/3.5 or 3.8, for example. That's because those wider apertures require larger diameter lens elements, which makes them heavier and more expensive.

Image stabilization
When using a lens with built-in image stabilization, you can shoot at a few shutter speeds slower than you would otherwise and still achieve a blur-free image. Though image stabilization can add considerable cost to a lens, we recommend it for most telephoto lenses because it will help keep your shots blur free. But bear in mind that an image stabilizer will make a lens darker. With better lenses, the benefits of stabilization outweigh the loss of light. With other lenses, they might not.

If you're shopping for a lens, you're likely to see the term listed as Image Stabilization (IS), Vibration Reduction (VR), or Vibration Compensation (VR), depending on the lens manufacturer. Lenses with built-in image stabilization are able to physically shift a glass element in the lens to compensate for shaky hands to reduce image blur. This is done in slightly different ways depending on the manufacturer, but typically involves a small gyroscopic sensor embedded in the lens that automatically detects hand movement and then adjusts the glass to keep the shot steady.

An alternative to image stabilized lenses is in-camera image stabilization, which automatically shifts the imaging sensor to compensate for handshake. Companies that employ sensor-based image stabilization in their cameras include Olympus, Sony, and Pentax. The effectiveness of sensor-based stabilization varies with the focal length of the lens. The longer the lens' focal length, the less effective the stabilization.

Digital specific lenses
Some manufacturers sell what are known as "digital specific" or "digital lenses" that are designed to work better with the sensor in digital SLRs as opposed to traditional lenses that are optimized for film. There's some debate as to whether there's a real advantage to digital lenses in terms of image quality but one thing can be said for certain-they're smaller and lighter than traditional lenses. Digital lenses take advantage of the 1.3x2.0 smaller size caused by image sensors, giving you better focal range in a smaller package. Many digital lenses are also less expensive than traditional lenses because their smaller diameter means that they require less glass.

Digital lenses also provide better corner-to-corner sharpness in your photos because they're directly calibrated to the camera sensor, to direct the light on the edges of the sensor at an angle less steep than would be the case with film. Olympus was the pioneer in creating digital lenses but now most of the major manufacturers have a line of lenses designed specifically for digital sensors.

Digital lenses are made for digital cameras with smaller, APS-C, Four Thirds, or Micro Four Thirds sensor formats and will not function properly on DSLRs that use full-frame sensors, which require a larger diameter of the lens, causing corners of the image to be blocked out (this is called vignetting). They also will not work on some digital and film cameras. Micro Four Thirds is a new system created by Panasonic and Olympus to help produce smaller cameras. The system is slightly different from SLRs because it does not use mirror or pentaprism viewfinders on top of the camera--just an electronic shutter--which allows Micro Four Thirds models to be smaller.

Zoom vs. prime lenses
Zoom lenses that let you take photos across a wide focal range such as 28 to 135mm are fairly typical. This gives you a lot of versatility when you shoot. On the down side, zoom lenses are usually more expensive than fixed focal length or "prime" lenses. They're also heavier.
While there's a definite appeal to being able to get closer to or farther back from your subject by just turning the zoom ring, you might also want to consider a place in your camera bag for a prime lens. As mentioned before in this guide, you can get a nice and light 50-mm f/1.8 lens for less than $100. Prime lenses also have a reputation for being better quality than zoom lenses and for producing sharper images. (This, of course, depends on which prime and which zoom lens you are comparing.)

Ultra zooms
Ultra zooms offer an extremely wide focal range of, for example, 18 to 200mm. This type of ultra zoom lens is great for vacations because it allows you to travel with just one lens to use under every shooting condition. Best of all is that ultra zooms are relatively inexpensive, selling for from $500 to 600 with built-in image stabilization.

There are some drawbacks to these light and economical lenses though. And when stacked up against images from a good prime lens, images captured with an ultra zoom typically don't look as crisp. Ultra zooms are also built mostly of plastic and so are less rugged and weather resistant.

Build quality
The build quality of a lens is an important thing to consider if you plan to take photos in less than optimal conditions. High-end lenses are made of metal rather than plastic or polycarbonate, so there's some protection if you drop or bump them. The actual lens mount on a higher-priced lens is almost always made of metal while some cheaper lenses use a less sturdy plastic lens mount. They're also weatherized to prevent moisture from seeping in and resistant to dust and dirt. Some photographers also like the heavier weight of a high-quality rugged lens because it's easier to keep steady when you shoot. Most important: More-expensive lenses use better glass.

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