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 (VC), 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.

See also:

Digital picture frames

Scanners

Printers

Cell phones