How to buy a camera lens

If you purchased your digital single-lens reflex (DSLR) as part of a kit, you already have a basic lens that takes pretty good pictures. However, part of the attraction of this type of camera is that you can switch out lenses to get the best shot in any situation. From powerful zooms that get you up close to high-speed lenses that specialize in low-light settings, you have plenty of options for your second lens. While some lenses may go for more than you spent on your camera, you don’t have to pay a lot to get a great lens. The real question is: how do you find the right one for your needs?

Understanding glass

To understand what makes one lens different from another, you first need to be familiar with a few basic concepts.

Focal Length Technically speaking, a lens’s focal length, represented in millimeters, is the distance between the rear element of the lens and the focal plane, where the parallel beams of light entering a lens converge to a point. This matters to you because the focal length determines the lens’s viewing angle. The shorter the focal length, the wider the field of view, and the more of a scene your camera can capture. As you increase the focal length, the field of view narrows-so you see less of the scene-and objects appear magnified in relation to their environment.

In the world of traditional 35mm film, focal lengths ranging from 16mm to 35mm are generally considered wide-angle. A 50mm lens is referred to as “normal”-because it comes closest to covering the same field of view as the human eye-and anything over 100mm is considered telephoto. However, focal length is a bit more complicated when it comes to DSLRs. That’s because the cameras’ image sensors are smaller than 35mm film, so they crop out some of the image and give the effect of a longer focal length. To get a sense of how this discrepancy will impact the viewing angle of your lens, you have to multiply the digital camera’s crop factor-which you’ll find in its manual-by the focal length of the lens. A Nikon D40, for example, has a crop factor of 1.5X. As a result, a 35mm lens has a field of view equivalent to that of a 52mm lens when placed on the D40.

Aperture The other key component in evaluating a lens is its aperture. The aperture is one of the mechanisms that controls the amount of light that passes through the lens to the image sensor. The aperture is usually referred to in terms of f-stops, and is represented by a number such as f/2.8. The smaller the number, the larger the opening, and the more light it allows into the camera. Because it collects more light, a lens that opens to a wide aperture lets you maintain faster shutter speeds in low light-this can be essential for obtaining sharp images from a handheld camera. Wider apertures also provide more creative control by giving you the option to throw backgrounds out of focus.

The speed of a lens is described by its maximum aperture. Some lenses, for example, max out at f/4.5, while others can open all the way to f/2 or wider. If you’re looking at a zoom lens, which has a range of focal lengths, you’ll see the maximum aperture listed as a range, such as 55-200mm f/4-5.6. This lens zooms from 55mm, with a maximum aperture of f/4, to 200mm, with a maximum aperture of f/5.6. This means your camera will choose a slower shutter speed as you zoom in.

Keep in mind that faster lenses-lenses with smaller maximum apertures-are generally both heavier and more expensive than slower lenses. While you might not mind spending a bit more for a better lens, the extra weight may be less enticing.

Image Stabilization At slower shutter speeds, an imperceptible move on your part can create a blurry photo, but a lens or camera with stabilization can counteract this shaking, letting you shoot handheld shots in low light. Canon lenses with image stabilization have IS in their name, while Nikon uses the term Vibration Reduction, or VR. You’ll pay a bit more for image-stabilized lenses, but they’re generally worth it-especially if you don’t always carry a tripod. Of course, you won’t need stabilized lenses if your camera body offers image stabilization. (For more on image stabilization, see “Steady Your Shot”.)

Building your collection

The zoom lens included with many DSLR kits offers a focal length range of 18mm (equivalent to 28mm to 35mm, depending on the camera’s crop factor) to 55mm (equivalent to 80mm to 105mm). This takes you from a moderate wide-angle view to a slight telephoto. These lenses aren’t bad-they’re lightweight and take good pictures when you’re shooting outdoors in daylight or indoors with a flash. However, they tend to be slow, which means they don’t do well in low-light conditions. When you’re ready to expand, consider investing in a prime lens (which has a single focal length) or a longer zoom lens.

Prime Lenses If you’re looking to develop your compositional skills and get a better lens in the process, I recommend purchasing a prime lens with a focal length between 35mm and 85mm. Prime lenses tend to have better glass in them than comparably priced zoom lenses, and they get you out of the “zoom rut,” where you stand in one place and zoom in or out to fill your frame. With a fixed-length lens, you need to move around to get your shot, and over time that act will help you create much better compositions. Also, most prime lenses have a wider maximum aperture, which makes it easier to get sharp shots under low-light conditions.

These images show the difference a prime lens with a wide aperture can make. The image on the left was taken with Canon’s 24-85mm f/3.5-4.5 lens. Even at the lens’s maximum aperture (f/4.5) the ISO had to be raised to 3200, creating more image noise and harsher tones. The image on the right was taken with Canon’s 85mm f/1.8 prime lens. The wider aperture let in more light and allowed me to lower the ISO to 1600, reducing the image noise and more accurately capturing the scene’s lighting. (Both of images were shot at 1/60th of a second without a tripod.)

So where do you start when selecting a prime lens? All of the major camera companies offer good prime lenses from 35mm to 100mm at prices under $500. For Digital Rebel owners looking for a good starter lens, I recommend Canon’s 35mm f/2.0 and 50mm f/1.8. Both lenses offer better low-light performance than the zoom lenses that come in the kits. The 50mm f/1.8 in particular is a bargain-you can find it for under $100 at most camera stores-and is extremely light. You can also find comparable prime lenses for Nikon, Sony, Olympus, and other DSLR systems.

Zoom Lens If you want to grab action photos, a telephoto lens in the 100mm to 300mm range is your best bet. Thanks to the crop factor on DSLRs, you don’t need too much zooming power. A 200mm telephoto lens turns into a 300mm lens on a Nikon D40. Likewise, Canon’s 70-300mm f/4-5.6 IS lens-one of my all-time favorites-becomes a 112-480mm zoom on a Canon Digital Rebel XTi. But remember that, unless you’re willing to spend a lot of money for an f/2.8 telephoto lens, you’ll need to boost the ISO in many situations to get shots at reasonable shutter speeds. This is where it pays to get a lens with image stabilization.

Note About Nikon Lenses If you have one of Nikon’s entry-level DSLRs-the D40, D40x , or D60 -you should be aware that the autofocus feature on some older Nikon lenses won’t work with those cameras. You can still take pictures with the camera, but you will have to focus manually before pressing the shutter button. If autofocus is important to you, make sure you only buy a Nikon lens from the AF-S or AF-I series.

Smart shopping

While you can walk into a camera store, ask a few questions, and walk out with an expensive lens, doing a little research ahead of time can help prevent buyer’s remorse.

Read Reviews It’s always good to get a sense of how people who have bought a product feel about it. I go to a couple of Web sites for lens reviews. The first is PhotographyReview.com, which lists more than 900 lenses-200-plus of which have been rated by five or more people. Another good option is SLRgear.com, which reviews lenses for most of the major camera systems. You can also find commentary about lenses in the forums at Digital Photography Review. Finding the information can require some digging, but I’ve found the effort worth the time. DP Review started formally reviewing lenses earlier this year, but there are only a handful of reviews at this time.

Try Before You Buy I’ve found that the best way to determine if a lens will work for me is to rent it. Many camera stores that cater to the pro photographer will let you rent popular lenses for a weekend at a reasonable price.

If you can’t find a local store, go online. Rentglass.com rents lenses for Canon and Nikon DSLRs on a weekly basis. This is not only a great way to test a lens out, it also lets you take a fancy lens with you on vacation. While the rental rates aren’t inexpensive, they’re a bargain when you want to play with a $1,500 extreme-wide-angle lens that you could never justify buying. Make sure you opt for the insurance coverage, however, or check with your credit card company about damage claims: you don’t want to end up with a $1,500 paperweight.

Get a new view

In the end, choose the lens that best fits the type of shooting you want to do. But don’t be afraid to play around. You’ll find that adding a second (or third) lens-and using it regularly-will help you become a better photographer, just by changing your perspective as you look through the viewfinder.

[Rick LePage is the editor in chief of the “Photoshop Elements Techniques” newsletter. He also runs the photo-printer Web site Printerville.]

Subscribe to the Best of Macworld Newsletter

Comments