Buyer's Guide 2007: Lens Strategy
How to select the right mix of lenses for your photography
To get the most out of your D-SLR system, you'll want to choose a variety of lenses that offer the focal lengths, speed and features that match well with your favorite subjects. The key to selecting the right lenses is in understanding their capabilities and limitations and the types of photography and situations to which each is best suited.
First, we'll examine the basics of lens design and performance, then we'll explore the general categories of lenses that address particular photographic needs.
FOCAL LENGTH, PRIME AND ZOOM
The first and most obvious lens feature is focal length. This millimeter measurement ultimately represents the area of coverage and magnification that a lens provides. A short focal length (like 15mm) provides a wider angle of view without much magnification and a long focal length (like 200mm) provides much more telephoto enlarging power.
In the 35mm film format, wide-angle lenses are usually considered anything less than 40mm. At the opposite end of the spectrum are telephoto lenses. Again, in 35mm terms, these lenses have a focal length of 60mm or more. Lenses between 60mm and 100mm are often called short or medium telephoto lenses. Between the wide-angles and telephotos are "normal" lenses. With a range of 40mm to 60mm in 35mm film terms, these lenses are designed to approximate the view of the human eye. When any of these lenses has a fixed focal length, it's called a prime lens. In lieu of primes, some photographers opt for zooms-a single lens that offers a range of focal lengths in a single package.
Unlike 35mm cameras, digital cameras vary in sensor size, and this directly impacts the angle of view a particular focal length provides. D-SLRs that are referred to as "full-frame" have sensors that match the size of the 35mm frame. When you mount a 35mm lens to a D-SLR with a full-frame sensor, that lens behaves as described above.
However, most consumer-class D-SLRs have sensors that are smaller than a 35mm frame, and when paired with a 35mm lens, create a telephoto effect, usually around 1.5x magnification. That means that a 24mm lens will actually provide an angle of view equivalent to a 36mm lens. Keep this in mind when shopping for lenses if you don't have a full-frame camera. This fact can be a boon for telephoto work, but it also means you need an even wider lens to do wide-angle photography.