Now that you've invested in a DSLR camera, what lens should you buy? First, you need to understand focal length, the most important lens specification.
What is focal length and why do I need to know about it?
Focal length defines the distance from the first glass element of a lens to the point of focus. The distance is typically measured in millimeters (mm). Generally, the greater the mm rating on a lens, the more magnification the lens provides. Focal length determines how much you can fit into a photo. Wide-angle lenses fit more into your photo and work nicely for indoor pictures as well as landscapes. Telephoto lenses allow you to enlarge a subject when you cannot get physically close. These are ideal for wildlife photos.
Now let's check out the different types of lenses and how different features affect the types of photos you take.
Types of Lenses
Fixed Focal Length (includes fixed or prime lenses and normal lenses) Non-zoom lenses have only one focal length and are known as fixed or "prime" lenses. Fixed lenses generally offer good image quality, higher light sensitivity, and are smaller and lighter. Fixed lenses are ideal for portrait photography when you are taking a lot of pictures at the same focal length.
Short-Range Zoom(includes zoom or compact zoom lenses) A short-range zoom lens is a standard, all-purpose lens, typically around 18–55mm (3x optical zoom equivalent). It lets you vary the focal length somewhat with a shorter range for zooming in and out. These are ideal for everyday photography, but do not allow for distant zoom capabilities. Some compact zoom lenses feature image stabilization to compensate for camera shake, and provide incredibly crisp, clear images.
Long-Range Zoom (includes telephoto and zoom lenses) A zoom lens allows you to vary the focal length and makes the lens more versatile, dramatically expanding your shooting options. When you zoom in, the focal length increases; as you zoom out, it decreases. Generally 70–200mm or higher (up to 600mm), long-range zooms are great for dramatic shots of distant objects. They allow you to get close to your subject from a distance. Specific long-range zooms or telephoto lenses have a focal length higher than 70mm. However, the longer the focal length, the more likely it is to produce blurry photos, especially when there isn't enough light. Many models are now being manufactured with image stabilization to correct this.
A wide-angle lens refers to a lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane. This type of lens allows more of the scene to be included in the photograph, which is useful in architectural, interior and landscape photography where the photographer may not be able to move farther from the scene to photograph it.
Image Stabilization Many lenses now come with built-in optical image stabilization (sometimes referred to as vibration reduction), that moves the lens elements in an attempt to counteract any sensed motion of the camera. This results in fewer blurred photos and is especially useful when you are zooming in low light or shooting with slower shutter speeds.
Fisheye Fisheye lenses offer a full 180-degree viewing angle, but the image is distorted so the center looks like it's closer to you and the edges look like they're receding. It's a fun, distinctive effect, useful when trying to capture a wide, nearby scene. However, a fisheye lens will probably not become your standard-use lens.
f/2.8 or Wider Aperture Aperture is the opening in your camera lens that determines the amount of light that passes through to the sensor. By using a lens with an f/2.8 or wider aperture, you can fade the background and focus on your subject in the foreground. You'll get a much more dramatic shot as your subject will "pop" from the photo. The result is a more desirable image with less "depth of field," or a more diffused background.