Digital lenses are without doubt one of the most important weapons in a photographer's arsenal. They are also one of the most variable, coming in every conceivable weight, size and focal length, from the widest 10mm fish-eye to the longest 800mm telephoto lens. Whether your passion is to isolate fine architectural detail, or you are a landscape photographer looking to capture dramatic sunsets, there are many options for lenses, but they fall into four main categories.
Standard
Standard lenses for full-frame digital SLR cameras fall between 40mm and 55mm, 50mm being the accepted norm. Standard lenses are closest to the normal field-of-view of the human eye, offering undistorted perspective. They are often used for portrait photography. Many digital SLRs need a shorter focal length than a 35mm camera or full-frame digital camera, due to their smaller APS-sized sensor, and these cameras will need a 35mm lens to get the same field-of-view as a 50mm lens on a full-frame.
Wide-angle
Wide-angle lenses are well suited to landscape and reportage photography, with their wider angle-of-view and shorter focal lengths than standard lenses. The need for shorter focal lengths to compensate for the APS sensor on many digital SLRs has led to an influx of new models. A typical digital wide-angle model might be 17-35mm, giving an equivalent field-of-view to 25-52mm on a full-frame SLR.
Macro
If you've ever looked at a full-frame picture of a small subject such as an insect or petals and wondered how it was achieved, the answer is by using a macro lens. Macro lenses focus from as close as 2 inches and allow for a 1:1 life size reproduction. These lenses are specifically designed for close-up photography and are usually available in focal lengths from 50mm to 180mm.
Telephoto
Any digital camera lenses with a focal length above 50mm is designated as telephoto. Portrait photography is ideally suited to short telephoto lenses (70mm to 120mm) and longer focal lengths (135mm to 300mm and beyond) are excellent for wildlife and sports photography. On most digital SLRs, with smaller APS-sized sensors, the magnification of a lens is increased by approximately 1.5 times, making a 200mm digital lens equivalent to 300mm on a full-frame camera
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