Arguably the most important weapon in a photographers' arsenal, lenses are also one of the most variable. From the widest 10mm fish-eye to the longest 800mm telephoto, optics are available in every conceivable size, weight and focal length. Due to the smaller sensors used in many of today's digital SLRs, however, focal lengths vary depending on the model in question.
But whether you're a landscaper looking to capture dramatic sunsets or an architectural fanatic looking to isolate fine details, there's a multitude of options that fall into four categories. Here's the low-down.
On full-frame digital SLRs standard lenses fall between 40mm and 55mm, though 50mm is the accepted norm. You'll need a 35mm lens to get the same field-of-view on digital SLRs with the smaller APS-sized sensor. Closest to the field-of-view of the human eye, standard lenses offer an undistorted perspective and are often used for flattering portraits. Just for the record, the true field-of-view of the human eye is 43mm!
With shorter focal lengths and wider angles-of-view than standard lenses, wide-angle lenses are employed by landscape and reportage specialists. Remember you'll need a shorter focal length on many digital SLRs than a 35mm or full-frame digital model. This need for shorter focal lengths on many digital SLRs has produced a raft of new models. A 17-35mm model, such as the one shown below, gives a field-of-view equivalent to 25-52mm on a full-frame SLR.
If you've ever wondered how photographers fill the frame with small subjects such as petals and insects, the answer is the humble macro lens. Allowing for 1:1 (life-size) reproduction and focusing from as close as 2in, true macro lenses are specifically constructed for close-up photography. They are commonly available in focal lengths between 50mm and 180mm.
Any lens that weighs in with a focal length above 50mm is said to be a telephoto lens. Short telephotos (between 70mm and 120mm) are ideal for portraiture, while longer focal lengths (between 135mm and 300mm and above) are perfect for sports and wildlife. Remember, the magnification of a lens on most digital SLRs is increased by around 1.5x, so a 200mm lens is equivalent to a 300mm on a full-frame camera.
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