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Telephoto Lenses
By definition, a telephoto
lens is one whose focal length is greater than that of a normal lens.
The longer the focal length of the lens, the greater the degree of magnification.
In fact, the magnification is mathematically related to focal length.
For example, a 100mm lens produces an image exactly twice that of a normal
lens. A 400mm lens gives you an image size eight times your normal lens.
As the lens lengthens, some interesting things happen. The len's angle
of view becomes narrower and depth-of-field becomes shallower. A narrow
angle of view enables you to isolate a detail in a distant building or
eliminate a cluttered foreground. A shallow depth-of-field is great for
blurring distracting backgrounds so that attention is directed towards
your subject such as an outdoor portrait.
By far, the most useful telephoto lenses are those with medium focal lengths...between
85mm and 200mm. Because they minimize facial distortion and allow a comfortable
distance between photographer and subject, medium telephotos are ideally
suited for portraits. In addition, they are perfect for many other situations
in which you have to keep a moderate distance from your subject such as
candid street shots or animals at the zoo.
Telephotos lenses of 300mm or longer are usually for specialized demands
and would be too powerful for ordinary usage. However, if you have a keen
interest in wildlife photography or prefer huge suns in your sunset shots,
then these and longer lenses may be for you. For the occasional "long
reach", a tele-extender combined with your telephoto will work just fine.
Remember, because the magnification of telephoto lenses accentuates the
effect of camera movement, faster shutter speeds are required. To obtain
a sharp picture, the rule of thumb is to use a shutter speed closest to
the focal length of the lens. For a 135mm lens, handhold at no slower
than 1/125 second. With a 200mm lens, you should be at 1/250 second. If
slower shutter speeds are needed because of low light or small aperture
requirements, better get out your tripod.
So "reach out" to new and exciting photographic horizons...with telephoto
lenses!
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