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The Tele Extender – a lightweight telephoto
The above advantage is quite important,
because there is a loss of lens speed with any extender. A 2x extender
will double the focal length of a prime lens, but it will also steal two
f-stops. A 135mm telephoto lens, for example, can become equivalents of
270mm with a 2x extender in place. If the lighting conditions call for
f/8 with a prime lens alone, they will now require two additional f-stop
(f/4) with the accessory. However, if the maximum aperture of your 135mm
lens is only f/4 and you have to step down to get a sharper image, it
means only a slower shutter speed will produce the correct exposure.
With 27mm of magnification that could mean un-sharp picture just from
camera movement. Therefore, it is easy to see why being able to use tele
extender wide open is so convenient. Because the speed loss accompanying
tele extender use, some manufacturers provide 1.5x extenders. They don’t
magnify as much, but they don’t require as much exposure increase
either.
Extender can be used in combination of
further augment lens power, but the practice is not advisable. Using two
extenders at the same time will only add to any sharpness problems, and
exposures loss can be extreme. A firm tripod and a slow shutter speed
may be the only answer in such a situation. A through the lens automatic
exposure camera will do all the exposure calculations for you, but if
you are using a manual camera, some on the spot math will be needed.
Tele extenders are available in manual
versions, but the trend is to automatic functioning so that none of the
auto features of the prime lens are lost. Some manual units allow
removal of glass elements so that the barrel can serve as an ordinary
extension tube.
While tele extenders cost lens speed and
occasionally some sharpness, they do provide real advantages. They are
compact and lightweight compared with prime lenses of the size they
replace, and they are certainly less expensive. The size/weight
advantage is especially important to a traveler attempting to get the
most versatility from the least amount of equipment. With 50mm and 200mm
prime lenses plus a 2x extender, two extra focal lengths (100mm and
400mm) can be had for no more cost or weight than that of the extender
alone. Although a prime telephotos lens is usually more desirable than a
lens/extender combination, there are times when a tele extender can make
your photographic work much easier. _________________________________________________________________________
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Short Telephotos Lens
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