Tuesday, April 21, 2009
The Poor Man’s Super-Telephoto
Using a tele-extender can give your long lenses even more punch for wildlife and landscape photos
Also known as tele-extenders, teleconverters are available from the major lens manufacturers for their long lenses, and offer three major benefits.
First, as just cited, they’re an economical way to get superlong focal lengths. And they’re not just for the budget-challenged. Pros use them, too—a 1.4x converter turns that monster 600mm into an 840mm; a 2x converter, into a 1200mm.
The second benefit of the teleconverter is that it doesn’t change the lens’ minimum focusing distance. Add a 2x converter to a 300mm lens that focuses down to five feet, and you have a 600mm lens that focuses down to five feet. (For comparison, my camera manufacturer’s 600mm super-telephoto won’t focus closer than 18 feet unless you attach it to an extension tube; but then it won’t focus out to infinity.)
Of course, teleconverters do have some drawbacks, the biggest being that they reduce the amount of light transmitted to the film or image sensor—by 1 stop for a 1.4x converter, 1.5 stops for a 1.7x converter, and 2 stops for a 2x. Add a 1.4x converter to a 300mm ƒ/4 lens, and it becomes a 420mm ƒ/5.6. Add a 2x converter to the 300mm ƒ/4, and it becomes a 600mm ƒ/8. TTL metering automatically compensates for the light loss, but the necessarily slower shutter speed reduces action-stopping power.
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