Do You Need a Telephoto Lens?
By Ron Spomer
The image of the consummate wildlife photographer is a guy or gal with a big camera hanging from one shoulder and a honking huge telephoto lens mounted to a huge tripod with a rather puny looking (by comparison) camera stuck to it.
Big lenses are a big deal.
But do you need one for your nature photography?
If you’re hoping to capture full-frame to nearly full-frame images of wild creatures, a telephoto lens will increase your success dramatically. Magnification is the reason. Like a binocular or telescope, a telephoto lens enlarges the view. But instead of rating lenses by magnification power, such as 8X or 10X, photographers measure by focal length in millimeters – literally the distance from the front lens element (objective lens) to the rear focus plane. We can convert those millimeters into more familiar X powers by doubling the first number and designating it as the magnifying power. This means a 400mm telephoto lens magnifies its view by 8X. A 500mm lens is like a 10X binocular (without the binocular view, of course. A photo lens is a monocular.) And a 600mm would equate to a 12X, etc.
What size do you need? Depends on what you’re shooting. For really big, really accommodating animals in controlled settings like parks and zoos a 300mm tele can be sufficient. In the wild or when photographing birds and small mammals you might find 800mm a bit short. And quite heavy.
Yes, logistics do become an issue. Bulk and weight are obvious challenges. Canon’s superb 400mm f/2.8L IS USM lens weighs nearly 12 pounds. The 800mm f/5.6 is “just” 10 pounds, but it’s 18 inches long. How far do you want to carry something like that?
When you’re contemplating size and weight, think long and hard about the diameter of the objective lens, too. Lenses are rated by maximum f-stop, i.e. f/2.8 or f/4 or f/8. This is the aperture, or hole in the lens through which light passes. It’s diameter is controlled via a diaphragm plate, a series of metal blades within the lens that open and close as you change the lens’ f-stops. The lower the number, the bigger the hole and the brighter the image. F/2.8 = big hole. F/16 = little hole.