Photography
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?
Probably.
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.
Put another way, an f/2.8 lens will let you shoot at a faster shutter speed – say 1/1000th of a second. Under the same lighting conditions an f/4 lens would reduce that to 1/500th and an f/5.6 would drop it to 1/250th. You don’t even want to know what an f/22 would do. Well, maybe you do. F/22 would dim the lights so far that you’d need to keep your shutter open for 1/15th second, during which time you’re going to shake and your subject is probably going to move, yielding a classic “what’s that?” out of focus image. Under the low lighting often found outdoors when game is afoot, a larger maximum lens aperture could save the day. You might get a sharp image of a walking whitetail with an f/2.8 lens while an f/5.6 might demand a shutter speed so slow that the animal would be blurred.
But there is a compromise. You can increase the ISO on your camera. This essentially increases the camera’s ability to absorb light quickly. The higher the ISO number, the faster it sucks up the light, so the shorter your shutter speed needs to be. The downside is that faster ISO speeds increase “noise” (known as “grain” in the bad old days of film.) Fortunately, the latest digital cameras control noise quite well, so you can push ISO to 1,000 and even 2,000 and still get good results. This suggests you can “get by” with smaller diameter, smaller maximum aperture lenses. Whereas an f/2.8 was essential for low-light, telephoto work 10 years ago when high-quality film ISO speeds hovered around 100, an f/5.6 might suffice today.
Of course, you can always shoot exclusively atop a tripod using long shutter speeds. A rock will look just as sharp on an 8-second exposure as a 1/800th exposure as long as the camera does not move. But wildlife has a habit of moving faster and more often than rocks.
Another feature of a wide aperture like f/4 or f/2.8 in a telephoto lens is pleasantly blurred backgrounds. Because depth-of-focus decreases as lens length increases, the images created via long telephotos stand in sharp focus against soft, out-of-focus backgrounds and foregrounds. Additionally, angle of view is minimized, further eliminating distracting elements around the subject. This is the classic, tell-tale look of a powerful telephoto image – sharp subject isolated against a wash of color. Looks great with flowers, birds, and pretty girls as well as wildlife.
If all this seems like too much information to absorb all at once, here’s a simple answer to the telephoto question: if you want to photograph wildlife, get at least a 300mm lens and preferably a 400mm or 500mm with at least an f/5.6 maximum aperture. Anything more powerful than that becomes difficult to handle for a lot of reasons.
In our next installment we’ll discuss an inexpensive option for increasing the telephoto effect with minimal added weight.