BetterPhoto Q&A
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Telephoto & Zoom Lenses

What is each best used for?

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December 30, 2000

I presume you are asking these questions as you are building, or about to build an SLR system allowing interchangeable lenses.

=== Telephoto ===

A "telephoto" is any lens with a longer focal length than a "standard" lens. A "standard" lens is one that approximates the perspective of the unaided human eye and the "rule of thumb" for this is a focal length equal to the diagonal of the film frame. For small format 35mm this works out to about a 43mm focal length. The "standard" focal length in 35mm format is 50mm, a bit longer, but is a vestige of the Leica "A" which was the first successfully marketed 35mm camera. Any 35mm format lens between 40mm and 55mm is considered a standard.

Technically, the telephoto lens is a design category for longer focal length lenses, which are physically shorter than the focal length. The entire class of lenses with focal lengths longer than a "standard" is more accurately called a "long" lens. This is an older term not used much any more and "telephoto" is applied to nearly everything longer than a standard one. Lenses shorter than a standard are called "short" or "wide-angle" lenses.

A telephoto lens will make objects look closer, especially more distant ones compared to closer ones, and can make objects of different distances in an image appear closer together. This "flattens" the depth in an image.

I have uploaded two images made from nearly the same location using two different telephoto lenses. The first was made with a 200mm and the second with a 135mm. Note how the distant bluffs look much larger and closer in the first than in the second. Now look at the fence posts which are the same ones, and were kept about the same size by moving the camera position. The bluffs are still larger than how the unaided human eye would perceive them. In the case of the first, the 200mm was used to make the bluffs taller than the tractor to create a complete backdrop for it. In the second, the 135mm was used to make the tractor in the distant field appear just large enough without compromising a sense of expansiveness. This is called "image management." The camera position was moved by about 20 feet or so to keep the fence posts the same size while keeping the tree branches along the image top. (This is "framing," a composition technique.)

=== Zoom ===

Used alone, "standard," "long," "telephoto," "short," and "wide-angle" imply a "prime" lens which is one that has a single focal length. A "zoom" lens can vary the focal length continuously over a range. This range can cover short, standard and long focal lengths (35-105mm), or just short ones (24-48mm), or just long ones (75-150mm).

The question often follows that with availability of zoom lenses, why would one want primes? The answer is a zoom is *always* a compromise. The design of a prime can be optimized for a single focal length in speed, resolution, contrast, flare, control, aberration corrections, and "bokeh." While some zoom lenses are very, very good, there will be compromise(s) in their designs. This is done to allow reasonable performance across the entire focal length range. Almost always the first compromise is lens speed. Beyond that, one usually finds some pincushion or barrel distortion (a form of aberration). Some contrast is lost and flare control is difficult; a zoom has many more glass elements than a prime. Zoom designs have gotten better than they were 25-30 years ago.

In spite of the compromises, a zoom can be very useful for a number of situations, especially those that demand traveling very light or do not allow interchanging lenses easily. However, a zoom should not be a replacement for good image management and composition. The two images uploaded give an example of this; the camera position was moved for composition reasons in addition to changing focal lengths. Because of the design compromises, a zoom does not replace good prime lenses; it supplements them. A zoom, such as a 35-105mm, is often bought as a "first" lens in a 35mm SLR system, particularly to keep the initial cost down. For the serious and professional photographer, the eventual goal should be good primes. The first prime should be a 50mm standard lens (for 35mm format).

-- John

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December 30, 2000

To be specific, I have a Nikon N80 and that I am just beginning to grow into and am looking for the best lens to add to this. I am heading off on a safari in a few months and want a lens that would be best suited for these types of photo opps.

Could you name a specific lens?

Thanks for letting me pick your brain!

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January 05, 2001

Jim

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January 22, 2001

	Awaiting its Farmer as the New Day Begins Done using a 200mm telephoto. Note size of fence posts in foreground and height of bluffs in background. John A. Lind
	Working the Fields Done about an hour later with a 135mm telephoto. Note the fence posts are the same size, but distant bluffs look smaller. This is the image management and perspective control I was talking about. John A. Lind

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January 24, 2001