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Lens selection


A fish-eye lens has an angle of view greater than 180 degrees.
A fish-eye lens has an angle of view greater than 180 degrees.

There are several types of lenses available for cameras that offer lens interchangeability. The main differentiation is in focal length, however other characteristics provide lenses with the ability to perform specialized functions that could not otherwise be achieved.

PRIME and ZOOM LENSES

You may hear the term "prime lens," and wonder what it means. A prime lens has a fixed focal length (FFL), as opposed to a zoom lens, which has a variable focal length (VFL). An example of a prime lens would be a 105 mm lens. An example of a zoom lens would be a 28 mm to 70 mm lens. Prime lenses generally have better optical quality than a zoom lens, and usually have a wider maximum aperture.

THE NORMAL LENS

This is the type of lens that was, until recently, typically supplied with a new camera. It is a fixed focal-length (non-zoom) lens that is called “normal” because the scene we see through it is more or less the same scene when viewed by the naked eye.

Many digital and traditional film cameras today come equipped with a zoom lens rather than a normal lens. The focal settings for the zoom lens usually include one that is the range of a normal lens. For example, a normal lens for a 35 mm camera is about 50 mm, and many zoom-equipped cameras have lenses that cover a range from, say, 28 mm to 70 mm.

The normal lens, however, generally has capabilities beyond those of the average zoom lens, and there are advantages in owning one. It is usually a fast lens, meaning that its maximum aperture is very wide, often in the range of ƒ/1.2, ƒ/1.4 and ƒ/1.8, permitting you to take pictures in low light with faster shutter speeds. It is also typically a sharp lens that is bright and easily-focused, with distortion-free images that have excellent resolution and color rendition. Many are autofocus, and some step down to apertures as low as ƒ/22 for extended depth of field. Some also have macro capability, making them dual purpose.

The normal lens is a good general purpose lens, useful in everyday situations, including candid photography, landscapes and low-light work.


THE WIDE-ANGLE LENS

The terms “wide-angle” and “telephoto” are based on the different angles of view they provide when compared with a normal lens. A wide-angle lens captures a wider angle of view than a normal lens does. There is no single wide-angle lens, but rather a variety of lenses that give wider and wider angles of view, some of which are classified as super or ultra wide-angle lenses, and the widest of all - fish-eye lenses.

Lenses considered to be wide-angle include the 35 mm, 28 mm and 24 mm varieties, with the 28 mm being the “standard” wide-angle lens. Super wide angle lenses then take over, and run from 20 mm to about 13 mm.

Wide-angle lenses provide large depth of field, making it simple to have foreground and background in focus. Because they take in such wide areas (angles of view), they are excellent for working in tight spaces, such as building interiors, or close-up group pictures. Most wide angles tend to show distortion, just like when you look into a curved mirror, particularly when a subject is photographed close-up. They are extremely handy when you don’t have time to focus accurately or compose properly, because they take in the whole scene and most of it will be in focus. No photojournalist would be without one. They are also ideal for landscapes, taking in large areas of ground and sky, and travel photography, but are impractical in photographing close-up portraits or small subjects up close since they throw perspective off.

A fast, sharp 24 mm is a great wide-angle lens for general applications.
A fast, sharp 24 mm is a great wide-angle lens for general applications.

Some fish-eye lenses produce a circular image.
Some fish-eye lenses produce a circular image.

THE FISH-EYE LENS

The fish-eye is a super, ultra, really-wide-angle lens, providing a angle of view of 180 degrees and more - so wide that the photographer’s feet or tripod legs can appear in an image taken horizontally. This lens is not corrected for linear distortion, which means that straight lines, especially at the edges of the viewframe, will be curved beyond the point of exaggeration. Some fisheye lenses produce a circular image, as shown on the left.


This is an extreme lens, and is used to make images not meant to have normal perspective. Depth of field is phenomenal. This lens is for the inventive, selective photographer, since every image it takes will look unusual and too many of them will cause the viewer to begin yawning. It is great for capturing overall crowd scenes, such as at a football stadium, and pictures where other focal length lenses can’t get the total view and the special effects look of a fisheye.

A 17 mm lens is a super wide-angle lens, ideal for landscapes and for shooting in a confined space.
A 17 mm lens is a super wide-angle lens, ideal for landscapes and for shooting in a confined space.

A super-telephoto lens can bring in far-away objects barely discernible to the human eye.
A super-telephoto lens can bring in far-away objects barely discernible to the human eye.

THE TELEPHOTO LENS

Telephoto lenses give a narrower view than the normal lens. Their focal lengths are long and their angles of view are narrow.

They come in different focal lengths, with the longest (and most costly) ones approaching the ability of telescopes to magnify images. Image magnification is not the sole purpose of telephoto lenses. Their inherent shallow depth of field makes them useful in eliminating unwanted foreground and background objects by simply throwing them out of focus. Also, their foreshortening characteristic can make portraits look much more pleasant and natural, and can visually compress distant objects so they don’t look so far away. The setting sun, for instance, can seem so much larger and closer when photographed through a telephoto lens.

Image magnification, however, is an important characteristic of very long telephoto lenses. Have you ever wondered how a sports photographer can capture an image of a high jumper or pass receiver that looks as though he or she was ten feet in front of the athlete? The magnifying ability of super telephoto lenses makes such images possible. The photographer may have been fifty yards away, but the close-up image was made possible thanks to a high-powered telephoto lens.


Telephoto lenses require accurate focusing since they have inherent shallow depth of field. Because their angle of view is so narrow and their weight can be considerable, a tripod is recommended to ensure continuous, accurate subject placement. Their longer focal lengths also make hand-holding the camera less of an option since shutter speeds must be fast to avoid blur from either camera or subject movement. If you use a long focal length telephoto lens, you should also use a sturdy tripod to ensure sharp pictures.

MODERATE TELEPHOTO LENSES

Moderate-length telephoto lenses (85 mm to 130 mm lenses for 35 mm cameras) can be hand-held when shutter speeds are fast enough, and are ideal for portrait work, especially headshots and head and shoulder pictures. In fact, the 105 mm is considered to be the classic portrait lens.

Even a 200 mm lens can be easily hand-held when shutter speeds exceed 1/200 second. (See Slow shutter hand holding for information on using your camera without a tripod.)

These lenses are also great for bringing landscape and cityscape details closer, and for shooting scenes from a crowd - including parades, stage shows and even your children’s Christmas pageant - when you are unable to get physically closer.

MEDIUM TELEPHOTO LENSES

135 mm to 300 mm lenses for 35 mm cameras are considered to be medium telephoto lenses, distinguishing them from moderate and super-telephoto lenses. They are right in the middle.

A fast 135 mm lens is a practical lens for candid wedding photography and for action shots when the subject is neither close nor distant, since it’s not too heavy, can easily be hand held and is great for singling out your subject. It’s a good lens for portraits, too.

The 180 mm to 200 mm lens is ideal for sports when the action is taking place just in front of you. If you are way off in the bleachers, you’ll need a more-powerful lens. Lenses in this range are also good lenses for news photography. The speed of the lens is critical at this focal length. A slow 180 mm lens will find little use, whereas a fast 200 mm lens may be your most-used candid lens since it brings the action close while allowing you to use fast shutter speeds to capture it.

A 300 mm lens does everything a 200 mm lens will do, except it brings subjects even closer. The problem with lenses in this size is that the best ones - those that are fastest - are quite expensive. We question the merits of buying a 300 mm lens for action photography when its maximum aperture is ƒ/5.6 or even ƒ/4, because the shutter speeds required are often so slow that you sometimes can’t capture fast-moving images without subject blur, even when using fast film. But, a 300 mm lens that has a very wide ƒ/2.8 maximum aperture is quite costly. Of course, if you don’t need fast shutter speeds when you use your 300 mm lens, then it needn’t be a fast lens, but the use of a tripod is essential.

SUPER-TELEPHOTO LENSES

Powerful telephoto lenses from 400 mm to 800 mm and up are expensive, even for the slower varieties, but they deliver the ultimate in telephoto photography. Deep pockets are needed for all the lenses in this range, especially the fastest versions, since a single lens can cost more than the average consumer may spend on photography in a lifetime.

A high-quality 400 mm ƒ/2.8 lens is the dream lens of many a sports and wildlife photographer, something they may save for years to purchase. A 600 mm ƒ/4 lens is even more exotic, but the 16-times magnification of an 800 mm ƒ/5.6 lens can even be used for astrophotography with sharp, colorful results.

Professional photographers are the primary users of such fabulous lenses. Many of the images we see in newspapers, and sports and action magazines are taken with these lenses.

MACRO LENSES

A macro lens may have a focal length of, say, 60 mm or 105 mm, but is differentiated from other lenses in these focal lengths by its ability to extend out a longer distance to permit focusing only a few inches from the subject. A 55 mm or 60 mm macro lens is a normal lens and a 200 mm macro lens is a telephoto lens, but their ability to focus extremely closely allows macro lenses to capture images of tiny objects in frame-filling, larger-than-life sizes.

Dedicated macro lenses are generally expensive, but they avoid such problems as color fringing and optical distortion. They usually have quite small minimum apertures in order to maximize the depth of field. The closer your lens is to a subject, the less depth of field you will have at any given aperture. When you are extremely close, depth of field may be a fraction of an inch. You need to set small apertures, like ƒ/16, to ensure your subject will be acceptably sharp.

ZOOM LENS

A zoom lens allows you to change focal lengths without changing lenses. It has variable focal lengths, enabling it to be used as a wide-angle lens for one exposure, then as a normal or telephoto lens for another, depending on its range of focal lengths. Some zooms cover a range of mainly telephoto settings, from 70 mm to 300 mm, for example, or 80 mm to 200 mm, whereas others provide a selection of wide-angle focal lengths, such as 17 to 35 mm. Popular, all-around-use zooms range from moderate wide-angle to moderate telephoto.

A zoom’s range is generally indicated by its widest and narrowest focal lengths, for example 70-300 for a lens that zooms from 70 mm to 300 mm. There is often an arrow between the numbers to indicate that it is a zoom.

Zoom lenses provide the photographer with flexibility in framing images while remaining in one camera position. With a 70-300 zoom, for instance, you can take a three-quarter-length shot of someone at the 70 mm setting, a head and shoulders portrait at 105 mm, and shoot a distant wild animal at 300 mm.

The main disadvantages to zoom lenses are that they are often heavy and slow. Many have maximum apertures no faster than ƒ/4 or ƒ/3.5 at their widest focal length. High-quality, faster zoom lenses can be prohibitively expensive, if available at all for your camera model. A good quality zoom lens is of particular use in aerial photography and for speed and versatility when photographing weddings.

Further information...

Using 35mm SLR lenses on dSLR camera bodies
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