Telephoto Lens

Photography Resources

A photographic lens system specially designed to give a large image of a distant object in a camera of relatively short focal length. A telephoto lens generally consists of a positive lens system and a negative lens system, separated by a considerable distance. In these lenses the optical center lies outside of its physical construction, such that the entire lens assembly is between the optical center and the focal plane. A regular lens of a focal length that is longer than what is considered a normal lens is not necessarily a telephoto lens. A telephoto lens has to incorporate a special lens group known as a telephoto group (see below); nevertheless, non-telephoto lenses of long focal length are often informally referred to as telephoto lenses. The angle of view created by a telephoto lens is the same as that created by an ordinary lens of the same specified focal length. A telephoto lens can be either a prime lens or a zoom lens and work with single lens reflex film cameras as well as digital SLR cameras

Example of a 500 mm lens that is not a telephoto lens.

Sigma 50-500 mm 10x HSM zoom lens. Think of it as a 500 mm telephoto lens with a reverse zoom that works with digital cameras

Telephoto lens defined

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

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

Image magnification, is the most important characteristic of very long telephoto lenses. A sports photographer can capture an image of a high jumper or pass receiver that looks as though he or she was just a few feet in front of the athlete. The magnifying ability of super telephoto lenses allows such images to be possible. The photographer may have been seventy yards away, but the close-up image was made possible because of a powerful telephoto lens.

Telephoto lenses require precise focusing as they have an inherent shallow depth of field. As their angle of view is so narrow and the lens can be quite heavy, 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 camera blur or subject movement. When using a long focal length telephoto lens, it is imperative to use a quality tripod to ensure sharp pictures.

Moderate Telephoto Lenses

Moderate-length telephoto lenses (85 mm to 130 mm lenses for 35 mm cameras) (55 mm to 85 mm for APS-C cropped sensor cameras) can be hand-held when shutter speeds are fast enough, and are ideal for portrait photography, 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 Shutter speed for information on using your camera without a tripod.)

When you are unable to get physically closer, these lenses are also great for bringing landscape details closer, and for shooting crowd scenes, including parades, stage shows and even your children’s school events.

Medium Telephoto Lenses

135 mm to 300 mm lenses for 35 mm cameras (90 mm to 200 mm for APS-C cropped sensor cameras) are considered to be medium telephoto lenses, setting them apart from moderate and super telephoto lenses.

A fast 135 mm lens (90 mm for a cropped sensor camera) 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 is also a good portrait lens.

The 180 mm to 200 mm lens is an ideal sports range when the action is taking place just in front of you. If you are far off up in the bleachers, you’ll need a more-powerful lens. Lenses in this range are also good lenses for photojournalism. The speed of the lens is critical at this focal length. A slow 180 mm lens will have little use, and a fast f/2.8 200 mm lens will most likely be your most-used candid lens since it allows you to use fast shutter speeds to bring the action close and 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 fastest ones are seriously expensive. I question any merits of buying a 300 mm lens maximum aperture is ƒ/5.6 or even ƒ/4 for action photography, because the shutter speeds required are often so slow that many times you will not be able to capture fast-moving images without subject blur, even when using fast film or a high ISO setting. But, a 300 mm lens that has a fast 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 still essential.

Super Telephoto Lenses

Powerful telephoto lenses from 400 mm to 800 mm and up are expensive, even for the slowest versions, but they deliver the ultimate telephoto photography. Deep pockets are needed for all the lenses in this range, especially the faster versions, since a single lens can cost upwards of $9,000 which is more than an average consumer may spend on photography in their lifetime.

A high-quality 400 mm ƒ/2.8 lens is the dream lens of many sports and wildlife photographers, 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 exotic lenses. Many of the images that we see in newspapers, and sports magazines are shot with these lenses.

Construction

If a camera lens were to be constructed from a single lens of 200 mm focal length, then when the lens is focused on an object at infinity, the lens will be 200 mm away from the focal plane where the film or sensor is. The center of the lens is referred to as the optical center of the lens. Even constructing the lens out of several elements to minimize aberrations, will still have the optical center within the construction.

As the focal length of such lenses increases, the physical length of lens becomes inconveniently long. But such lenses are not telephoto lenses, no matter how extreme the focal length. They are simply known as long focal length lenses. A telephoto lens works by having the outermost (i.e. light gathering) element of a much shorter focal length that the equivalent long-focus lens and then incorporating a second set of elements close to the film or sensor plane that extend the cone of light so that it appears to have come from a lens of much greater focal length.

The diagram to the right shows the basic construction of a telephoto lens. It consists of front lens elements that, as a group, have a positive focus. The focal length of this group is shorter than the effective focal length of the lens. The converging rays from this group are intercepted by the rear lens group, sometimes called the "telephoto group," which has a negative focus. The simplest telephoto designs could consist of one element in each group, but in practice, more than one element is used in each group to correct for various aberrations. The combination of these two groups produces a lens assembly that is physically shorter than a long focus lens producing the same image size.

This same property is achieved with mirrors combined with lenses in catadioptric designs. The mirrors in such designs fold the light path and the curved secondary extends the light cone, making the lens much shorter than the focal length even given the folded design. However, lenses incorporating mirrors are not necessarily of telephoto design.

Compare with the opposite effect used in retrofocus lenses, sometimes described as inverted telephotos, which have greater clearance from the rear element to the film plane than their focal length would permit with a conventional wide-angle lens optical design. Zoom lenses that are telephotos at one extreme of the zoom range and retrofocus at the other are now common.

The heaviest telephoto lens was made by Carl Zeiss and has a focal length of 1700 mm with a maximum aperture of f/4, implying a 425 mm (16.7 inch) entrance pupil. It is designed for use with a medium format Hasselblad 203 FE camera and weighs 256 kg (564 lb).

Effects

Telephoto and other long-focal-length lenses are best known for making distant objects appear magnified. This effect is similar to moving closer to the object, but is not the same, since perspective is a function solely of viewing location. Two images taken from the same location, one with a wide angle lens and the other with a telephoto lens, will show identical perspective, in that near and far objects appear the same relative size to each other. Comparing magnification by using a long lens to magnification by moving closer, however, the telephoto shot appears to compress the distance between objects due to the perspective from the more distant location. Long lenses As a result give a photographer an alternative to the type of perspective distortion exhibited by shorter focal length lenses where (when the photographer stands closer to the given subject) different portions of a subject in a photograph can appear out of proportion to each other.

Long lenses also make it easier to blur the background more, even when the depth of field is the same; photographers will sometimes use this effect to defocus the background in an image to "separate" it from the subject.

If you are serious about landscapes, architecture photography, long telephoto shots or low light and night photography, a quality tripod and an even better tripod head may represent your best digital camera accessory. The importance of a good tripod can not be underestimated when you demand the ultimate image quality.

Still photography

Effect of different focal lengths on photographs taken from the same place: 28 mm 50 mm 70 mm 210 mm The above photos were taken using a 35 mm camera, using lenses of the given focal lengths.

Constant object size

The photographer often moves to keep the same image size on the film for a particular object. Observe in the comparison images below that although the foreground object remains the same size, the background changes size; As a result, perspective is dependent on the distance between the photographer and the subject. The longer focus lenses compress the perception of depth, and the shorter focus exaggerate it. This effect is also used for dolly zooms. The perspective of the so-called normal lens, 50mm focal length for 35 mm film format, is conventionally regarded as a "correct" perspective, though a longer lens is usually preferred for a more pleasing perspective for portraits. 28 mm 50 mm 135 mm

Teleconverter

A teleconverter is a secondary lens which is mounted between the camera and a photographic lens. Its job is to enlarge the central part of an image obtained by the objective lens.

History

The concept of the telephoto lens, in reflecting form, was first described by Johannes Kepler in his Dioptrice of 1611, and re-invented by Peter Barlow in 1834

Histories of photography usually credit Thomas Rudolphus Dallmeyer with the invention of the photographic telephoto lens in 1891, though it was independently invented by others about the same time; some credit his father John Henry Dallmeyer in 1860.

On the other side of the world, in New Zealand, Alexander McKay was taking photographs of exceptional quality using home-made telephoto lenses, (ground from the bottoms of whisky bottles), probably as early as 1883 or 1884. Some of his photographs are preserved in the holdings of the Turnbull Library in Wellington, and two of these can be unequivocally dated as having been taken during May 1886. One of McKay’s photographs shows the Russian warship Vjestnik anchored in Wellington harbor about two and a half kilometers away, with its rigging lines and gun ports clearly visible. The other, taken from the same point, is of a local hotel, the Shepherds Arms, about 100 metres distant from the camera. The masts of the Vjestnik are visible in the background. McKay's other photographic achievements include photo-micrographs, and a ‘shadow-less technique’ for photographing fossils.

McKay presented his work to to the Wellington Philosophical Society (the precursor of the Royal Society of New Zealand) in 1890.