A lens of greater focal length than a normal lens. Think of the same effect of telescopes or binoculars: a reduced angle of view, and a magnification of what you frame. Normally contrasted with the wideangle lens.

The first and most obvious reason for using a telephoto lens is that you want to take a picture of something small and distant, like a little bird, a naked movie star relaxing in a private beach or some interesting carving on a cathedral spire.

There are are other reasons for using (or not using) a telephoto lens - let me list some (all in comparison to a normal lens):

  1. reduced depth of field: as the lens gets longer, the depth of field becomes smaller, allowing you to exaggerate background fuzzines, and emphasizing the subject. The downside is that it is really easy to take unsharp pictures.
  2. perspective compression: a telephoto lens will give the effect of flattening things. One thing fashion photographers normally want flattened is models' noses (espcially gaunt, anorexic models' noses): that is why they use those monstruous 600 mm lenses.
  3. bulk: despite improvements in design, telephoto lenses are big, heavy, use a lot of glass and are therefore expensive. They look impressive, but are inconvenient as hell, and difficult to use without a tripod.
  4. Working distance: a telephoto forces/allows you maintain a greater working distance from the subject. This can be very good in portraits (because the subject feels less intimidated), in nature photography (because maybe that lion will not eat you) and in fields like industrial photography and photojournalism (do you really want to get close to the drop forge or the riot police ?).
Here are some typical focal lengths in which telephoto lenses are made (this would be for 35mm format):
  • 80 mm: first practical tele, used for portraits.
  • 100 mm: also used for portraits. Typically is between f 1.8 (mega expensive) and f 2.8. Some very nice macro lenses are to be had in this focal distance.
  • 135 mm: an old standby, currently not that popular.
  • 180 mm: this (and the 200 mm) are the last lenses that can be practically used handheld. Nikon makes a very nice 180 mmm f 2.8, with internal focusing and low-dispersion glass.
  • 300 mm: first of the big glass. Exists in f 2.8, much more common in f 4. Here begins the serious wildlife photographer.
  • 400 mm: a popular nature photography lense, made also by many universal (non brand-name) makers.
  • 600 mm: the classic bird lens - birds are small, and easily scared.
The longest tele made is, AFAIK, a 2000 mm f 11 monstruosity produced by Nikon.

Some telephoto lenses, to save on size and weight, employ two mirrors (this is called a catadioptric optical system); they are known as reflex lenses. Fancy telephoto lenses may incorporate an optical image stabilization system.

This writeup was originally a quite irate writeup in answer to another one. The original one having been nuked, I have to rework this into a calmer form.
A telephoto lens is not what you think it is.

There are three major types of lenses:

Likewise, there are three classic lengths of lenses:

  • wideangle (< about 50mm for 35mm format)
  • normal (about 50mm for 35mm format)
  • long (> about 85mm for 35mm format)

Not all long lenses are telephoto.

A telephoto lens is a lens with an opposite design of a retro focus lens. In about 1750 Barlow discovered the principle of a telephoto design. In telephoto design, a diverging lens is placed behind the prime lens. This projects the light to a rear nodal point (where the light converges) that is in front of the main lens (rather than behind the lens with a simple lens). A teleconverter is an example of a telephoto lens attachment.

This design has some advantages and disadvantages. The most obvious disadvantage is the loss of light. There are some issues with the sharpness of the image and a reduced depth of field compared to a non-telephoto lens of the same length. In telephoto design, there is some pincushion distortion. Telephoto lenses have been embraced by the 35mm format providing for more compact lenses (the Canon 400mm f/5.6 lens is only 256mm long). This is especially true in the area of zoom lenses. The telephoto lens has a larger barrel and is heavier (more glass) than a simple lens of the same focal length, but is often easier to work with and hold when it comes to long lenses.

The displacement of the nodal point for the lens causes some issues with various types of photography. When trying to take a panoramic photograph by taking multiple photographs and stitching them together, the rotation should be done about the nodal point of the lens. With symmetrically designed lenses that are focused at infinity, the rear nodal point is always at the true focal length of the lens (may not be the same as what is marked) while telephoto lenses may actual have the rear nodal point in front of the lens.

Large format photography offers cameras that have the ability to shift and tilt the film plane and the lens board. The Scheimpflug principle and the hinge rule work with the lens plane and assume that the the lens is a symmetric design. Placing telephoto lenses or retro focus lenses on a large format camera moves the location of the center of the lens and nodal points making adjustments of the lens plane much more difficult than with a symmetric lens design. They are still useful in cases where the bellow draw is limited (most useful for field cameras). Otherwise, telephoto lenses are large and heavy compared to their standard cousins.

Compare two large format lenses (TS is the telephoto lens):

brand:  model focal max f image  lens to  price
              len.        circle film
Fujinon TS    400mm f/8.0 220    260mm    $1264
Fujinon FS    420mm f/5.6 500    413mm    $642
The telephoto lens of almost the same focal length is:
  • slower
  • casts a smaller image circle - means smaller film
  • requires less distance between lens and film for focusing at infinity
  • is twice as expensive
while the other lens
  • is a full stop faster
  • twice as large of an image is cast
  • has a lens to film distance the same as its focal length
  • is quite reasonably priced (compared to other long large format lenses)


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