A telephoto lens in photography is usually a lens where the focal length is much greater than the size of the sensor or the film plane.  On a full frame camera, the sensor measure 24 x 36mm.  A telephoto lens would be from 100mm. 

Telephoto lenses provide greater magnification of subject.  When looking into the camera, the subject seems to be at a shorter distance than in reality.

Telephoto lenses are particularly well suited to wildlife photography.  In wildlife photography it is often a challenge to be near enough a subject to take a good picture.  Usually, these lenses are heavier than normal and wide-angle lenses.  Recent advances in technology and materials helped reduced the total weight of these lenses though.

Telephoto lens properties

Telephoto lenses have multiple inherent properties that you should take into account when using them.  Here are the most important one:

  • Distance between foreground and background is compressed;
  • Focusing does not allow for object to be near the camera;
  • These lenses are less prone to distortion;
  • On big telephoto lens, a filter holder is near the camera and the filter is inserted into the lens;
  • In order to take sharp picture it is necessary to use a faster shutter speed;
  • Using a telephoto lens for portrait is usually more flattering.

Because of these properties, some scenes/subjects are more suitable than others when using a telephoto lens:

  • Portrait photography;
  • Wildlife photography;
  • Macro photography;

They are less suitable for:

  • Street photography;
  • Real estate interior photography;
  • Group pictures.

Another important aspect of telephoto lenses is their out of focus properties.  As magnification increases in photography, the sharp distance reduces and out of focus area, behind the subject, is less detailed. The forest and clouds in the background of this picture are blurry.  A blurry background is less distracting.

Technical details:

Canon EOS 5D Mark III with 400mm lens at f/5,6