Very long-focus lenses may require the camera to be fitted with special extra-long rails and bellows.
Telephoto Lens A specific type of long-focus lens in which a positive (converging) lens element is placed in front of the diaphragm and a negative (diverging) lens element is placed at the rear of the diaphragm.
A long-focus lens brings far subjects closer, like a telescope. They therefore have a smaller angle of view than a normal or wide-angle lens.
or unintentionally by inappropriate equipment, such as unsuitable lens hood or badly designed lens. A common fault of wide-angle lenses, owing to reflection cut-off, etc. of some of the very oblique rays. May be caused in some long-focus lenses by ...
 See also: Focus, Lenses, Speed, Focal length, Zoom
  
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