A
refracting or
refractor telescope is a type of
optical telescope that uses a
lens as its
objective to form an image (also referred to a
dioptric telescope). The refracting telescope design was originally used in spy glasses and
astronomical telescopes but is also used for
long focus camera lenses. Although large refracting telescopes were very popular in the second half of the 19th century, for most research purposes the refracting telescope has been superseded by the
reflecting telescope which allows larger apertures. A refractor's magnification is calculated by dividing the focal length of the objective lens by that of the eyepiece.