Angénieux retrofocus

Infobox lens design
scheme = Retrofocus.svg
year = 1931 (cine) 1950 (stills)
author = H. W. Lee of Taylor, Taylor and Hobson (1931) Pierre Angénieux (1950)
elements = 1+(4..5)
aperture = f/|2.5The Angénieux retrofocus photographic lens is a wide-angle lens design that uses an inverted telephoto configuration. The popularity of this lens design made the name retrofocus synonymous with this type of lens. The Angénieux retrofocus for still cameras was introduced in France in 1950 by Pierre Angénieux.

The telephoto lens configuration combines positive and negative lens groups with the positive at the front, so as to reduce the back focal distance of the lens (the distance between the back of the lens and the image plane) to a figure shorter than the focal length. The inverted telephoto configuration does the reverse, employing one or more negative lens groups at the front to increase the back focal distance of the lens – possibly to a figure greater than the focal length – in order to allow for additional optical or mechanical parts to fit behind the lens.

The inverted telephoto design was employed in the early Technicolor "3-strip" cameras since the beam splitter unit behind the lens took up much space, so that a long back focal distance was essential. This 1931 design was by H. W. Lee of Taylor, Taylor and Hobson (British patent no. 355,452). Also, wide-angle lenses for narrow-gauge movie cameras had to be of this type. Since the 35mm single-lens reflex (SLR) requires a space for the reflex mirror, it imposes a limit on the use of wide-angle lenses of normal designs, unless the reflex mirror is locked in the up position. The Retrofocus lenses addressed this situation by making wider lenses usable while retaining normal viewing and focusing.

Made in focal lengths of 24 mm, 28 mm and 35 mm, the Angénieux Retrofocus lens inspired all other lens makers to produce wide-angle lenses of this type for almost every 35mm single-lens reflex, and helped to make it the definitive camera type of the modern period.

References

* cite web
url = http://www.mwclassic.com/articles/agenieux/ageniuex.htm
title = An introduction to Angenieux lenses
author = Paul Gates