Difference between revisions of "Telecentric"
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| − | |image_text= 11-inch f/6.8 Telecentric | + | |image_text= 11-inch f/6.8 Telecentric; note that the serial number is not in keeping with<br/>the main sequence suggested by Wilkinson and Glanfield<ref>Wilkinson, M, and C Glanfield. 2001. A Lens Collector's Vade Mecum, CD-rom Version 3F. Edited by A. N. Wright. Cornwall, UK: David Matthews Associates. Chapter 11, Pages 87-88. Cited in the article on [[Ross serial numbers]].</ref> |
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Revision as of 15:25, 15 May 2011
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| Illustration from a Ross advertisement (Image rights) |
The Telecentric is an early telephoto lens made by Ross of London. It was introduced around 1912[1] and was sold until at least 1922.[2] It was replaced with the Teleros soon after this, however.
The Telecentric was made in lengths of 9, 11, 12, 13 and 17 inches, and in maximum apertures f/5.4 and f/6.8. Both of these have the same back focus, which is half the focal length. As can be seen in the illustration, the lens comprises five glass elements in two groups.
Telecentric has come to mean something very specific in optics[3]; telecentric lenses are used in machine vision and measuring applications, but are not of much interest in general photography. The Telecentric is not a telecentric lens.
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| 11-inch f/6.8 Telecentric; note that the serial number is not in keeping with the main sequence suggested by Wilkinson and Glanfield[4] image by Dustin McAmera (Image rights) |
Notes
- ↑ The Telecentric is described as new in the 1912 Ross catalogue at Ciné-Ressources, though not given the same prominence as the Xpres, which is given the front pages of the catalogue, perhaps suggesting the Telecentric was not that new. The 1914 catalogue, also at Ciné-Ressources, still describes the Telecentric as new.
- ↑ The lens still appears in the Ross catalogue The Choice of a Lens, around 1922 (the date December 1922 is given in a price-reduction announcement stuck on the front cover) at Camera Eccentric.
- ↑ Optical measurement techniques with telecentric lenses at Schneider.
- ↑ Wilkinson, M, and C Glanfield. 2001. A Lens Collector's Vade Mecum, CD-rom Version 3F. Edited by A. N. Wright. Cornwall, UK: David Matthews Associates. Chapter 11, Pages 87-88. Cited in the article on Ross serial numbers.
