Difference between revisions of "Telecentric"
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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. | 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. | ||
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| + | ''Telecentric'' has come to mean something very specific in optics<ref>[http://www.schneiderkreuznach.com/pdf/div/optical_measurement_techniques_with_telecentric_lenses.pdf ''Optical measurement techniques with telecentric lenses''] at [http://www.schneiderkreuznach.com/ Schneider].</ref>; 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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Revision as of 08:59, 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 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.
