Ross Xpres

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The Xpres is a very successful lens made by the British maker Ross. It was introduced as an f/4.5 lens, in about 1914.[1][2] This may be described as a modified triplet, similar to the Tessar[3], except that whereas in the Tessar the rear group is a cemented pair of elements, the rear group of the Xpres is three glass elements cemented together. This was potentially an improvement on the Tessar design.[4] The catalogue in particular claims very good definition into the margins of the image.[2] Ross held licenses for some Zeiss patents, and made Tessars for sale in Britain and its Empire at the time (it is listed as the Ross-Zeiss Tessar in the 1912 and 1914 catalogues); after 1914, it must have been a great advantage to be able to offer the Xpres as a British lens of equivalent quality.

Ross later used the Xpres name for other lenses of very different design. Japanese collector 'ksmt' shows two different varieties, both from around 1936: a 75 mm f/1.9 Xpres[5] of double-Gauss design (i.e. near-symmetrical: each half comprising a single element and a cemented doublet), and a 6½ inch f/2.9 Xpres[6] of a design similar to the Voigtländer Dynar (front and rear cemented-doublet groups, and a central negative element)


Notes

  1. The Xpres is not listed in the 1912 Ross catalogue at Ciné-Ressources.
  2. 2.0 2.1 The 1914 Ross catalogue, also at Ciné-Ressources, describes the Xpres as a new product.
  3. That is to say, it is easiest to describe a Tessar by describing how it differs from a simple triplet, rather than implying any particular design process; Kingslake, Rudolph, A History of the Photographic Lens (1989). "It is certain that the Tessar was not a modified Cooke Triplet, as the series of steps followed by Dr. Paul Rudolph in going from the Anastigmat to the Tessar are well established, but for some of the later designs it is not always clear whether they should be regarded as modified Tessars or modified Triplets."
  4. Greenleaf, Allen R., Photographic Optics (1950), Macmillan, New York. "The Ross Xpres is a further development of the Tessar construction; the rear component is made up of three glasses instead of two, providing still more possibilities for correction of aberrations."
  5. Brass-barrelled 75 mm f/1.9 Xpres of double-Gauss formula, circa 1936, at Japanese collector ksmt's site.
  6. 6½ inch f/2.9 Xpres of Dynar formula, in a sunken mount, at Japanese collector ksmt's site.

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