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Message: <blockquote data-quote="typo" data-source="post: 3440136" data-attributes="member: 83808">Adhoc,Thanks for clarifying that point.Back to collimation.Looking at various articles on line I realised there is another point of potential confusion. The angle made to the objective axis will differ from the angle made to the eyepiece by the magnification and it's not always obvious which the author means. In Bill's article he posted here he refers to the 1977 Ostrovskaya study where "the maximum allowable deviation from parallelism" was 30' dipvergence, 40' divergence and 100' convergence. He states the Navy standard he worked to was 2', 2' and 4'. Seems a curiously large difference. <a href="https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.birdforum.net/attachment.php%3Fattachmentid%3D532327%26d%3D1423719552&ved=0ahUKEwjH4ejtz73OAhXFVxoKHdgAAgkQFggrMAU&usg=AFQjCNHer-yLT34CkSfvlh-D-_mttJbBug&sig2=KDPLyMPIFjhZ8NJOPc8lOg" target="_blank">https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.birdforum.net/attachment.php?attachmentid=532327&d=1423719552&ved=0ahUKEwjH4ejtz73OAhXFVxoKHdgAAgkQFggrMAU&usg=AFQjCNHer-yLT34CkSfvlh-D-_mttJbBug&sig2=KDPLyMPIFjhZ8NJOPc8lOg</a>So was the Navy standard massively over specified? If you look at page 40 of this Tonkin article, for a 10x binocular he gives figures of 1.5', 2' and 4.5' for the real collimation limits which are very similar to Bill's Navy values except he points out that these should be multiplied by the magnification to give the actual tollerances of 15', 20' and 45' or roughly half the Ostrovskaya values.<a href="https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.springer.com/cda/content/document/cda_downloaddocument/9781461474661-c1.pdf%3FSGWID%3D0-0-45-1408011-p175249694&ved=0ahUKEwjH4ejtz73OAhXFVxoKHdgAAgkQFggbMAA&usg=AFQjCNExBeAMlJpA8-1ZIggwJSY9SguzYg&sig2=58wmbY6R_-JumjhXct2eMQ" target="_blank">https://www.google.co.uk/url?sa=t&source=web&rct=j&url=http://www.springer.com/cda/content/document/cda_downloaddocument/9781461474661-c1.pdf?SGWID=0-0-45-1408011-p175249694&ved=0ahUKEwjH4ejtz73OAhXFVxoKHdgAAgkQFggbMAA&usg=AFQjCNExBeAMlJpA8-1ZIggwJSY9SguzYg&sig2=58wmbY6R_-JumjhXct2eMQ</a>It seems to beg the question, was Bill's Navy specification twently fold better than the Ostrovskaya tolerances or two fold?DavidP.S I found a reference to the ISO collimation standard for high quality binoculars in an old post by Surveyor. "Note that ISO 14133-2-2006 for High Performance Instruments shows acceptable edge limits of divergence in the vertical of 20’, divergence in the horizontal of 60’ and convergence of the horizontal of 20’."<a href="http://www.birdforum.net/showpost.php?p=1046458&postcount=7" target="_blank">http://www.birdforum.net/showpost.php?p=1046458&postcount=7</a></blockquote>

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