BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="elkcub" data-source="post: 3440767" data-attributes="member: 14473">Hi David,Yes, we certainly agree that the eyes are anatomically more "tolerant" of convergence than divergence, and that the latter should be prevented.  This is accomplished by imposing a minimum 5 arcmin convergence demand on the eyes.  The dipvergence spec of ≤ 5 arcmin is really bidirectional around zero, so the manufacturing range is ± 5 = 10 arcmin.  Military standards are significantly effected by anticipated combat task performance, e.g., enemy aircraft detection, shipboard horizon scanning, long-range tank surveillance, etc., and for that reason don't cater to "relaxed" viewing that a birder might appreciate at shorter distances.  I would imagine that astronomy uses might also be more demanding of parallelism, although I should avoid saying anything about that domain.  In any event, Bill's demanding spec of 4 arcmin probably reflects that kind of military requirement (although I don't recall him stating it).  I have little doubt that mid-priced products are getting better, and will continue to do so.  A big incentive, I suspect, is the prospect of large military contracts, which increasingly favor low bid off-the-shelf products.  Ed</blockquote>