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Archives of an email list on the history of binoculars. - page 13 / 150





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accessory, so amateurs could make or buy the spherical primary.

  Max used a four-surface Maksutov design by Donald Perry for his 3 inch Ad Astra Maksutovs (and possibly other sizes, for instance the 20 inch Maksutov at Vega-Bray Observatory).  By using a different radius on the secondary "spot", third-order corrections are possible, to improve the performance over, say, the classical Gregory designs using a meniscus corrector (with the reflecting secondary spot on the inside curve).  I believe Bray used a process similar to that used to produce bifocal spectacles to create the differing radius on the secondary spot, grinding and polishing the outer annulus on the inside of the corrector separately from the "spot", which can be thought of as standing "proud" of the rest of the inside curve of the corrector.

  In the prism form, it would evidently be possible to create the effect of a meniscus lens (for the Mak corrector) by forming radii on two of the prism faces, or presumably, a four-surface Mak corrector with an additional radius on the third (reflecting) surface of the prism.  I do not think that he fully pursued the idea, as it would have obviously involved some pretty fancy fixturing to achieve the proper centering of the curves, with no adverse wedge.  Proper centering and other technical production issues are handled using specialized curve generation and polishing machinery, with proper inspection and attention to details.  The costs of tooling up would have to be balanced against the market for such a gadget.  (N.B., usually a lesser consideration in military or aerospace optics production.)

  Max was an expert in this type of optics production -- he specialized in the production of small military optics for many years.  While I have only a small amount of comparative knowledge in the area of optical production techniques, I did visit Bray's shop on E. Pierce St. in Phoenix (this was prior to the Ad Astra firm being sold to Kimball Organ), and I would characterize his manufacturing equipment as modified opthalmic production machinery, probably typical for small lens and prism production, esp. for a small shop.

  So we may state that while optical elements combining curved (as opposed to flat, or "extremely long radius") lens surfaces with a prism are feasible, they have evidently only rarely been made in practice, as you comment.

  There are examples of somewhat larger flat or curved plate "combining glass" elements (also possibly using holographic techniques to simulate lensing) in the "heads up" display sighthead units on modern jet fighters, such as the F-14, F-15, F-16, F-18, etc.  These are used to present a reticle pattern (along with other information) to the pilot, projected at infinity.  The size of these elements is pretty large, so as to project a large enough beam (typically 4 to 6 inches broad) to accommodate the pilot's head movements.  I will defer further comments to Dick Buchroeder, who I believe is an expert on these modern systems.  In my earlier career as an avionics and radar tech,  I maintained and overhauled the somewhat less sophisticated, 1960s era sightheads on the F-105, F-4, and F-104 radar systems, which used a flat combing glass and large, fast doublet lenses for projection of the reticle.

Gene Lucas


(Peter, while these are "mono-optical" systems, the pilot can view with both eyes -- does that qualify as a binocular??  :>))

......they qualify as 'biocular', which is an extremely interesting category of visual instrument design.  Two eyes, one eyepiece.   --Peter


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