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Back to Zeiss    If there was ever made a report of this visit of the IACC in Jena, it must be in french. does anyone know, where it might be found?

Michael Simonsen  Mikedenmark@___ele.dk



Binocular List #266: 23 August 2003


Subject: coloration in optics

From: rab <rab5@___ring.com>

>yellowish hue..... caused from sphero-chromatism in the exit pupil

   I enjoyed your remarks about image coloration in a spotting scope. I had a similar embarrassing experience after I'd been a professional optical designer for 10 years, and had designed a low-distortion microscope eyepiece with a 1mm diameter exit pupil. The hue of the image, as observed with a prototype, depended on how far back the eye was placed, and rendered the design unacceptable. Live and learn!

  The effect you describe can be as complex as spherochromatism of the exit pupil, or as simple as primary color of the exit  pupil. With the tiny exit pupil of a microscope, there's little tolerance for primary color, and that was my problem, but in some low power, wide angle eyepieces, such as the 31mm Nagler,  said eyepiece will show a blue or yellow-brown image hue, mainly around the edge of the field, depending on whether the eye is too close or too far from the nominal pupil. Unfortunately, most designers, especially amateurs, pay little attention to pupil aberration, with the result that, as a rule, only Military optics are properly corrected. Most commercial binoculars have a greater or lesser degree of unpleasantness, depending on the competence and experience of the designer, or cost constraints that preclude doing a first-class job.

  However, the yellow cast found in so many Russian optics is usually due to absorption. You can tell whether the problem is aberration or absorption simply by holding the optic up to the light at arms length, and looking at the color of the exit pupil. Or, if you prefer, laying it, objective down, on a light box and looking at the color coming out of the eyepiece. If it's white, you have a pupil aberration problem. If it's colored, it's absorption.

  Disassembly of a few Russian eyepieces, by Fan Tao, Steve Stayton, and myself, shows that the Russians often used shamelessly yellow glass, as can be seen simply by looking at the edge of the lenses. Check Fan Tao's website for an image of one such disassembled eyepiece   http://binofan.home.att.net/komz.htm   .

  Regards, Dick Buchroeder    (professional optical designer, with one year less experience than your chief design engineer).


Subject: What  to use  for cleaning crud/ polishing etched surface of a 2" coated eyepiece?

From: Tom and Monica Body <plutob@___a>

  I recently picked up in a junkyard a 1970s (?) vintage telescope for directing naval guns, a 10x70 (?) made by Farrand Optical Corp. It  is gyro-stabilized and looks like a small TV set (similar to the Vickers 10x70 on p.414, abb 280 of Seeger's book).   The unit is complete and in excellent shape, except for the outer surface of its 2" coated eyepiece which either has a deposit of crud or has been etched from sitting outside in the junkyard for several years. When I wet the surface of the eyepiece with water or rubbing alcohol, the picture is quite good and you can see the beautiful blue coating, but when it dries, the surface goes opaque and it's like looking through a windshield splattered with mud.

  I've tried all kinds of solvents (Sunlight dishwashing liquid, dishwasher liquid, rubbing alcohol, diluted CLR, acetone, etc) with cotton swab, clean cloth, electric toothbrush, but nothing works: the surface still goes opaque when dry, making it hard to see through.

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