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Message: <blockquote data-quote="Surveyor" data-source="post: 1347555" data-attributes="member: 50720">Hello Ed; Like you, I have these same questions and have had the discussion with several far more experienced star testers than myself. I have gone so far as to take the Promaster, my new favorite guinea pig, and my older favorite guinea pig pair, the 8x32 BA’s, and do star test at short range using three different boosters. I have used a 3x Zeiss, a 8x20 Ultravid (gives the best star test of any of my bins checked so far) and a 10x Barska monocular. The three different tests yield about the same pattern, very minor differences, to keep the same aberration ratio between the barrels. I have searched the web and Harold Richard Suiter’s book, Star Testing Astronomical Telescopes and have yet to find a satisfactory explanation. So far, I have rationalized the situation, maybe totally erroneously, this way. Lets assume we are testing a 8x bino and using an 8x booster. At the eye piece of the bino under test we have an objective image with errors magnified 8 times and a eye piece (unmagnified) error of 1. We apply this image to the objective on the booster and it is passed on the the eye piece again, with the objective errors multiplied by 8 and the eye piece error of the test bino multiplied by 8 giving us a ratio at the eye piece of the booster of 64:8, or the same ratio we started with. As long as the objective ratio is quite a bit larger than the total errors most error can be applied to the objective. As I said, I am just guessing until I can find a definitive answer to the question myself. I hope someone posts an answer or better explanation, as I say, I am still concerned myself. Best,Ron</blockquote>

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