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Message: <blockquote data-quote="henry link" data-source="post: 1348561" data-attributes="member: 6806">I think the Rons are doing an admirable job here, so I'll just mention one other test I've done a few times to check the integrity of the boosted magnification star-test.Yesterday I star-tested my 92mm Astro-Physics APO refractor, stopped down to 35mm to simulate a small binocular of absurdly high quality. I used both 5mm eyepieces and combinations of low power eyepieces and boosters (25X eyepiece/5x booster and 12.5x eyepiece/10x booster) to achieve about 120-125x magnification. If the booster method adds any significant aberrations they should should be revealed by a visible change in the booster star tests compared to high magnification eyepiece star-tests. In every case the tests looked essentially the same, basically text book perfect, whether using a 5mm eyepiece alone or a combination of low power eyepiece and booster. Real binoculars are nothing like this good. Their aberrations are so large that any tiny addition from the booster will be totally overwhelmed (remember the booster is stopped down and operating at low magnification). I would add that I've never considered this method to be anything other than a necessary substitute for proper star-testing with a high magnification eyepiece, but what else can you do with fixed low magnification binoculars? I wouldn't try to use it to split hairs over wave front errors, but it works fine for revealing gross defects like astigmatism, pinching, coma and defective roof edges.Edit: AP,Yes, I've used all sorts of things for boosters. In the test above I used a 5x25 Takahashi finderscope and a 10x35 Nikon EII. One of my favorites is the Nikon 8-16x40 zoom binocular. Henry</blockquote>

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