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Message: <blockquote data-quote="typo" data-source="post: 3439306" data-attributes="member: 83808">James,What we commonly see in binoculars is oblique astigmatism. Check out the explaination here. <a href="http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/coma.html" target="_blank">http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/coma.html</a>As you move away from the centre the difference between radial and tangential focus increases. On a point source like stars would appear elliptoid and is penalised by Allbinos. That is consistent with Arek's explaination. I'm sure centre astigmatism does occur but I've not detected it in my testing so far. Nocternal acuity is actualy very poor and it would be quite impossible to spot resolution differences in normal use.I wouldn't question that you and others find the Conquest HD sharp, but the problem we all have is we have absolutely no idea whether that's because the binocular is good or your eyesight isn't good enough to spot it's deficiencies. That goes for professionals too. We need information on either effective resolution or visual acuity (preferably both) to understand the value of such a comment. You would certainly need better than average eyesight to spot the differences I mentioned. David</blockquote>