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Message: <blockquote data-quote="ronh" data-source="post: 1535929" data-attributes="member: 55514">Ed, That is interesting what you say about the eye's CA always being there, even if the bino is free from the defect. When telescope and bino users describe the "improvement" in the view when the optics are freed from color aberration, a few notice no difference. Most people notice no difference under normal lighting conditions, and report only a reduction in "fringes", not an improvement in "sharpness" in harsh contrast situations. So I believe you may be right: the CA in the eye, although not obvious thanks to the filtering action of the brain, is dominant. Hope I got that right.I'll give an example of what I'm talking about, the low light extreme, which I am fairly familiar with from many unsuccessful owl hunting adventures. In very low light the eye opens up all the way, and becomes a fast little camera. Most of the  aperture of the binocular comes into play also, because the eye pupil isn't stopping down the exit pupil much, if at all. The bino-eye becomes a relatively fast system, compared to what happens in good light, due to the action of the iris. So, DOF would be predicted, from photography-based equations I have used and basically believe, to be poor.In fact if the light is very low, visual acuity is poor, so that one cannot tell if the binocular is precisely focused or not. It's just too dark to see well. Everything is a dim blur, and objects near and far are seen about as as well as objects "in focus", ie, not well at all. DOF is excellent, but (and because), acuity is terrible.Here I am, belaboring my obtuse point. Do not read the previous two paragraphs, it might not be worth the effort!Ron</blockquote>

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