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Message: <blockquote data-quote="kabsetz" data-source="post: 3172232" data-attributes="member: 10167">Henry and David know this, but for many readers of this thread the following elaboration might be useful.When looking at the highly illustrative figure Henry provided, we should keep in mind that it still shows a simplified scenario where there is only one aberration, SA, present to degrade the image. Aberrations stack, so the end result will be the sum of all aberrations, not just the limit set by the worst one. With even very high quality telescopes, there are often small amounts of other aberrations present in addition to SA, and with binoculars there practically always are, sometimes quite severe. Most common of these are miscollimation (de-centring of optical elements within a single binocular barrel) and, in roof prism binoculars, astigmatism-type light scatter from a prism roof edge that is not precise enough.The presence of additional aberrations will make the MTF curves distinctly worse than the ones in this graph, and unlike SA which does improve with reduced eye pupil, they tend to be constant across pupil diameters.One aberration that people usually tend to forget about when considering what is a "good enough" quality level for binoculars or telescopes is de-focus. We of course try to optimally focus our binoculars on the target, and if we succeed the de-focus aberration is zero for that distance. For any other distance, de-focus sums with the other existing aberrations, and the more of these there are the more precisely does one need to focus and the shallower the effective depth of field becomes.Kimmo</blockquote>

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