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Message: <blockquote data-quote="kabsetz" data-source="post: 3173971" data-attributes="member: 10167">Hi Ed,I actually like it when you are argumentative, since your arguments are about the topic, are backed up by solid thinking and often, like here, come with references to expert sources.I am well aware of the design principles that Mouroulis mentions in the attached text, and we frequently get to read similar assertions in promotional material for binoculars and spotting scopes. Like you, I used to therefore assume that, like you say, the aberrations in the eyepiece of a well-designed birding/terrestrial binocular (or a spotting scope) are engineered to interact with those of the objective (and prism) so that the combined MTF would be better than for either separately.But, in doing actual tests, I could see over and over again that faults in axial image were the result of the objective/prism system to such a high degree that calling the effects of the eyepiece irrelevant did not seem like an exaggeration. It needs to be kept in mind that in these kinds of optics, the visible faults are a combination of the limits of the design and the limits of tolerances, i.e. how closely does the actual product in your hand match the theoretical design specifications. Usually it is the latter that dominates, to an extent where it becomes very difficult to say much with certainty about the former. Also, if one studies the eyepiece designs used (something Henry has done quite a bit) the conclusion seems to be that almost always just slight modifications of classical designs are used, and very rarely if ever do we see a binocular eyepiece that gives reason to believe that it would be particularly carefully tailored to do something out of the ordinary to the resultant axial image. When it comes to off-axis performance, things are very different and more difficult to test, but here I do believe that optimization is done.Kimmo</blockquote>

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