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Message: <blockquote data-quote="elkcub" data-source="post: 3173785" data-attributes="member: 14473">Hi Kimmo,I don't mean to appear argumentative, or to disparage the personal insights you (Henry, and others) have gained by examining various optical configurations, such as telescope objectives and eyepieces.  However, the impression conveyed is that this is a simple additive process, i.e., an eyepiece without "glaringly faulty" axial aberrations has little or no impact on the combined MTF of the telescope and eye that uses it.  This isn't necessarily correct.  The combined MTF refers to the retinal image the observer's brain uses to judge both the resolution and sharpness of the instrument (the subject of this thread). The best text I know in this area is "Visual Instrumentation, Optical Design and Engineering Principles," by Pantazis Mouroulis (1999).  Pg. 29 is appended because the example in the first paragraph highlights the issue at hand, even for axial effects.  I have to assume that the aberrations in the eyepiece of a well designed birding/terrestrial binocular are engineered to interact with those of the objective, such that the MTF of the combined system is "better" than either component considered separately.  I also imagine that advanced computing capabilities have prompted at least some of the major players to include advanced eye models into their image optimizations.  If that is true, examining such instruments without a valid eye surrogate could be a bit misleading.  Ed</blockquote>

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