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It may be a somewhat old thread but I was under the impression that the maximum effective aperture of an eyepiece was 7mm(the largest exit pupil) and the effective F/ratio is the F/ratio of the telescope. The Conrody standard says that the F/ratio should be five times the aperture in inches using standard glasses to produce acceptably low amounts of chromatic aberration. For an aperture of 7/25 inch, the F/ratio should be at most F/1.4. How many people observe visually using F/1.4 telescopes? The fastest visual telescope I've heard of is F/2.5. That is well more than the minimum and is an extreme.
Ralph
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