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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1644666" data-attributes="member: 68323">One other variable for spectacle wearers is the sign and magnitude of their prescription (which can vary between the eyes) and the amount of astigmatism the correction for which will also generate non-circular and non-flat exit pupils.A negative prescription (diverging lens) for a myope actually lengthens the effective ER (Pinewood at -7.5 has reported this effect and even I see it in the -1.5D difference between my eyes. For my Yosemities I see the "extra" ER in one eye over the other. Similarly fo my SEs (and I suspect there might even be making the exit pupil a bit more curved).Hyperopes ("the far sighted") has an even worse problem with their poitive lens shortening ER. Fortunately there are fewer of them than myopes.So that's another point to take into consideration: any additional optics after the eyepiece.</blockquote>