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Message: <blockquote data-quote="iporali" data-source="post: 1641870" data-attributes="member: 2925">Thanks Henry,You are right that adding all the variables in the equation make this even more complicated. I don't know (yet) how the exit pupil curvature changes during zooming, but I felt that having the eyecup all the way down I can view very easily at 25x (with glasses) and to some extent less easily at 50x with its whopping AFOV and slightly shorter ER - in the middle this eyepiece is still easier (for me) than any other zoom.The main point might be that if the ER is measured at the narrowest point of exiting light cone, the eye pupil may have to be set slightly closer. If the eyecup adjustment is not enough for that (which it should be), the only solution left is to try to avoid black-outs by adapting the viewing style. I am sure there are many, who can do it all instinctively and my instructions just confuse them - apologies to them. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />Best regards,Ilkka</blockquote>