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I once read Al Nagler's guide to selecting eyepiece focal length. His recommendation was to get eyepieces that delivered 4mm and 2mm exit pupils for low to moderate power, and 0.5 to 1mm (in a lower focal ratio telescope 0.5 to 0.7 is probably better) exit pupils for high power. And I've pretty much always found that very good advice. The lower power 6 and 5mm exit pupils I have used, but usually with a nebula filter.
So, just multiply your telescope's focal ratio by each exit pupil figure, to get his recommended eyepiece focal lengths - which you can achieve either with individual eyepieces or by Barlowing.
Regards,
Renato
Last edited by Renato1; 21-04-2014 at 12:04 PM.
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