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Message: <blockquote data-quote="dalat" data-source="post: 3307770" data-attributes="member: 65207">I'm not an optics geek and not particular keen on learning all about the insides of binoculars, my brain got enough challenge learning about bird IDs and stuff. I got quickly through that Vukobratovich paper anyway, and it is interesting indeed.One thing that caught my attention is the second last parapgraph on page 348. This talks about "spherical aberrations of the exit pupil" that causes the kidney bean effect and that can be corrected by design of the eyepiece.I think it's the first time I read that kidney beaning can be clearly corrected by design choices. And it's quite interesting how users (at least BF members) obsess about certain effects and defects like rolling ball, edge sharpness, etc., but simply accept others like kidney beaning as some sort of mystery abberations that are just there or not, probbably down to individual perception, and not of further relevance when assessing binoculars.The same of course is true for the marketing of the binocular makers. If kidney beaning can be avoided by a certain eyepiece design, why no one touts this advantage?</blockquote>