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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1386251" data-attributes="member: 68323">Yes.Actually the closer objective of reverse porros make them even more easy to use (i.e. have more overlap) at closer distances (though the downside is they have even less ViewMaster 3D effect).And that's the problem: convergence. Bins do not converge. Or rather most bins ... as Pentax Papillo does converge so it can work at very close focus and distance focus too.All bins with parallel barrels (i.e. all collimated bins) at infinity show 100% overlap. This is just part of "parallel lines converge at infinity".You see overlap because the fields of view overlap. You can draw this out yourself if you draw two triangles at the correct scale for the FOV coming from each barrel. As you go further away from the observer the two barrels overlap more and more. The overlap at infinity doesn't depend on the separation of the objectives but at close distances it makes a big difference. The smaller the separation the objectives the more overlap close up.The overlap at close distance depends upon only two things FOV and objective separation. With a few bins to hand it's easy to verify this.</blockquote>