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Message: <blockquote data-quote="OPTIC_NUT" data-source="post: 3170624" data-attributes="member: 121951">The prism type...and coatings... are part of the design, just like the lenses.There isn't actually an established design for this prism and that powerand objective.    There aren't fixed sets of 'accepted criteria' because there are tradeoffs and customer preferences vary. The design of the eyepiece and/or flattener/focuser lensis of greater importance than the prisms, usually.  That controls the fieldproperties.    And the mechanical smoothness and precision are connectedtightly to keeping left-right sharpness, and thus 3D and contrast improvement in the cortex.  The design is practically everything need todo the whole optical job.  Even the baffling and blackening along thepath is important.   You can see examples in the 70s-80s of the exact samecollection of lenses and prisms with either stainless precision focusers and lamp-black tunnels or short tunnels, wobbly plastic focuser arms,and semi-gloss interiors instead of  flat black. Just those things makefor a hazier, less vivid view with poor 3D.  The design is anything that counts.You could decorate the outside weirdly or in camo, but the optical pathis what matters.</blockquote>