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Message: <blockquote data-quote="henry link" data-source="post: 1323744" data-attributes="member: 6806">Thanks for the information, Ron. Now I can add another possibility to a growing list of candidates for what causes lateral color in binoculars. A quick check of my homemade lateral color target indicates that covering the lower half of the objective largely eliminates lateral color in the lower half of the field in any binocular, while the upper half is unchanged. It remains something of a mystery to me why binoculars with similar exit pupils and field widths have such different amounts of lateral color, especially near the center of the field. The worst performers can be quite expensive and seem to have a few design traits in common, such as air spaced achromatic objectives, internal focusing elements and possibly roof prisms. Using ED glass in the objective appears to improve things, but does not seem to be a complete fix for binoculars like that, while even very cheap Porros with simple cemented doublet objectives and no focusing element can have very little lateral color except toward the edge where you expect it in the eyepiece.Henry</blockquote>