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Message: <blockquote data-quote="Matt_RTH" data-source="post: 1355752" data-attributes="member: 53715">I was thinking exit pupil could have a key to this but I tried my 7x50 binocular and it too had about 25" that I could measure.  I think the field curvature that Alexis mentions makes sense. The EO is notorious for field curvature, while the SP has a relatively flat field.As I thought about this, and just doing this, I realize one significant element of depth of field is where I focus.  When I focus binoculars, I focus such that my subject just comes into focus. Therefore, it is not in the center of focus.  This means that if it goes just forward or just backwards, depending on where I focused , my DOF will appear narrow while not being so. Matt</blockquote>