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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1354096" data-attributes="member: 68323">That's an rule of thumb for bins with the same physical size so a higher magnification use objective lens with a lower f/number and will have a lower DOF. The thread deals with that.f/number of the objective is the causal issue.Eyepiece design (or whole system design like including a field flattener can have a effect too ... reducing DOF).DOF has a precise definition too: the range in the object domain whose images have a resolution that equals or exceed the detector.Wikipedia has a decent if camera biased article<a href="http://en.wikipedia.org/wiki/Depth_of_field" target="_blank">http://en.wikipedia.org/wiki/Depth_of_field</a>You can estimate it yourself by focusing on a close (5m?) object and viewing text (license plate or a sign) at some distance (40m or more). AB comparing bins this way easily reviews differences in DOF. Using text for the distant target (or a resolution target!) makes actually seeing the difference in DOF easier.BTW to first approximation using the f/number argument (i.e. assuming the bins are the same length which I don't think they are!) the 8x36 would have a smaller DOF than the 8x32.</blockquote>