BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="elkcub" data-source="post: 3370690" data-attributes="member: 14473">Pretty close.  They are not observing optically defined DOF, which has a very narrow meaning.  They are (in my opinion) reporting on perceived field depth in subjective space.  Some instrument-eye factors that influence subjective field depth are the offset of the objectives (inducing stereopsis), M, FOV and DOF.   Eye factors include involuntary changes in pupil diameter (aperture), accommodative focus, eye movement, and retinal adaptation.  Real world factors are relative inter-object sizes, distances and colors.   From these the brain constructs a spatial 3-D "field," including a depth dimension in which we experience subjective object size, distance, and focus (sharpness).  Reports that objects remain in focus across the subjective field with this binocular and not that one, typically leave instrument differences uncontrolled, such a field curvature, astigmatism and field of view, to say nothing about transmission.  All this said, and without trying to be pessimistic, it's very unlikely that the phrase "depth of field" will ever be limited to the object* domain where it belongs.  * Correction:  According to W. J. Smith, Depth of Field (DOF) refers to object space; Depth of Focus (DOF') refers to image space.  The two are related by the formula: DOF = DOF'/M^2, where M^2 is longitudinal magnification of the system.  Ed</blockquote>