# Help me calculate/understand the physics of aperture, DOF and BG blur -

Started 7 months ago | Discussions thread
Re: Help me calculate/understand the physics of aperture, DOF and BG blur -

Dear Bill:

It does have an approximation symbol, but to imply the approximation is related to N requires some proof

Edit: when you reference effective f-number you are speaking of Numerical Aperture (aka working f-number), are you not? Relative f-number (f-number at infinity) is defined by N=f/D according to the previously referenced equations. Can you explain why relative f-number does not relate to DOF? While the calculations might not be perfect it seems pretty clear that the concept is functionally accurate: close iris, smaller entrance pupil, more DOF. Open iris, bigger entrance pupil, less DOF.

If any calculation of DOF must include Pupil Magnification, and Pupil Magnification is defined by Exit Pupil/Entrance Pupil, then any calculation of DOF automatically includes Entrance Pupil.

Again, if you are making the argument that Entrance Pupil cannot be used in any equation that derives absolute DOF, as was stated in your original reply " it's the exit pupil not the entrance pupil", then the burden is on you to show why this is so. Where I'm getting my information is, among other things, mainstream optical engineering textbooks. I’m not saying you’re wrong, but what you said seems to conflict with some of the literature. At least "seems". I don't mean to throw shade, but I think you might've flexed a bit too hard when you contradicted entrance pupil's relation to DOF.

Perhaps it would be of benefit to reproduce the DOF equation you are referring to here, in it's entirety, for the interest of anyone who comes by. I definitely would find it interesting.

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