In a macro situation, is there a known function that maps the blur radius as a function of the physical distance from the plane of focus?
I'd expect this function to give near zero (in pixels) at zero distance (say in mm), and grow significantly outside the DOF region. Is there a known form for this function? Is it quadratic?
By blur radius I mean the approximate radius of the disc in pixels a point source at the prescribed distance shows on the sensor, assuming that we have a perfectly circular aperture. Note that I'm looking for the answer specifically in the macro situation. For the thin lens approximation we have for the diameter of the blur circle:
Which I don't think applies in the real lens macro situation.