Depth-of-Focus Calculator

A cone of light from an f/N lens spreads by 1/N of the distance it travels, so the sensor can move ±N·c from best focus before the blur grows past the circle of confusion c. Depth of focus is 2·N·c. At close range the working f-number N·(1 + m) applies, with magnification m = f / (s − f).

Moving the object from infinity to distance s moves the image back by Δ = f² / (s − f). A fixed-focus module covers infinity to s when Δ ≤ 2·N·c, with the sensor set halfway, Δ/2 behind infinity focus. Tilt budget is atan(N·c / (diagonal/2)): the tilt that alone uses the whole tolerance at the sensor corner. Real budgets split the tolerance between focus, tilt, field curvature and temperature drift, and diffraction adds to the blur at small apertures.