Working F/# is defined as,W= 1/(2n sinθ) 9.OA, 6
where θ is the real marginal ray angle in image space and n is the index of refraction of image space. The marginal ray is traced at the specified conjugates. Working F/# ignores surface apertures but considers vignetting factors. ~f>2U]F>5
Read the manual,you will learn more.