A lens with focal length 50 mm and a maximum aperture f/2 forms an image of an object 9.0 m away.
A. What is the numerical aperture of the lens?
B. If the resolution is limited by diffraction, what is the minimum distance between two points on the object that are barely resolved, and what is the corresponding distance between points?
C. How does the situation change if the lens is "stopped down" to f/6? What is the new numerical aperture? Assume the light has a wavelength of 500 nm for all cases.