A 35 mm camera is set up to take a picture of an object with an intensity of I, [W/m²]...The ideal exposure for ISO 400 film results when the camera F-stop is set at F/5.6 using an exposure time of 1/125 sec. Calculate the effective aperture diameter assuming that the camera lens has a focal length of 80 mm. A) the new exposure time required if you change your F-stop to F/4 (this is one F/stop change) while keeping the intensity constant, and B) the new exposure time required if you change your F-stop to F/16 while doubling the intensity.

A 35 mm camera is set up to take a picture of an object with an intensity of I, [W/m²]...The ideal exposure for ISO 400 film results when the camera F-stop is set at F/5.6 using an exposure time of 1/125 sec. Calculate the effective aperture diameter assuming that the camera lens has a focal length of 80 mm. A) the new exposure time required if you change your F-stop to F/4 (this is one F/stop change) while keeping the intensity constant, and B) the new exposure time required if you change your F-stop to F/16 while doubling the intensity.