Halving the focal length of a telephoto lens,while holding aperture size constant,will change the light intensity admitted to the film by what factor?
A) 0.50
B) 2.0
C) 0.25
D) 4.0

Question

Quizplus · Accepted Answer

Halving the focal length while keeping the aperture size constant increases the light intensity by a factor of 4, as the area of the aperture relative to the focal length increases by a factor of 4 (inverse square law).

Halving the Focal Length of a Telephoto Lens,while Holding Aperture