Question Detail
Question
To improve depth of field, a photographer 'stops down' their camera lens from f/4 to f/8. What adjustment must be made to the shutter speed to maintain the same exposure?
Correct Answer
Option D is the correct answer.
Detailed Explanation
Going from f/4 to f/8 means the f-number doubles. The amount of light admitted is proportional to the square of the aperture diameter, or inversely proportional to the square of the f-number. So, (f/8)² / (f/4)² = (1/8)² / (1/4)² = (1/64) / (1/16) = 1/4. The light entering is reduced by a factor of 4. To maintain the same exposure, the shutter speed (time) must be increased by a factor of 4.
Hint
Remember that the f-number is the ratio of focal length to aperture diameter (f/D). Light intensity depends on the area of the aperture, which is proportional to D².