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Question 33.9: Shutter speed. To improve the depth of field, you "stop down......

Shutter speed. To improve the depth of field, you “stop down” your camera lens by two f-stops from f / 4 to f / 8. What should you do to the shutter speed to maintain the same exposure?

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The amount of light admitted by the lens is proportional to the area of the lens opening. Reducing the lens opening by two f-stops reduces the diameter by a factor of 2 , and the area by a factor of 4 . To maintain the same exposure, the shutter must be open four times as long. If the shutter speed had been \frac{1}{500} \mathrm{~s}, you would have to increase the exposure time to \frac{1}{125} \mathrm{~s}.

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