A camera takes a perfectly exposed picture when the lens diaphragm is set to f /
ID: 2275568 • Letter: A
Question
A camera takes a perfectly exposed picture when the lens diaphragm is set to f/4 and the shutter speed is 1/250 s.If the diaphragm is changed to f/11, what should the new shutter speed be so that the exposure is still correct? (Standard camera shutter speeds include 1/250 s, 1/125 s, 1/60 s, 1/30 s, and 1/15 s.) A camera takes a perfectly exposed picture when the lens diaphragm is set to f/4 and the shutter speed is 1/250 s. A camera takes a perfectly exposed picture when the lens diaphragm is set to f/4 and the shutter speed is 1/250 s. A camera takes a perfectly exposed picture when the lens diaphragm is set to f/4 and the shutter speed is 1/250 s.
If the diaphragm is changed to f/11, what should the new shutter speed be so that the exposure is still correct? (Standard camera shutter speeds include 1/250 s, 1/125 s, 1/60 s, 1/30 s, and 1/15 s.)
Explanation / Answer
Each step increase in f/stop cuts the amount of light in half, so the shutter speed must double to maintain proper exposure.
Each of these exposures are equivalent:
f/1.4 1/2000
f/2 1/1000
f/2.8 1/500
f/4 1/250
f/5.6 1/125
f/8 1/60
f/11 1/30
f/16 1/15
f/22 1/8
The answer is 1/30th second is the proper exposure at f/11,
if 1/250th second was the right exposure at f/4.
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