A 101 mm -focal-length lens is used to focus an image on the sensor of a camera.
ID: 2309782 • Letter: A
Question
A 101 mm -focal-length lens is used to focus an image on the sensor of a camera. The maximum distance allowed between the lens and the sensor plane is 135 mm .
How far ahead of the sensor should the lens be if the object to be photographed is 11.0 m away?
How far ahead of the sensor should the lens be if the object to be photographed is 3.3 m away?
How far ahead of the sensor should the lens be if the object to be photographed is 1.2 m away?
What is the closest object this lens could photograph sharply?
Explanation / Answer
a) 1/do + 1/di = 1/f
di = do f / (do - f) = (11 * 0.101) / (11 - 0.101)
= 0.102 m
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b) 3.3 m away
di = do f / (do - f) = (3.3 * 0.101) / (3.3 - 0.101)
= 0.104 m
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c) 1.2 m away
di = do f / (do - f) = (1.2 * 0.101) / (1.2 - 0.101)
= 0.110 m
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d) 1/domax + 1/dimax = 1/f
domax = (0.135 * 0.101) / (0.135 - 0.101)
= 0.401 m
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