本题目来源于试卷: Optical Instruments，类别为 IB物理学
[问答题]
When shooting pictures atvq9 ,m ;imam) dw.f+nt very short distances,gct8wsvf1m p6y+t s-y t)u* 6c)udqa9 exposure times must be increased because of the increased distance of the lens from the film for a focused image.
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(a) Show that when the object is so close to the camera that the image height equals the object height, the exposure time must be four times longer (or 2 f-stops) than when the object is a long distance away (say, $$\infty), given the same illumination and f-stop.
(b) Show that if $d_o$ is at least four or five times the focal length f of the lens, the exposure time is increased by less than half an f-stop relative to the same object being a great distance away.
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