Item 5 Part A The picture size on ordinary 35-mm camera film is 24 mm × 36 mm. F

Question

Item 5 Part A The picture size on ordinary 35-mm camera film is 24 mm × 36 mm. Focal lengths of lenses available for 35- mm cameras typically include 28, 35, 50 (the "normal" lens), 85, 100, 135, 200 and 300 mm, among others. Which of these lenses should be used to photograph the following objects, assuming that the object is to fill most of the picture area? a building 240 m tall and 160 m wide at a distance of 600 m Submit My Answers Give Up Part B a mobile home 9.6 m in length at a distance of 40.0 m Submit My Answers Give Up rovide Feedba Continue

Explanation / Answer

A) It depends on whether you wish to use the camera in portrait mode or in landscape mode.
In portrait mode the image must not exceed 36 mm high and 24 mm wide.

Now for objects a long way away from the lens the image is very close to the focal length.

From which we get hi/f = Ho / d
36 / f = 240 / 600
f = 36 * 600 / 240
= 90mm
The closer we get to this without exceeding it the more of the frame is filled by the subject.
So the 85 mm lens is the best choice.
to test hi = f * 240/600 = 85 * 240/600 = 34 mm which fits the length of it and now repeat for the width

hi = f * 160/600 = 85 * 160/ 600 = 22.7 mm which fits within the other dimension.

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B)

Now for objects a long way away from the lens the image is very close to the focal length.

From which we get hi/f = Ho / d
36 / f = 9.6 / 40
f = 36 * 40 / 9.6
= 150mm

The closer we get to this without exceeding it the more of the frame is filled by the subject.
So the 135 mm lens is the best choice.
to test hi = f * 9.6/40 = 135 * 9.6/40 = 32.4 mm which fits the length of it .

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