A camera with a 125 mm focal length lens takes a picture of an object 60 cm long

Question

A camera with a 125 mm focal length lens takes a picture of an object 60 cm long using an f-stop of 2 and time exposure of 1/480 sec.

a) If the film is 24 mm x 36 mm in size, and the image of the 60 cm long object is to fill up the long side of the film (36 mm side), how far away should the object be from the camera?

b) How far should the lens be from the film? (If the distance is close to the focal length, be sure to indicate whether the distance is a little more than or a little less than the focal length.)

Explanation / Answer

As, 1/v + 1/u = 1/f

a) far away should the object be from the camera = (125 * 600)/(600 - 125)

                                                                              = 157.89 mm

b)    far should the lens be from the film = 157.89 * (24/36)

                                                               = 105.26 mm

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