In a 35 mm single lens reflex camera (SLR)the distance from the lens to the film is varied in order to focus on objects at varying distances.Over what range must a lens of 45 mm focal length vary if the camera is to be able to focus on objects ranging in distance from infinity down to 1.4 m from the camera?
A)1.49 mm
B)1.20 mm
C)4.48 mm
D)5.98 mm
E)2.09 mm

Question

Quizplus · Accepted Answer

The correct answer is A.The range of the lens must be equal to the difference between the distance to the film when the lens is focused on infinity and the distance to the film when the lens is focused on the closest object.When the lens is focused on infinity, the distance to the film is equal to the focal length of the lens, which is 45 mm.When the lens is focused on the closest object, the distance to the film is equal to the sum of the focal length of the lens and the distance from the lens to the object, which is 1.4 m.Therefore, the range of the lens must be equal to 1.4 m - 45 mm = 1.49 mm.

In a 35 Mm Single Lens Reflex Camera (SLR)the Distance