The image of the United States postage stamps in the figure below is 1.55 times the size of the actual stamps in front of the lens.

Question

Determine the focal length of the lens if the distance from the lens to the stamps is 2.66 cm.

Answer 1

d = 2.66cm; f = 1.55·2.66 = 4.123 cm; 1/F = 1/2.66 + 1/4123; F = 2.66·4.123/(2.66 + 4.123) = 1.617 cm