Thus, the magnification is
m
fD
=
+

1
(9 39)
Since D is about 25 cm, to have a magnification of six, one needs a convex
lens of focal length, f = 5 cm Note that m = h¢/h where h is the size of the object and h¢ the size of
the image This is also the ratio of the angle subtended by the image
to that subtended by the object, if placed at D for comfortable viewing