Question

(a) How far from a 53.6 mm focal-length lens must an object be placed if its image is to be magnified 2.12X and be real?

(b) What if the image is to be virtual and magnified 2.12X?

Answer 1

a) Use the lens equation
1/do + 1/di = 1/f , with di = 2.12 do

1/do + 1/(2.12 do) = 1/53.6
1.4717/do = 1/53.6
do = 78.9 mm

b)Use the same equation, with
di = -2.12 do
1/do -1/(2.12 do) = 1/53.6
0.5283/do = 1/53.6
do = ____ ?