A light beam parallel to axis is incident on the system of four convex lenses
A,B,C and
D. Focal lengths of
A,B,C and
D are
30 cm,10 cm,30 cm and
10 cm, respectively as shown. Here, fixed distance
BC=20 cm. What should be the distance between the lens
A and lens
D so that after refractions, rays will be parallel to axis in region I, III and V?