A diminished image of an object is to be obtained on a screen away from it. This can be achieved by approximately placing:
a convex mirror of suitable focal length
a concave mirror of suitable focal length
a convex lens of focal length less than
a concave lens of suitable focal length.
mage can be formed on the screen if it is real. Real image of reduced size can be formed by a concave mirror or a convex lens.
Let , then
It is given that .
This will be true only when .