JAMB - Physics (1994 - No. 29)
In a projection lantern of focal length f, the object distance u, is such that
u > 2f > f
u < f < 2f
u = f < 2f
f < u < 2f
Giải thích
the object is always located between the optical center of the lens and twice the focal length. or the object is placed at a point between F and 2F to produce a real, enlarged, upright image of the inverted object.