^Combing two convex lenses

^Combing two convex lenses

1. Consider a parallel beam of light incident on a combination of two lenses separated by a distance ‘d’ in air or vacuum.

Case (a):

The final beam after refraction from the two lenses becomes parallel if d = f₁ + f₂

Case (b):

The final beam after refraction from the two lenses converges at a point situated in between both the lenses  if d > f₁ + f₂ & (d – f₁) > f₂

Case (c):

The final beam after refraction from the two lenses converges at a point situated outside both the lenses if d < f₁