# Combination of lens

In the above diagram, let the refractive index of concave lens be $n_1$ and of convex be $n_2$.So in order to apply lens maker formulae for it, will I have to assume air separation between the lens?

What happens if there is another medium between the lens? Will that medium act like another lens because light rays will refract from it like that of a lens?

• Of course it does affect, you can do the math. You can work with $H$ and $H'$ for thick lenses in non-air media. – FGSUZ Oct 24 '17 at 19:05