Calculate compound lens focal length (separated in air by some distance) by using simple optics calculator online.
Simple lenses are subject to the optical aberrations discussed above. In many cases these aberrations can be compensated for to a great extent by using a combination of simple lenses with complementary aberrations. A compound lens is a collection of simple lenses of different shapes and made of materials of different refractive indices, arranged one after the other with a common axis.
Formula:
where,
f1 = Focal length of one of the lenses (m)
f2 = Focal length of the other one of the lenses (m)
d = Distance between the lenses (in air) (m)
f = Compound lens' focal length (m)