Any optical system may be analysed with the step-along system, but it's
really tedious and time consuming. When we worked with a thin lens we
found that we could use the same fundamental paraxial equation we used
for a thin lens if we treated the lens position as the reverence point V
instead of the surface vertex and let the thin lens power be the algebraic
sum of the power of the two lens surfaces. Wouldn't it be wonderful if we
could do the same thing with a thick lens?
Well, we can't. Not quite. But we can come close. Consider the thick lens
shown below.It has thickness t, index n", and surface powers F1 and F2.