1. Oct 24, 2004

### tangur

Let's say we have an objet O in front on a glass bead. The first surface will be a convex surface, hence the centre of curvature is in the back of the surface, which gives $$+R_1$$. The object, is a real object in front of the surface, which makes it $$+p_1$$, however for the second refraction, we take $$q_1$$ which becomes $$-p_2$$ + the diameter of the glass bead.Hopefully I have grasped everything right so far, now what I'm not quite so sure about, does surface 2 have its centre of curvature in the back or in the front of the surface. Logically, I'm thinking the center of curvature is inside since the surface 2 is ). Which will give $$-R_2$$.

What I want to be sure to understand, if we have a ) refractice surface, the center of curvature is in front of the surface, and with a ( refracting surface, the center of curvature is in the back of the surface. If i picture the center of curvature as the point were you'd stick the compass in order to make a circle, is that correct?