Recent content by HIB

Thanks TSny. You have a point about not using the focal length as the object distance. If I approach it from the other side i.e. flat surface first, followed by half sphere surface. Rays are approaching parallel, so s0=∞, surface is flat, so R = ∞ nm/∞ + nl/s1 = nl-nm/∞ nl/s1=0 →s1=∞...

OK... I think I figured this out. I am only taking the refraction from one spherical surface. I am treating it as if the rays are focusing inside the lens. If I take the result of the first calc i.e. f=Rnl/nl-nm and use it as the object distance for the second surface. And bear in mind...

Any help much appreciated - this is driving me crazy! Homework Statement Show that the focal length of a half ball lens, in air, (in the paraxial limit) is given by: f=R/n-1 Homework Equations Equation (from Hecht- Optics), for refraction at a spherical interface: nm/s0 + nl/s1...