Thick Lens Paraxial Ray Trace This is an interactive ray trace of a thick or thin lens. The index of refraction, left side radius, incident ray height,and right side radius are adjustable via the sliders at the upper left. To locate the ray that transits the lens requires a quadratic equation solution for the ray height at the right hand lens surface (see link for equations). The thin lens approximation to the focal position is shown along with the ray trace calculation of where the refracted ray crosses the x axis. When the radii of curvature are small, this crossing point varies a lot as the incident ray height is adjusted. This is indicative of the fact that a single thick lens does not have a well defined focus position. Pressing the Start button starts a group of photons along their respective ray paths. These photons continue through the lens (slowing to c/index in the lens) and stop at either the lens axis, if the "Rays Stop at Axis" checkbox is not checked or at a position beyond the thin lens focal position if the box is checked. Some of the photons stop at the outer edges of the lens and this is indicative of the fact that the rays associated with these photons are totally reflected inside and at the right hand surface of the lens.
Click Here for Ray Trace Equations

rL rR index rayHt nRays Rays Stop at Axis Single Step