Caveat 1: I'm not sure if this message should be posted here, or in the Programming forum. Caveat 2: I have a BS in Physics, obtained more than a decade ago, but never actually worked in the field. So I'm a bit rusty. OK, more than a bit. I am writing a program to simulate the trajectory of photons near a black hole - static, no spin, no charge. Mass of black hole is M. Think of it as a raytracer - camera is at a finite distance from black hole, outside the event horizon. Photons are shooting from the camera (opposite from reality - it's the raytracer metaphor), initially shooting at the minimum distance R from the center of the black hole (assuming they move in a straight line), and I need to find out the trajectory of the photons infinitely far past the black hole. Essentially, all I need is the deviation angle, since I'm dealing with the photons at an infinite distance after passing near the black hole. So I guess I need the deviation angle at infinite as a function of M (black hole mass) and R (minimum distance between photon and center of black hole if the photon would move in a straight line ignoring gravity). If there are several ways to calculate this, I need a formula that's simple and cheap from a computational perspective.