Gravitational Lensing
Point-mass gravitational lens: Einstein radius, image positions and magnifications, with a ray diagram and a WebGL schematic.
About this tool
A thin point-mass lens (Schwarzschild deflector) in the weak-deflection limit. Given lens mass M and angular-diameter distances Dl, Ds (with Dls = Ds − Dl in a flat Euclidean approximation), the Einstein angle is
θ_E = √(4GM Dls / (c² Dl Ds))
For a source offset β (here as a multiple of θ_E), the 1D lens equation β = θ − θ_E²/θ yields two images. An extended circular source maps to arcs on the lens plane; when β→0 the arcs become an Einstein ring.
When to use: order-of-magnitude Einstein radii, teaching image parity, arcs, and rings.
Limitations: single point mass; Euclidean Dls; circular source rim sampling; no shear field, no time delays.