◈ Strong Lensing Simulator

Each perturber is a singular isothermal sphere, α = θ_E,p·(θ−θ_p)/|θ−θ_p|. Drag a dot on the image plane to move it; shift-click to drop a new one. Deflections add linearly, so several deflectors can produce the same image configuration.

Pin the images of one lens model, then change it: move or delete a perturber, add a second one, or click Refit to make the main lens compensate (it fits the bright, μ≥1, images). Hollow rings show the pinned images. The table compares positions (Δθ) and normalised fluxes (f = μ/Σμ). When positions match but fluxes or caustics differ, the two models are degenerate in astrometry alone.

Click/drag on the source plane to move the quasar+host. Lensed images appear on the image plane via ray-tracing.