Thin convex lens
Bends rays with a thin-lens, paraxial focal-length model. Pulse GDD silently assumes N-BK7 and a diameter-aware sag thickness.
Open in the canvas →In the real world
A thin lens bends light by refraction at its two curved surfaces. In the paraxial approximation — rays close to the optical axis, at small angles — those two refractions collapse into a single relationship between object distance dₒ, image distance dᵢ, and focal length f:
In OpticalSetup
Rather than tracing the thin-lens equation for one axial object point at a time, OpticalSetup applies the equivalent paraxial ray-transfer relation to every individual ray that crosses the lens plane. For a ray crossing at height h from the optical axis with incoming slope u (the ratio of its transverse to axial direction components), the outgoing slope is:
This is genuine paraxial optics, not a hand-wavy "bend toward focus": a beam of parallel rays offset from the axis really does converge at the back focal point, and an object arrow really does form an inverted, magnified, or demagnified image at the position the lens equation predicts. What's missing is everything paraxial theory leaves out by construction — spherical and chromatic aberration, finite lens geometry, and any behavior for rays far from the axis or at large angles. For pulse reporting only, the lens silently assumes N-BK7 and a centre thickness from spherical sag plus 2.5 mm edge thickness. That diameter-aware estimate is typically within about 10% for ordinary plano-convex catalogue singlets; it does not change the traced ray geometry.