Conjugated thin lens pair
Applies two thin lenses separated by their focal lengths. Each lens uses the same silent N-BK7 sag estimate for pulse GDD.
Open in the canvas →In the real world
An afocal telescope pairs two lenses a distance f₁ + f₂ apart so that parallel rays in produce parallel rays out — no net focusing power, just a change in beam diameter and angular magnification. A Keplerian telescope uses two convex lenses and has a real, inverted intermediate image at the shared focus between them; a Galilean telescope uses a convex objective and a concave eyepiece, stays upright, and needs no space for an intermediate image — the arrangement behind classic opera glasses and compact laser beam expanders.
In OpticalSetup
Two independent lens surfaces, each applying the same paraxial ray-transfer relation, separated by exactly f₁ + f₂ — the afocal spacing shown by the dashed centerline through the icon. Either lens's focal length can be set negative independently, so the same element models both configurations: two positive focal lengths gives a Keplerian telescope with a real crossing point in the middle, while a negative second focal length gives a Galilean telescope that never focuses the beam down to a point at all.
Same paraxial-only physics as a single lens, with no eyepiece field-of-view limits, eye relief, or exit-pupil modeling — just the afocal geometry and magnification. Each of the two zero-thickness surfaces contributes the same silent, diameter-aware N-BK7 sag estimate used by a standalone thin lens, typically a roughly 10% class estimate for pulse GDD.