A misfigure is a manufacturing error where the curvature or flatness of a mirror or lens departs from the specification. Unlike surface roughness, which causes scattering, a misfigure spans larger spatial frequencies and introduces specific wavefront aberrations like astigmatism or spherical error. It is typically quantified in fractions of a reference wavelength using an interferometer.
Heard on the job
We can't hit a tight focus with this telescope because the primary mirror has a severe misfigure near the outer edge.
Insider tip
A misfigure is usually a permanent polishing error, whereas a temporary distortion caused by a tight mount is called pinching.