Meniscus corrector
![Albert Bouwers 1941 catadioptric telescope with a concentric meniscus corrector](/Images/godic/202501/26/Bouwers_meniscus_telescope_concentric.svg0512.png")
A meniscus corrector is a negative meniscus lens that is used to correct spherical aberration in image-forming optical systems such as catadioptric telescopes. It works by having the equal but opposite spherical aberration of the objective it is designed to correct (usually a spherical mirror).