|1. simple camera with meniscus lens, 2. achromatic meniscus lens (Image rights)|
A positive meniscus lens has two spherical surfaces. The name comes from the Greek μηνίσκος meaning a little crescent moon.
It is a convex-concave lens and is thicker at the center than at the edges.
Many simple cameras, for instance the Kodak Instamatic 100, use a single fixed meniscus lens.
It is used to minimize spherical aberration. When combined with another lens, it will shorten the focal length, and increase the numerical aperture (NA) of the system. This increases image resolution and decreases distortion.