A concave lens is thinner in the middle than it is at the edges. This causes parallel rays to diverge . They separate, but appear to come from a principle focus on the other side of the lens.

ECOPTIK - Plano Concave Cylindrical LensA plano-concave cylindrical lens is used to expand light in on-axis. A negative cylindrical lens is able to diverge collimated input light away from a line.

The authors of the article “Focusing by Plano-Concave Lens Using Negative Refraction” are Plarenta Vodo, Patanjali Parimi, PhD, Wentao Lu, PhD, and Srinivas Sridhar, PhD, from the department of ...

Lenses - AQA Convex and concave lenses Lenses are precisely shaped pieces of glass that have been developed and used in corrective glasses, telescopes, microscopes, binoculars, and magnifying glasses.