They are said to have a "virtual focal point ... either convex or concave, which will magnify or reduce, respectively, an image in only one direction. These lenses are often combined with a ...

there was no direct experimental observation of the concave lensing effect, that is, presence of virtual focal plane or demagnified virtual image of an object formed by the plasmonic lens.

"We have fabricated the first negative index concave lens at telecommunications frequencies and with an ultrashort focus," Srinivas Sridhar, a professor at Northeastern University, told optics.org.

Scientists at the University of Birmingham have designed a lens using metamaterials that can function as a convex or a concave lens, according to research published in the journal Nature ...

Mirror is a reflecting surface or a polished metal that forms images ... a virtual image appears to be formed behind the mirror. Mirror is of two types; concave and convex mirror where as lens ...