Simple lens
In optics, a simple lens or singlet lens is a lens consisting of a single simple element. Typical examples include a magnifying glass or a lens in a pair of simple reading glasses.
Simple lenses are prone to aberration in [optical systems|aberrations], especially chromatic aberration. They cannot be used for precise imaging and make poor camera lenses. They are commonly used for laser applications, however, where the beams are both monochromatic and narrow.
Some cameras with Focus [free lens|fixed lenses] have been made using a simple lens, usually a meniscus lens with the convex face facing outward. In such examples the lens aperture is made small and in some cases, the film plane is curved to reduce the impact of aberrations.