A lenslet is literally a small

lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...

. The fact that distinguishes it from a small lens is that it is part of a lenslet array. A lenslet array consists of a set of lenslets in the same plane. Each lenslet normally has the same focal length. Lenslets have many uses. One of the key applications for lenslets is in

integral imaging Integral imaging is a three-dimensional imaging technique that captures and reproduces a light field by using a two-dimensional array of microlenses (or lenslets), sometimes called a fly's-eye lens, normally without the aid of a larger overall obje ...

and

light field display Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 ter ...

s. Lenslets are commonly found in

Shack–Hartmann wavefront sensor A Shack–Hartmann (or Hartmann–Shack) wavefront sensor (SHWFS) is an optical instrument used for characterizing an imaging system. It is a wavefront sensor commonly used in adaptive optics systems. It consists of an array of lenses (called l ...

s and beam homogenization optics for projection systems.

References

Lenses {{optics-stub