Photonics Dictionary: F

The focal length of a lens is the distance between the lens's optical center (or principal point) and the image sensor or film when the lens is focused at infinity. In simple terms, it is the...

A collimator having, at one end of a tube, an objective lens, and at the other, a reticle with a pair of spaced lines located accurately in its focal plane. It is generally useful as an apparatus for...

A device used to measure the focal length of an optical system or lens.

A single-particle scattering technique in which an incident laser beam is tightly focused by means of lenses to yield a focal spot in the scattering material with a diameter on the order of the...

A Fresnel lens is a type of optical lens that consists of a series of concentric grooves or steps carved into a flat, thin piece of transparent material, typically plastic or glass. This design...

In a lens, the square of the radius of its aperture divided by the product of the focal length and the wavelength. It measures the importance of diffraction in the image formed by the lens. A small...