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The Maddox rod is a handheld instrument composed of red parallel plano convex cylinder lens, which refracts light rays so that a point source of light is seen as a line or streak of light. [2] Due to the optical properties, the streak of light is seen perpendicular to the axis of the cylinder. [3] Maddox rod and pen torch used in Maddox rod testing
Foucault test setup to measure a mirror. The Foucault knife-edge test is an optical test to accurately measure the shape of concave curved mirrors. It is commonly used by amateur telescope makers for figuring primary mirrors in reflecting telescopes. It uses a relatively simple, inexpensive apparatus compared to other testing techniques.
In 1923 Italian physicist Vasco Ronchi published a description of the eponymous Ronchi test, [1] [2] which is a variation of the Foucault knife-edge test [3] [4] and which uses simple equipment to test the quality of optics, especially concave mirrors. [5] [6]. A "Ronchi tester" consists of: A light source; A diffuser; A Ronchi grating
The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
Fig. 1 illustrates a Twyman–Green interferometer set up to test a lens. Light from a laser is expanded by a diverging lens (not shown), then is collimated into a parallel beam. A convex spherical mirror is positioned so that its center of curvature coincides with the focus of the lens being tested.
A flatness test of a float-glass optical window. By placing a ruler across the image, adjacent to a fringe, and counting how many fringes cross it, the flatness of the surface can be measured along any line. The window has a flatness of 4–6λ (~2100–3100 nm) per inch. An optical flat test in both green and red.
One surface is slightly convex, creating the rings. In white light, the rings are rainbow-colored, because the different wavelengths of each color interfere at different locations. Rainbow-colored Newton's rings on an Agfacolor slide (slightly right of center on the houses and upper right on the mountains).
Like other lenses for vision correction, aspheric lenses can be categorized as convex or concave. Convex aspheric curvatures are used in many presbyopic vari-focal lenses to increase the optical power over part of the lens, aiding in near-pointed tasks such as reading. The reading portion is an aspheric "progressive add".