A telecentric lens is a compound lens with an unusual property concerning its geometry of image-forming rays. There are two main types, each with its own use: A lens. ...

1. A lens that is object space telecentric is usually employed for machine vision systems in order to achieve dimensional and geometric invariance of images within a range of different distances from the lens and across the whole field of view.
2. A lens that is image space telecentric is used with image sensors that do not tolerate a wide range of angles of incidence. For example, a 3-CCD color beamsplitter prism assembly works best with a telecentric lens, and many digital image sensors have a minimum of color crosstalk and shading problems when used with telecentric lenses.

An lens is called double telecentric if it is telecentric on both sides. Machine vision (MV) is the application of computer vision to industry and manufacturing. ...

The technical property that distinguishes telecentric lenses is that the chief rays, that is the rays through the center of the entrance or exit pupil, are all parallel to the optical axis, on one or both sides of the lens, no matter what part of the image space or object space they go through.

Object space telecentric lenses

Normal lenses exhibit varying magnification for objects at different distances from the lens. This causes several problems for machine vision and other applications: Magnification is the process of enlarging something only in appearance, not physical size. ...

• the apparent size of objects changes with distance from the camera
• some features or objects may be hidden by objects that are closer to the lens
• the apparent shape of objects varies with distance from the center of the field of view (FOV). Objects appearing close to the edges are viewed from an angle, while objects near the centre of the FOV are viewed frontally (circles near the centre of the FOV become ellipses when moved towards the periphery).

Telecentric lenses, on the other hand, have the same magnification at all distances. An object-space telecentric lens creates images of the same size for objects at any distance and has constant angle of view across the entire field of view. An object that is too close or too far from the lens may still be out of focus, but the resulting blurry image will be the same size as the correctly-focused image would be. A camera is a device used to take pictures (usually photographs), either singly or in sequence, with or without sound recording, such as with video cameras. ...

Because their images have constant magnification and geometry, telecentric lenses are used for metrology applications, when a machine vision system must determine the precise size of objects independently from their position within the FOV and even when their distance is affected my some degree of unknown variations. These lenses are also commonly used in optical lithography, for forming patterns in semiconductor chips. Metrology is variously described as the science of measurement; the science of accuracy and precision; the history of measures; the history of measurement and other definitions. ... Machine vision (MV) is the application of computer vision to industry and manufacturing. ... A semiconductor is a material with an electrical conductivity that is intermediate between that of an insulator and a conductor. ...

Object space telecentric lenses have an entrance pupil infinitely far behind the lens; this is, if you look in the front, the apparent aperture is very far away. In an optical system, the entrance pupil is a virtual aperture that defines the area at the entrance of the system that can accept light. ...

Telecentric lenses tend to be larger, heavier, and more expensive than normal lenses of similar focal length and f-number. This is partly due to the extra components needed to achieve telecentricity, and partly because the object or image lens elements of an object or image-space telecentric lens must be at least as large as the largest object to be photographed or image to be formed. As of 2006, these lenses can range from hundreds to thousands of US dollars or euros, depending on quality. Because of their intended applications, telecentric lenses often have higher resolution and transmit more light than normal photographic lenses. The focal point F and focal length f of a positive lens, a negative lens, a concave mirror, and a convex mirror. ... A 35mm lens set to f/11, as indicated by the white dot above the f-stop scale on the aperture ring In photography the f-number (focal ratio) expresses the diameter of the diaphragm aperture in terms of the effective focal length of the lens. ... 2006 is a common year starting on Sunday of the Gregorian calendar. ... The United States dollar is the official currency of the United States. ... The euro (plural euro--but note linguistic issues concerning the euro, symbol: €; banking code: EUR) is the official currency of the European Union and single currency for over 300 million Europeans in the following twelve European Union member states: Austria, Belgium, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands... Resolving power is the ability of a microscope or telescope to measure the angular separation of images that are close together. ...

In order to optimize the telecentric effect, these lenses are often used in conjunction with telecentric illuminators, which produce a parallel light flow, often from LED sources. Blue, green and red LEDs. ...

Image space telecentric lenses

An image-space telecentric lens produces images of the same size regardless of the distance between the lens and the film or image sensor. This allows the lens to be focused to different distances without changing the size of the image. Undeveloped Arista black and white film, ISO 125. ... Hello--80. ...

At the film or image sensor, all of the chief rays hit "straight on", or at zero angle of incidence. This property minimizes any angle-of-incidence dependence of the sensor, or of any beam-splitter prism assembly, such as a color separation prism in a three-CCD camera, behind the lens. 3CCD is a term used to describe an imaging system used used by some video camcorders. ...

Image space telecentric lenses have an exit pupil infinitely far in front of the lens; this is, if you look in the back, the apparent aperture is very far away. The exit pupil is a concept in optics, and is defined as the minimum diameter of the light beam leaving an eyepiece though which all of the light from the eyepiece passes. ...

The Olympus Four Thirds System specifies a very distant exit pupil (nearly image side telecentric lenses), to avoid the vignetting and color crosstalk that occur in Bayer pattern image sensors with oblique incident rays. Many lenses that have been specially optimized for digital SLR cameras are nearly telecentric on the image side, and consequently have very small angles of chief ray angles of incidence. This article refers to a Japanese camera maker. ... The Four Thirds System is a standard created by Olympus and Kodak for digital SLR camera design and development. ... An example of vignetting in a photograph. ... In telecommunication, the term crosstalk (XT) has the following meanings: 1. ... The Bayer filter mosaic. ... This article needs to be cleaned up to conform to a higher standard of quality. ...

External links

• Technical description of telecentric effect from Edmund Optics, a manufacturer of telecentric lenses
• Another good explanatory page by Donald Simanek