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A Siemens star, or spoke target, is a device used to test the 
In the field of 
Under optical blur from defocus, a Siemens star (like any periodic pattern) gives rise to the phenomenon of ''spurious resolution'' above the resolution limit, i.e. toward the center of the Siemens star. (Spurious resolution appears similar to aliasing, but it is a purely optical phenomenon, so it occurs without need of pixels.) This results in inverted polarity of the stripe pattern: black stripes appear in the place of white stripes and vice versa (and further polarity inversions occur further inward). (The illustration under Optical transfer function shows spurious resolution caused by blurring.) When looking at the Siemens star with slightly blurred vision, e.g., without spectacles or with defocus from staring, this is seen as a shimmering ring around the Siemens star's center that changes size with viewing distance.
The star was developed by Siemens & Halske AG (today
ISO 15775 chart (pdf)
resolution test chart featuring a vector Siemens star
Siemens star with n=314 sectors for high resolution and easy calculation
(vector graphic in PDF) Visual perception Optical illusions
A Siemens star, or spoke target, is a device used to test the resolution
Resolution(s) may refer to:
Common meanings
* Resolution (debate), the statement which is debated in policy debate
* Resolution (law), a written motion adopted by a deliberative body
* New Year's resolution, a commitment that an individual mak ...
of optical instruments, printers
Printer may refer to:
Technology
* Printer (publishing), a person or a company
* Printer (computing), a hardware device
* Optical printer for motion picture films
People
* Nariman Printer ( fl. c. 1940), Indian journalist and activist
* Jame ...
, and displays. It consists of a pattern of bright "spokes" on a dark background that radiate from a common center and become wider as they get further from it. In concept, the spokes only meet at the exact center of the star – the spokes, and the gaps between them, become narrower the closer to the center one looks, but they never touch except at the center. When printed or displayed on a device with limited resolution, however, the spokes touch at some distance from the center. The smallest gap visible is limited by the smallest dot of ink the printer can produce, making the Siemens star a useful tool for comparing two printers' resolutions (DPI
A Daytona Prototype International (DPi) was a type of sports prototype racing car developed specifically for the International Motor Sports Association's WeatherTech SportsCar Championship, as their top class of car, acting as a direct replacemen ...
). Similarly, it can be applied to a camera
A camera is an Optics, optical instrument that can capture an image. Most cameras can capture 2D images, with some more advanced models being able to capture 3D images. At a basic level, most cameras consist of sealed boxes (the camera body), ...
's optical resolution by taking photographs of a Siemens star printed at high resolution and comparing photographs from different cameras, to see which retained the center detail the closest.
In the field of video production
Video production is the process of producing video content for video. It is the equivalent of filmmaking, but with video recorded either as analog signals on videotape, digitally in video tape or as computer files stored on optical discs, hard dri ...
, where it is often called a back focus chart, the Siemens star is widely used to adjust the back focus of removable lenses. It is also used during film or video shoots to help setting the focus in special situations.
Siemens stars are similar to the sunburst pattern used as a background in graphic design, as in the Japanese Naval Ensign, Russian Air Force
" Air March"
, mascot =
, anniversaries = 12 August
, equipment =
, equipment_label =
, battles =
, decorations =
, bat ...
flag and Jordanian Royal Standard. They are useful in drawing the eye to a point on the page.
Under optical blur from defocus, a Siemens star (like any periodic pattern) gives rise to the phenomenon of ''spurious resolution'' above the resolution limit, i.e. toward the center of the Siemens star. (Spurious resolution appears similar to aliasing, but it is a purely optical phenomenon, so it occurs without need of pixels.) This results in inverted polarity of the stripe pattern: black stripes appear in the place of white stripes and vice versa (and further polarity inversions occur further inward). (The illustration under Optical transfer function shows spurious resolution caused by blurring.) When looking at the Siemens star with slightly blurred vision, e.g., without spectacles or with defocus from staring, this is seen as a shimmering ring around the Siemens star's center that changes size with viewing distance.
The star was developed by Siemens & Halske AG (today Siemens
Siemens AG ( ) is a German multinational conglomerate corporation and the largest industrial manufacturing company in Europe headquartered in Munich with branch offices abroad.
The principal divisions of the corporation are ''Industry'', '' ...
) in the 1930s to test the lenses of Siemens narrow-film cameras.Alexandra Kinter, Siemens AG, Siemens Archives in Munich, Germany.
See also
*Secchi disk
The Secchi disk (or Secchi disc), as created in 1865 by Angelo Secchi, is a plain white, circular disk in diameter used to measure water transparency or turbidity in bodies of water. The disc is mounted on a pole or line, and lowered slowly down ...
References
{{Reflist, 30emExternal links
ISO 15775 chart (pdf)
resolution test chart featuring a vector Siemens star
Siemens star with n=314 sectors for high resolution and easy calculation
(vector graphic in PDF) Visual perception Optical illusions