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Astrometric solving or Plate solving or Astrometric calibration of an astronomical image is a technique used in astronomy and applied on celestial images. Solving an image is finding match between the imaged stars and a star catalogue. The solution is a math model describing the corresponding astronomical position of each image pixel. [1]
Angular field of view is typically specified in degrees, while linear field of view is a ratio of lengths. For example, binoculars with a 5.8 degree (angular) field of view might be advertised as having a (linear) field of view of 102 mm per meter. As long as the FOV is less than about 10 degrees or so, the following approximation formulas ...
Imaging of dim celestial targets, usually deep sky objects, requires exposure times of many minutes, particularly when narrowband images are being taken. In order for the resulting image to maintain usable clarity and sharpness during these exposures, the target must be held at the same position within the telescope's field of view during the whole exposure; any apparent motion would cause ...
The plate scale of a telescope connects the angular separation of an object with the linear separation of its image at the focal plane. If focal length is measured in mm, the plate scale in radians per mm is given by angular separation θ and the linear separation of the image at the focal plane s, or by simply the focal length f:
The eye relief of an optical instrument (such as a telescope, a microscope, or binoculars) is the distance from the last surface of an eyepiece within which the user's eye can obtain the full viewing angle. If a viewer's eye is outside this distance, a reduced field of view will be obtained.
E.g. the image contrast and resolution are typically optimal at the center of the image, and deteriorate toward the edges of the field-of-view. When significant variation occurs, the optical transfer function may be calculated for a set of representative positions or colors.
A magnification factor of 10, for example, produces an image as if one were 10 times closer to the object. The amount of magnification depends upon the application the telescopic sight is designed for. Lower magnifications lead to less susceptibility to shaking. A larger magnification leads to a smaller field of view.
The Hubble Space Telescope has three fine guidance sensors (FGSs). Two are used to point and lock the telescope onto the target, and the third can be used for position measurements – also known as astrometry. Because the FGSs are so accurate, they can be used to measure stellar distances and also to investigate binary star systems.