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Principle of CCD camera 

Principle of CCD camera 

Source publication
Technical Report
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Imaging Atmospheric Cherenkov Telescopes (IACTs) are currently the most efficient ground based γ-ray experiments which complement the space based γ-ray detectors in Very High Energy (VHE), E>100Gev region. The overall goal of an IACT is the unambiguous detection of VHE γ-rays from celestial sources. The IACT is a field Instrument in which the detec...

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Context 1
... measurement of the point spread function was performed on Polaris and serius star images with exposures from 0.5 to 5 sec and temperature setting at -10°C. Figure 2 shows the image of serius star acquired by the Central CCD Camera. The image spot is symmetrical, without pronounced substructure, and the width of the spot is well below the PMT pixel size. The image of a star typically spreads over 60 X 60 CCD pixels. The signal charges in the CCD pixels are very high, so that noise and statistical fluctuations in the signal are of no concern. CCD image processing of the point spread function is done using Labwindows Software - where the signal region must be defined without discarding the tails of the intensity distribution. For the determination of the point spread function, the correct removal of the background and the identification of pixels belonging to the light spots are of prime concern. Faint tails of the intensity distribution need to be included without the introduction of a pedestal due to an underestimated background level. In a first step, the spot location is estimated using 5x5 image intensity matrix, where pixels containing maximum intensity matrix has been selected as center of gravity (CG) of the star image. The background level is then determined by applying a Gaussian fit to the distribution of pixel intensities. Because of the good homogeneity of the CCD chip and high Signal to Noise ratio a flat-fielding correction can be omitted. 200 x 200 Pixels image around CG pixel has been used for PSF Analysis. One can see that a point like source is imaged with a finite angular resolution. The image has a Gaussian shape whose standard deviation is also called Point spread function (PSF). There are two effects that much influence the telescope PSF: a) the fact that the mirror is spherical not parabolic, b) the fact that that the surface of the mirror is not a perfect sphere and some light is scattered, c) the fact that the single facet can not be oriented to the center of the camera with infinite precision. In case of vertical incidence, the PSF of the inner half and the outer half of the reflector is similar, meaning that they contribute in a similar way to the quality of the image. This is not true for the outer mirrors in case of tilted ...