Santa Barbara Instrument Group CCD Camera Operating Manual

Contents

Santa Barbara Instrument Group CCD Camera Operating Manual Manual pdf 49 page image

Section 8 - GlossaryPage 458. GlossaryAntiblooming Gate - When a CCD pixel has reached its full well capacity, electrons caneffectively spill over into an adjoining pixel. This is referred to as blooming. KodakCCDs with the antiblooming option can be used to help stop or at least reduceblooming when the brighter parts of the image saturate.Astrometry - Astrometry is the study of stellar positions with respect to a given coordinatesystem.Autoguider - All SBIG CCD cameras have auto guiding or "Star Tracker" functions. This isaccomplished by using the telescope drive motors to force a guide star to stay preciselycentered on a single pixel of the CCD array. The camera has four relays to control thedrive corrector system of the telescope. The CCD camera head is installed at the guidescope or off axis guider in place of a guiding eyepiece.CCD - The CCD (Charged Coupled Device) is a flat, two dimensional array of very small lightdetectors referred to as pixels. Each pixel acts like a bucket for electrons. The electronsare created by photons (light) absorbed in the pixel. During an exposure, each pixel fillsup with electrons in proportion to the amount of light entering the pixel. After theexposure is complete, the electron charge buildup in each pixel is measured. When apixel is displayed at the computer screen, its displayed brightness is proportional to thenumber of electrons that had accumulated in the pixel during the exposure.Dark Frame - The user will need to routinely create image files called Dark Frames. A DarkFrame is an image taken completely in the dark. The shutter covers the CCD. DarkFrames are subtracted from normal exposures (light frames) to eliminate fixed patternand dark current noise from the image. Dark Frames must be of the same integrationtime and temperature as the light frame being processed.Dark Noise - Dark Noise or Dark Current is the result of thermally generated electronsbuilding up in the CCD pixels during an exposure. The number of electrons due toDark Noise is related to just two parameters; integration time and temperature of theCCD. The longer the integration time, the greater the dark current buildup. Conversely,the lower the operating temperature, the lower the dark current. This is why the CCD iscooled for long integration times. Dark noise is a mostly repeatable noise source,therefore it can be subtracted from the image by taking a "Dark Frame" exposure andsubtracting it from the light image. This can usually be done with very little loss ofdynamic range.Double Correlated Sampling - Double Correlated Sampling (DCS) is employed to lower thedigitization errors due to residual charge in the readout capacitors. This results in lowerreadout noise.False Color - False Color images are images that have had colors assigned to differentintensities instead of gray levels.FITS Image File Format - The FITS image file format (which stands for Flexible ImageTransport System) is a common format supported by professional astronomical imageprocessing programs such as IRAF and PC Vista. CCDOPS can save image files in thisformat but can not read them..