Appendix G: Concepts And Terminology - SBIG STF Series User Manual

Appendix G: Concepts and Terminology

Anti-blooming Gate - When a sensor's pixel has reached its full well capacity,
electrons can effectively spill over into an adjoining pixel. This is referred to as
blooming. Sensors with the anti-blooming option can be used to help stop or at
least reduce blooming when the brighter parts of an image saturate.
Astrometry - Astrometry is the study of stellar positions with respect to a
given coordinate system.
Autoguider - An autoguider a secondary camera that operates alongside the
main imaging camera. Its function is to take a continual stream of short
duration exposures of the sky that contains a suitably bright guide star. These
images are used to monitor if the selected star moves at all. If it does, then
signals are sent to the telescope mount to correct for small drive errors and
long-term pointing drift. This ensures that stars in the main image remain
stationery and perfectly round.
CCD - A CCD (Charged Coupled Device) sensor is a flat, two dimensional array
of very small light detectors referred to as pixels. Each pixel acts like a bucket
for electrons. The electrons are created by photons (light) absorbed in the pixel.
During an exposure, each pixel fills up with electrons in proportion to the
amount of light entering the pixel. After the exposure is complete, the electron
charge for each pixel is shifted one at a time to an amplifier in one corner of
the chip. The resulting voltage is transferred to an external amplifier, filter, and
digital converter. When a pixel is displayed at the computer screen, its
displayed brightness is proportional to the number of electrons that had
accumulated in the pixel during the exposure.
CMOS - A CMOS (Complementary Metal-Oxide Semiconductor) sensor is a flat,
two dimensional array of very small light detectors referred to as pixels. Each
pixel acts like a bucket for electrons. The electrons are created by photons
(light) absorbed in the pixel. During an exposure, each pixel fills up with
electrons in proportion to the amount of light entering the pixel. After the
exposure is complete, the electron charge at each pixel is amplified and
converted to a voltage by a tiny circuit at the pixel. The voltages from each
pixel are read out by built-in digital converters, often with one converter per
column, and the brightness values are read out from the sensor via a high-
speed digital interface. When a pixel is displayed at the computer screen, its
displayed brightness is proportional to the number of electrons that had
accumulated in the pixel during the exposure.
Color imaging with a monochrome camera - One-shot Color (OSC) cameras
with a built-in Bayer matrix are handy for shooting quick color pictures
However, imaging with a monochrome camera provides the best quality,
sensitivity, and resolution.
A filter wheel with appropriate filters is used to create color images using a
monochrome camera. The simplest method is to use three filters, one for Red,
Green and Blue. Once the three images are captured, calibrated, aligned and
stacked, it is very simple to create the color composite image.
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