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Q S I 5 0 0 S E R I E S U S E R G U I D E
26
CCD Ima
section is only intended to be a brief overview of CCDs and CCD Imaging. If you are
there are a number of excellent books that you can use to gain a
we
ging Overview
This
new to CCD imaging
deeper understanding of the issues and techniques. Two very well regarded books that
recommend are:
ƒ The New CCD Astronomy by Ron Wodaski
ƒ The Handbook of Astronomical Image Processing by R. Berry and J. Burnell
How CCDs work
Charge Coupled Devices (CCD) work by converting photons into electrons which are then
stored in individual pixels. A CCD is organized in a 2 dimensional array of pixels. The
used in the QSI 500 Series cameras range from roughly 400,000 pixels (768H x
512W) to 3.2 million pixels (2184H x 1472W).
Each p
Series
c
model trike individual pixels and
are converted to electrons and stored in each pixel well. The effectiveness of this process
referred to as Quantum Efficiency (QE). The number of electrons stored in each pixel
” is proportional to the number of photons that struck that pixel. This linear response is
ptionally well suited to astronomical imaging. A
s
ypes of CCDs
CDs are available in a variety of designs and technologies. QSI 500 Series cameras
mploy two different types of CCDs, Full Frame and Interline Transfer, with numerous
ptional features.
Full-Frame CCDs
Full-Frame CCDs generally provide the highest sensitivity and the widest linear response
range of these two types of CCDs. These characteristics make full-frame CCDs ideally
CCDs
ixel can hold some maximum number of electrons. CCDs used in the QSI 500
can hold from 45,000 to as many as 100,000 electrons depending on the specifi
of CCD. While integrating (exposing) an image, photons s
is
“well
one of the key traits that make CCDs exce
subject that is twice as bright will build up twice as many electrons in the CCD. After an
exposure is complete, the electrons in each pixel are shifted out of the CCD and converted
to a number, indicating how dark or light each particular pixel was. Those brightness value
for each pixel are then stored in the image file, typically a FITS file for astronomical imaging.
T
C
e
o
Section
3