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Section 8 – Glossary
Readout Noise - Readout noise is associated with errors generated by the actual interrogation
and readout of each of the CCD pixels at the end of an exposure. This is the result of
fixed pattern noise in the CCD, residual charge in the readout capacitors and to a small
extent the noise from the A/D converter and preamplifier.
Resolution Mode - The resolution of a CCD camera is determined by pixel size. Pixel size can
be increased by combining or binning more than one pixel and displaying it as one pixel.
Doing so decreases the effective resolution but speeds up the download time of the
image. Maximum resolution is determined by the size of the individual CCD pixel. The
ST-7XE, 8XE, 9XE, 10XE, ST-10XME and ST-2000XM can run in High, Medium, Low and
Auto resolution modes.
Response Factor - Response Factor is a multiplier used by CCDOPS to calibrate CCDOPS to a
given telescope for photometric calculations. The Response Factor multiplied by 6700 is
the number of photoelectrons generated in the CCD for a 0th magnitude star per second
per square inch of aperture.
Saturation - Saturation refers to the full well capacity of a CCD pixel as well as the maximum
counts available in the A/D converter. The pixel is saturated when the number of
electrons accumulated in the pixel reaches its full well capacity. The A/D is saturated
when the input voltage exceeds the maximum. The saturation values for the various
cameras are shown in the table below.
Full Well
Capacity
Maximum
Electrons
A/D Counts per A/D
count5
ST-5C
50,000 e-
65,535
1.25
ST-237
20,000 e-
4,095
3.4
ST-237A
20,000 e-
65,535
0.7
ST-7XE/ST-8XE9 ABG High Res
50,000 e-
20,000
2.3
Camera
ST-7XE/ST-8XE Med/Low Res
100,000 e-
65,535
2.3
ST-9XE
180,000 e-
65,535
2.8
ST-10XE, ST-10XME
77,000 e-
65,535
1.5
ST-1001E
180,000e-
65,535
2.8
ST-2000XM
45,000e-
65,535
0.72/1.4
TC-211 Tracking CCD
150,000 e-
65,535
1.3
TC-237 Tracking CCD
20,000 e-
65,535
0.72
Sky Background - The sky background illumination or brightness is the number of counts in
the image in areas free of stars or nebulosity and is due to city lights and sky glow.
High levels of sky background can increase the noise in images just like dark current.
For some objects deep sky filters can be used to reduce the sky background level.
5
9
The e-/Count shown are for the High Resolution readout mode. These numbers can be different for other
readout modes. Use the Parameters command in the Display menu to see the actual value for images acquired
in other readout modes.
The non-ABG versions of the ST-7E/8E have twice the full well capacity of the values shown. ABG version may
also vary from camera to camera with maximum counts being as high as ~30,000.
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