QHYCCD QHY8L - Manual (Page 12)

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Setting the GAIN and OFFSET
Unlike many other manufacturers, QHYCCD leaves
the the internal settings of the camera ADC GAIN
and OFFSET settings so that you can get the
absolute best performance out of your CCD.
GAIN is the pre-ADC programmable gain amplifier
gain setting, the range is from 0 to 63.
OFFSET is the ADC voltage offset setting.
The correct setting of OFFSET and GAIN can
change the CCD camera system gain, which match
CCD output signal range and scope of the
quantitative ADC to get the best dynamic range.
Usual Calibration Method:
1. Set the Gain=0
2. Set the exposure time to 0 and cover the lens-this
is a BIAS frame .
3. Watch the local average of the captured images
(can use the Noise Analyze function of EZCAP)
4. The ideal average value is around 500 to 1000. If
the value is higher, then you should reduce the
OFFSET. If the value is lower then you should
increase the OFFSET.
5. Repeat steps 2-4 to obtain the ideal OFFSET
value.
6. Open the lens cover and increase the exposure
time. Use a uniform light source, such as light
boxes or an LCD screen, and take a saturated
exposure of the image.
7. Watch the local average value of the captured
images if the value is is less than 60,000, you need
to increase the value of GAIN, if the value is 65535,
then reduce the GAIN .
8.Repeat steps 6-7 to obtain the appropriate GAIN
value.
9.Under the GAIN, repeat steps 2-4, and obtain
more accurate OFFSET。
Note A: For some QHYCCD products when you
use bin modes of 2x2,3x3,4x4, images may
reach 65535 even with gain set to 0.