QHYCCD QHY8L - Manual (Page 20)

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Note: In most cases, there maybe appear some
Vertical stripes in the image which is formed
by lots of BIAS or DARK image stacked.
This is normal. There will not appear such
Vertical stripes after this image is calibrated.
The Calibration Principle of CCD Image
Calibrated image=[(L-B)-(D-B)]/(F-B)=(L-D)/(F-B)
There, L is the actual shooting image, D represents
the Dark Frame images, B represents BIAS image
and F means the FLAT image.
Capture BIAS Image
BIAS image means exposure time of images is Zero.
You need avoiding any light to enter into CCD
Sensor when you shoot image. So you have to
cover the lens cap of camera.
Set Exposure Time to 0, and then use the low
speed to shoot many (10 -50 sheets) BIAS image.
Save and overlap them .Use the function of average
overlapping, do not match with position to get one
BIAS Master image. Save this image.
Partial Cropped BIAS Image（B）
Capture DARK Image
DARK Image means the image which of the
exposure time is the same as the time it took
officially. You have to avoid any light enter into
CCD sensor. Therefore you have to cover the lens
lid.
The exposure time should be set the same with
shooting time .and then use the low speed
and mode 1 * 1 to shoot about (10 -50 sheets)
BIAS image. Save and overlay these images to
form a Dark Master image. Save the image.
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