QHYCCD QHY8L - Manual (Page 9)

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QHY8L CCD Chip Read-out Mode and
Image Calibration.
QHY8L CCD has a 2 channels / 2 frames chip.
There are several things you need to pay
attention to during the shooting and image
process.
The first frame read out the B&Gb pixels, the
second frame read out the R&Gr pixels. When
the 1st frame has exposed done, and it is
reading out, the 2nd frame is keep exposing.
Thus the 2 frames will get a different expose
time. QHY8L uses 2 modes to get the solution.
When the expose time is short (less than 1.45s
for high speed download / 3.47s for low speed
download) , QHY8L will expose twice, and the
expose time are the same. QHY8L will read out
the 1st frame after the 1st expose, and read
out the 2nd frame after the 2nd expose.
However, this mode is not suit for long expose
time. At this time, QHY8L will use another
mode. It take only once expose, and the
special hardware in the QHY8L will compute
the data, for keeping the same expose time
with the 2 frames. The issue is, when QHY8L use the long expose time
mode, after the 1st frame exposes over and it is
reading out, the 2nd frame is exposing. When the 1st
frame is reading out, the AMP light will show, but the
2nd frame is exposing all the same. So the AMP light
will be photoed on the 2nd frame. The AMP light’s
time is about 1.45s(high speed download) , or
3.47s(low speed download) . The AMP light is yellow.
It can be calibrated by taking dark frames.
When using 2*2 or 4*4 mode, QHY8L use the
progressive, so there is no AMP light problem occur.