QHYCCD QHY8L - Manual (Page 4)

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exposure time for both frames, the QHY8L uses two exposure modes: Single frame
exposure and double frames exposure. When exposure time is short (high speed
readout mode less than 1.4sec, slow mode less than 3.47 sec), the QHY8L will select
double frames exposure mode automatically. It will expose twice with the same
exposure time. It will readout the first frame pixels after the first exposure, and it will
readout the second frame pixels after the second exposure. But double frames
exposure mode will cause two exposure times. This is not appropriate for long time
exposure. So in long time exposure condition, the QHY8L will use single frame
exposure mode, so the QHY8L will expose only one time. It will keep the first frame
exposure time same with the second exposure time through a special hardware process
in the camera.
Note: In the long exposure time condition, as the first frame has already started to
read the data, and the second is still in exposure, the first frame will produce amplifier
glow. The time is 1.45 seconds or 3.47 seconds. Because the second frame is still
being exposed, the amplifier glow will enter the second frame, so there will be a faint
yellow amplifier glow on the top left corner of the image. The glow must be
compensated through a dark frame calibration.
For 2*2, 4*4 binning modes, the QHY8L chip uses progressive scan mode, so
there is no such problem.
7. About controlling for BLOOMING
The QHY8L CCD chip has -100dB anti-overflow foundation. It is possible to overflow
when you are shooting a very bright target. For the overflow problem of the SONY CCD
chip, you can install mechanical shutter. If you need a mechanical shutter, please
consult QHYCCD or your area dealer.
8. Chip moisture problems.
In certain relative humidity conditions, when the temperature is lower than the dew
point, dew or frost will appear on the surface; this is a law of nature. Ice or dew may
form on the surface of the CCD chip or optical window, and they will impact your
images. If dew or ice forms on the surface of the CCD chip, water can flow onto the
electric board, leading to a short circuit or data corruption. You should not let this
happen.
Chip surface moisture
The internal space of CCD camera is relatively airtight. If dew forms on the surface of
CCD chip, this indicates that there is higher relative humidity in the CCD chamber. You
must dry the chamber using the following method:
• Open the QHY8L in dry place. And put the QHY8L in a dry and airtight
environment for24 hours to make it completely dry.
• Install the QHY8L in the dry environment and seal it.