9
Miscellaneous Issues:
The primary purpose of this camera for most users will be
detection of cloud cover, both during day and night, but primarily
night, at a remote site. Under massive saturation conditions, such as
the sun in the field of view, a vertical column of saturated pixels will
be seen in the image. This appears to be unavoidable at our shortest
exposure of 50 microseconds. When thin clouds are near the sun it
can blossom out horizontally, and be annoying. We feel that, while
this is cosmetically irritating, it does not compromise the primary
purpose of this device much. The monochrome sensors are more
affected by this due to their approximately 4X greater sensitivity.
There is a vent hole underneath the lens plate to allow the
enclosed space under the dome to ventilate to the outside air. There
may be conditions where fogging can appear inside the dome under
rapidly changing atmospheric conditions but it should dissipate
quickly (within an hour) due to the action of the heater. The heater,
when on, is injecting >4 watts into the lens plate to keep the lens clear
of moisture and also the dome, as the heat rises from the plate. This
power level has worked well here in Santa Barbara, which is really
prone to fog due to the presence of the ocean – we think it will work
well for most users. The heater is seldom needed in the day since the
sun heats up the interior of the dome, but will hurt nothing if left on.
The heater schedule can be set within the software mainly to conserve
power for solar powered installations.
Be sure to ground the case. Do not assume the case is
grounded through your PC RS-232 port. At SBIG we have had many
cameras come in that were destroyed by lightning, but at least 4 times
more than that were not actually struck, but simply in the presence of
high electric fields when lightning is in the area. If the camera is on
your rooftop it becomes a lightning rod unless your installation is
solar powered and has a wireless connection. If it is on a roof, and
you are running an RS-232 cable to your PC, we recommend you use
an RS-232 isolator, such as the B&B Electronics 9SPOP2 (
). It slows your baud rate to 115,200. There may be faster
ones out there, but we are not familiar with them.
Since the KAI-340 CCD used in the AllSky 340 camera is
not cooled, dark frames are required on a regular basis to cancel out
the pattern noise due to hot pixels scattered across the CCD. For this
