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CCD Charge clearring, is it required?
I'll raise this issue as a possible concern. I don't know
if it is really a problem. What do the CCD experts think?
Seems to me 40 seconds is a long time for a clear operation.
I've read a few places that you want to do a clear a few times
before each exposure. (Is this true?) If so This adds 80 to
120 seconds of unproductive dead time to the time between
exposures. Maybe we can just take back to back exposures and
I am thinking the a lot of that 40 seconds is taken up by the ADC
delay. I think we could skip this. At least the Mk III driver
does not bother to perform a conversion while clearing. Norman's
Mk III code drives the CCD at maximum rate for about three frames
and never touches the ADC's "start conversion" pin.
I'd like to clear and open the shutter very quickly so as to
minimize the dark current. With a 40 second time to clear,
would a short integration period dark frame contain a "dark
Tom Droege wrote:
> The only way I can see to clear the CCD is to read it out. You
> probably have to do it several times at the start. This seems to
> be a common problem for CCDs. I hear grumbling from the Sloan
> worker bees about this. Each read out takes 40 seconds. You can
> determine when it is done by polling on the memory done bit. Or
> later an interrupt. If it works.
> One does a read out by sending a message to the stamp that says
> "read out the CCD". All the stamp does, is send a single pulse
> to the read out circuitry. It is off and running for the next
> 40 seconds.
--Chris Albertson home: email@example.com
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