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- To: firstname.lastname@example.org
- Subject: Camera Noise
- From: Tom Droege <email@example.com>
- Date: Sat, 24 Oct 1998 18:17:57 -0500
- Delivery-Date: Sat Oct 24 19:25:01 1998
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Well, the best that I can do at the moment is 17 e-. This assumes that my
calibrations are correct, and I have no reason to expect that they are. So
I am building a Norman type flat field box. It is gluing now. All out of
white and black paper and foam board. I will light it with red LEDs,
though I also have green ones, or I could use some of each.
Noise from the electronics is now 4 e- equivalent. This is with the camera
cable disconnected. The preamplifier in the camera head has no reason to
generate the 17 e- equivalent noise, so I must presume that the noise is
coming from the CCD and its amplifier. But it now bottoms out as I reduce
the temperature. I can make long exposures without significant increase in
noise. So it is probably not a light leak.
I have some reason to suspect the calibration. Either that or Lockheed is
conservative and has a much wider dynamic range (more full well electrons)
than they claim. Not much chance of that. ;^)
With the flat field box I should be able to take various length exposures
and figure out the calibration from the fact that the well fills up
linearly with exposure while the noise should go as the SQRT. This assumes
I am cold enough that there is not much contribution from dark current.
This seems to be the case as I can now get to -30 C with the refrigerator.