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Re: Camera N6 & cooling

On Tue, 02 May 2000 21:43:08 -0500, Tom Droege <droege@wwa.com> wrote:
*>In my search for the ice, there was the mystery of why the I camera (N6)
*>did not develop ice.  Today I took it apart.  There was no heat sink
*>grease.  I had put on two cameras without heat sink grease to investigate
*>if the crystals were coming from the grease.  I then worked on the V camera
*>and forgot about the I camera being greasless.  It is all in the log book
*>if I had looked.  This is one of the disadvantages of working alone.  Well,
*>I write all this here so you all can remind me, but you seldom do.  So that
*>explains it. 

I would like to know how the change in cooling on this camera affects the
dark current and, more importantly to me, how the dark current is
distributed in the dark frames. Tom, can you compare a dark frame from
this camera before your discovery and one AFTER your discovery? Please
note the temperature of each camera at the time, and of course the
duration of dark exposure (hopefully identical). If you can't do this,
or prefer I do this, then FTP the two dark frames and a text file of
their conditions to the TASS FTP incoming site and I will obtain them.

What I'm looking for is changes in the dark current along the edges of
the image. I have an impression that the temperature is slightly higher
along the edges, which creates a rise in dark current relative to the
center of the frame. This rise amounts to 50 or 100 ADU's as I recall
in a general way, but it is different between cameras. This rise has
been discussed casually, but I don't think it has been called out as
a potential temperature shift except by me. A camera that has been modified
to more efficiently cool the CCD would presumably show a more uniform
distribution of dark current. I'd like to find out.

Herb JOhnson

Herbert R. Johnson              http://pluto.njcc.com/~hjohnson
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