Re: Mark IV dark images

[hjohnson@pluto.njcc.com (Herbert R Johnson)]

On Sun, 18 Jun 2000 21:34:02 -0500, Tom Droege <droege@wwa.com> wrote:
*>
*>The TECs are still a pain in the neck.  Any shock to the camera is apt to 
*>kill them.  I will no longer glue the TEC stack together.  Just three 
*>grease joints.  I am using vacuum grease (The Dow Corning stuff) which I 
*>fill with silver powder to improve the thermal conductivity.  This seems to 
*>work OK.  This way I can take everything apart to replace one, or to 
*>temporarily remove it while I do something that shocks the camera.  (Like 
*>drilling the extra hole for the out gas flow fitting.)  Some of the TECs 
*>clearly died from my drilling and tapping a hole for the second 1/8 NPT 
*>fitting.

Tom, I'm working on a Tech Note about Mark IV dark images. I'd like to
update it with information obtained from darks from several Mark IV
cameras. I'd appreciate it if you could supply some of the test darks
you are taking from the completed cameras, now that you are in final
assembly and testing. Briefly, I'm tracking some features of the darks
that may be informative about their use.

For instance, some time ago you asked for a "cloud detector" program
to scan a Mark IV image and to "decide" if too much of the field of view
was obscured by poor seeing. Any program to do this would likely need to
also "know" the dark image characteristics of that particular camera at
that time: consequently an analysis of dark behavior is necessary.

You've also mentioned cosmic ray detection; and of course we need darks
for reducing the raw images. I hope my Tech Note will be helpful for
those needs, as well as documenting notes and comments from other TASS
members. The current version is based on Disk #5 darks, some old notes
that I almost "published" some months ago; Disk #15 image information
will be appended to those notes.


Incidently, regarding disk #15 and your imaging schedule: you take a series
of images (pairs of 15 and 150 seconds exposure) followed by a few darks.
Are the dark pairs also 15 and 150 seconds? As no objects are imaged any
exposure differences are not obvious. Dark exposures of equal length to
the image are convenient as they do not require adjustment (multiplication)
before subtraction from the image. I'm writing from memory, but I don't
recall exposure information in the FITS header in your images.

Herb Johnson

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