Re: Mark IV dark images

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

On Mon, 19 Jun 2000 13:02:31 -0500, Tom Droege <droege@wwa.com> wrote:
*>Herb and all,
*>
*>As it states in the documentation on disk 15, the only difference between 
*>the darks and sky images is that the shutters are opened for the sky 
*>images.  The procedure is exactly the same.
*>
*>Also per the notes, this does not guarantee that all images are of 
*>comparable length.
*>
*>Tom Droege
*>
*>At 10:48 AM 6/19/00 -0400, you wrote:
*>
*>>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

The notes are slightly ambiguous as to what an "exposure sequence" is.
Tom's sequence is a short exposure, a long exposure, a short exposure,
and a long exposure - four frames. His scheme is to have four of
these sequences, 16 frames or files; and one dark sequence of four
files. But there is no explicit information on the exposure time of
those darks, the 8 I've sampled all look to be of identical but unknown
exposure length. So I will present my data to Tom privately and ask him
to be explicit on the details of these darks, which was my question.

Herb Johnson

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