Re: Mark IV dark images

[Tom Droege <droege@wwa.com>]

Herb writes:

>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.

This is just not true.  I have answered this question several times 
before.  I cannot imagine that anyone cannot understand what I am doing 
after the great detail with which I have answered this.

Here it is one more time:

There repeat is five sequences of short, long, short, and long.  One of the 
five is made with the shutter closed.  In every respect the dark sequence 
made with the shutter closed is exactly the same as the sequences made with 
the shutter open.  It is in fact made with the same code.  When a dark 
sequence is to be made, I simply skip the open shutter code line.  The 
shutter is still closed (even though it is already closed.)  This preserves 
as much timing as possible.  Note that there is a detailed explanation of 
this in TN-62 along with a code fragment so that you can read it and 
understand exactly what is being done.

Tom Droege





>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
>




>Herb Johnson
>
>Herbert R. Johnson              http://pluto.njcc.com/~hjohnson
>hjohnson@pluto.njcc.com         voice 609-771-1503, New Jersey USA
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