Subject: The DIS Slit Viewer is now required operation

From: Noel Camron Hastings

Submitted: Wed, 31 Jan 2001 20:42:28 -0700

Message number: 487 (previous: 486, next: 488 up: Index)

	Well, the testing phase of the DIS slit viewer is over and it is now in
full operation. This means that if you are a DIS observer, you are now
required to know how to run the slit viewer and maintain stars on the
slit during your runs. It is very simple, and the manual for the camera
can be found at:

	Read the manual, play with the camera. You can log in during the day and
try it if you send <> a message and ask about
it. That, or try <> and someone will give you the
OK to try it. There are basically a few commands to know for sure:

expose <time>
window (makes a subframe)
full (returns chip to full frame)
'C' in the graphic display (to get centroid of object for offsets)
repeat (to start series of exposures)

	There are many other commands, some of which will be quite handy for
different people and situations. Please do not show up and say, "So, how
does this work?" because you will only be wasting your on sky time
figuring it out. Most people that have done that have figured it out in
10-15 mins though.

	One of the biggest problems I have seen so far is that when people get a
slit image, they find the offset needed and then do not know how to
offset the telescope. There is an offset control window under the
'Telescope' menu. There you will want to use 'Instrument' type offsets
and select 'Abs' for absolute mode. Absolute differs from Relative in
that an absolute offset is always a absolute from original telescope
pointing. The numbers required here are in arcsecs and that is the unit
that the slitviewer gives you for offsets as well. The only odd thing is
that the slitviewer gives you 0.01 precision and the offset control only
takes 0.1 precision, so round off.
	Many people do not know the difference between 'Absolute Offsets' and
'Relative Offsets'. We try and use Absolute for various reasons, but the
easiest way to explain is this is this. If you type an offset in of 0.6"
and hit 'Offset' three time, you will get a total offset from your
original pointing of 0.6" in absolute mode and 1.8" in relative. Relative
is always relative to your CURRENT position, so every time you hit 0.6"
it jumps another 0.6" whereas Absolute mode simply think you still mean
0.6 from original pointing.
	Once you have made an offset in Absolute mode you will then need to add
or subtract from what is currently in your offset window to make minor
adjustments. If you offset 4.6" and then decide you need to go to another
0.2" then enter 4.8" and hit offset again. Simple.
	If this does not make sense, please email the observing specialists
before your run to help clarify. The phone is a lot easier than typing
this all out....

  Noel Camron Hastings ~ Apache Point Observatory

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