Subject: Placing objects accurately on the slit

From: strauss@astro.Princeton.EDU

Submitted: Mon, 23 Nov 1998 01:13:35 -0500 (EST)

Message number: 69 (previous: 68, next: 70 up: Index)

Hello all,
  The following may be routine procedure for most of you, but let me
warn you of a potential pitfall in placing objects on the slit of DIS
using the slit-viewing camera.  It appears that the edges of the 1.5"
slit are not perfectly reflective, so that the region which is not 
reflected back to the slit-viewing camera is not 1.5" wide, but rather
about 3.4" wide.  As you know, the 3.5m points incredibly well, and
so it does happen that according to the slit-viewing camera, it appears
as if the object is completely swallowed by the slit when you first
slew to it.  However, this can be misleading; it is always better to 
first get a slit image with the object off the slit, and then offset
the telescope to put the object at the center of the slit.  Even if
the object appears to be in the slit, it may not be quite.

  Apologies to all for whom this is standard operating procedure, but
we have lost time to this elementary mistake.

			-Michael Strauss

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