Subject: 1.5 arcsec slit is not 1.5 arcsec

From: karen@tycho.apo.nmsu.edu

Submitted: Sun, 10 Mar 1996 19:04:32 -0700

Message number: 11 (previous: 10, next: 12 up: Index)

I measured the diameter of the quartz DIS slit on the Solar
Observatory's measuring engine.  I measured the width of the slit at
five points along its length.  Here are the measurements.

width (microns)    width (arcsec)      
    170			1.00
    168			0.99
    177			1.04
    178			1.05
    178			1.05

[the scale at the focal plane is 0.00589 "/micron]

From these measurements the average slit width is 1.03 arcsec,
significantly narrower than the 1.5 arcsec we've been assuming.

I also measured the width of the NMSU 2 arcsec acetate slit.  The
measured width is 2.13 arcsec.

Here are a few words on the appearance of these two slits as viewed
under the microscope.

The quartz slit width is very non-uniform.  The edges are noticably
wavy under the microscope.  There's a ragged notch in the edge at one
location, and there are several small dark spots along the slit.

The acetate slit has very uniform width but the under the microscope
one can see that the "clear" portion of the acetate (the slit) has
thousands of tiny colored flecks (or very tiny bubbles) embedded in
it.

-karen g.

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