From:    Ted Tarbell 
Date:    Thu Jul 17,  8:05pm
To:      trace_test@sag.space.lockheed.com
Cc:      
Subject: Image Quality from Today's Air Force Target

I have looked at all these AF target images, using exactly the same technique
as I used for the set taken in Palo Alto on July 9.  Both sets are in the UV
quadrant and are very similar.  I have a new version of focus_trace (not
released yet) which measures focus from the innermost groups of tribars on the
AF target; furthermore it can measure focus sharpness either in X & Y as usual
or in +45 and -45 diagonal directions.  It also gives a large blowup on the
screen of the smallest tribars.

Visually, the tribars look as good now as in Palo Alto:  group 6-4 is  well
resolved, and it has a cycle of 2.65 pixels per line pair.  So the telescope is
essentially pixel-limited in the visible, as it should be.

There was some astigmatism obvious in the Palo Alto AF images:  the positions
of best focus for X & Y sharpness were a little different, with Y-focus (ie,
sharpest horizontal bars) coming at higher focus position.  This varied across
the field of view and was worst in the upper left corner.  The upper left had
 with X-focus = 91, Y-focus = 98, +45 focus = 97 and -45 focus = 89.  Today's
AF target images show the same patterns as before in the X/Y and +45/-45 focus
positions across the field, but somewhat less astigmatism.  The upper left is
still (tied for) the worst position, with X-focus = 101, Y-focus = 105, +45
focus = 104, and -45 focus = 102.  This is an extremely small amount--I'm not
sure how many waves it corresponds to but it is way within a
diffraction-limited depth of focus.

I left two postscript files on apache which you locals can print out:

af3_focus_diag and af3_focus_xy

The bottom line is that the telescope is in good shape.  Get the phase
diversity frames tomorrow and I may never ask for any more...

Ted