From: stephanie snedden
Subject: Re: 2.5m obslog 20070512 (MJD 54233)
Date: Sun, 13 May 2007 11:50:42 -0600
Curious. The only clue I found was that when you were acquiring the
field, it was transiting, although only at an alt of about 75
degrees. Still, that might be a factor in why you were losing guide
stars (high rot rate) Another factor may have been poor seeing? Some
things to try:
- Do the scale change in small steps (don't move the mirrors too much
at one time) to help avoid losing stars
- Keep your guider exposure times short (10 sec) and let the stars
recenter before doing the next scale change.
- Keep an eye on the size of the rotator errors/corrections.
Steph
On May 13, 2007, at 6:25 AM, doravetz@apo.nmsu.edu wrote:
>
> Cartridge 3, plate 2599, chunk153, Legacy.
> Guide stars found on gotoField after using an offset (guide star in
> fiber 5
> was seen glowing just outside of the fiber's edge).  The Guider
> Data Window
> was asking for percent scale change 0.024 and we could not adjust
> the scale
> without losing guide stars.  We made several attempts and finally
> we skipped
> this cartridge.  Details of the situation are described below.
>
> 04:23Z - Guide stars found on gotoField after using an offset
> (guide star in
> fiber 5 was seen glowing just outside of the fiber's edge).  After
> a scale
> change and focus adjustment only 2 guide stars were present, so
> another
> gotoField was used in attempt to reacquire the field.  Only 2 guide
> stars were
> found again, so we cleared the offsets and issued another
> gotoField.  No guide
> stars were found, so then we tried an fk5 and couldn't locate it
> either.
> Finally, we set the scale back to 1.000000 and then tried an fk5.
> Now the fk5
> star is seen in fiber 10, so we centered it and stickied the
> offsets and
> issued gotoField again.  No guide stars were seen.  We went back to
> the fk5
> and stickied the offsets again (just to make sure).  This time
> guide stars
> were found on gotoField.  When we adjusted the scale according to
> the percent
> scale values given in the Guider Data Window, we lost guide stars,
> and the
> percent scale values increased.  For instance, it was asking for a
> scale
> change of 0.024, so we applied 0.01 and then it asked for 0.04.
> Our several
> attempts to change the scale resulted in scale values subsequently
> larger and
> guide stars lost.  Perhaps Cartridge 3 needs to be checked?  We
> moved to
> Cartridge 4 to see if we experienced similar behavior and we did not.