Open Meeting with Chris Stubbs from Univ. of Washington

On May 9th 1996, Chris Stubbs from the University of Washington held an open meeting for all at Chicago to discuss the present working status of the ARC 3.5m Telescope. Chris begun the meeting by composing a list of problems associated with the whole 3.5m setup including telescope, instruments and future plans. The problems he gave are summaries below and make for interesting reading (notes kindly provided by Luisa Rebull).


optics gives 0.5-0.6'', secondary probably limiting factor.

Primary suppory servo system gives 0.2-0.6'' (function of zenith

20,000 Hz oscillation in elevation control gives 0.2''.

Wind driven oscillations of the secondary (put back to wind if
you can).

Best seeing is in calm weather pointing straight up; 0.7''.
Generally, 1.3'' to 1.8'' from night logs. However, probably
need better monitoring of this. To fix these problems will
likely be expensive and long-term.


Progress made on this. However, still need to rotate instrument
to get guide star into the guider field-of-view (not ideal for
spectroscopy).  Guider has 0.14'' per pixel, thus restricting
it's field-of-view.

Can not guide easily with DSC because the DSC baffle needs to be
removed which increases scattered light.

Would like to guide independent of instrument setup.  Hope to
make further improvements in the next 6 months, The guider has
been given the highest priority.


The 3.5m suffers from scattered light. Present baffling is
inadequent for the job. This issue will probably take a back
seat compared to the above troubles


Concerns about the overall telescope throughput.

Recent problems with the focus. Several users have noticed
radical jumps in the focus of the telescope (even after focus
frames have been taken). Need to re-focus many times a night
which becomes very restrictive. Heidi Newberg recently noted
that the focus changed by 2'' in 40 mins.

Tertiary mirror will undoubtably needed soon as new instruments



This instrument has been much improved over the last year, after
a visit to the mountain by the Princeton group.  However, recent
measuremnents of the throughput of DIS appear to indicate that
it is not as efficient as hoped. {Ledlow recently circulated a
document detailing the throughput of DIS and claimed it had a
peak of 9% in the blue and 8% in the red; these are a factor of
2 less than previous measurements.}

The DIS has a horrible red chip. The DIS blue end still has zero
throughput below 4000A.

The rotational-dependent DIS flatfields are still present due to
the scattered light off the tertiary mirror


The overall setup of this instrument is not stable.


What are the future instruments? Evolution of enterprise.
Estimated 1 million per instruments. How do we secure the
resources for these new projects?

Two forthcoming projects are a 8k by 8k imager built by Chris
Stubbs and the adaptive optics from Ed Kibblewhite.


After he presented this table, the meeting switched to a more free-flowing format with many observers expressing their opinions on the present status of the ARC. Overall, it was clear that the 3.5m was not working to its full potential and this was hindering science from this telescope.

It also became clear that observers within the same institute and between institutes were not sharing information and experiences. The lack of these communication lines obviously reduced the efficiency of everyone since each observer had to tackle the same problems individually with no prior knownledge. To rectify this locally, it was suggested that we have weekly/monthly meetings of observers to share our experiences. Furthermore, we hope this web site will aid in this ambition. For example, the last UC observer on the telescope could post a report to this web site.

Finally, Chris Stubbs aksed for help in tackling the ARC problems. It was clear that too much was being demanded of a small group of people and their resources were being stretched. The range and depth of the deficiencies in the 3.5m needed a large base of people willing to solve particular problems. On a positive note, several people indicated that they would be happy to volunteer their time to help. In particular a large group of UC graduate students (led by Gordon Richards) expressed their interest in helping out. If anyone is willing to help, please contact Chris directly ( with your offer (especially offers to help on particular problems highlighted in the above table).

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last modified 13th May 1996

Any opinions expressed on this page have nothing to do with the University of Chicago or the Department of Astronomy and Astrophysics.