From: Jon Brinkmann
Date: Wed, 21 Apr 2004 11:47:25 -0600
Subject: Re: Spectro focus once again [was RE: 2.5m obslog 20040419 (MJD 53115)]
Where are the collimator numbers for the late-night focus?
Also, what was adjusted?  Was it only the piston on sp1, as per David's
re-run of the idlspec2d collimate procedure?
> From http://sos.apo.nmsu.edu/logfile-53115.html, Tair = 12.9C for the
> preflight focus check exposures, but by the time Wsigma went out of tolerance,
> Tair = 4.3C, so deltaT = -8.8C.  This is non-trivial but not, I think,
> particularly large for this site.
But it is the spectrograph body temperature that matters, not the air.
The spectrograph bodies are not ventilated or actively cooled.  We use
the PMSS average temperature as an estimate of the body temperature.
Note that sp1 needed to be pistoned in all three actuators.  That
doesn't look like an actuator problem.  Also, there were no reported
problems moving the mirror to obtain focus, which would indicate an
actuator problem.  An actuator coupling problem can't cause a focus
shift.  It will only cause problems moving the mirror.
I suspect that the spectrograph body was warmer than the air at opening
and slowly cooled during the night, eventually requiring recollimation.
I inspected all the bolts that I can check without disassembling actuators.
Everything is tight.  I didn't touch the mirror positions.
Also, you are supposed to be recording temperatures when you do focus
checks as so:
im> caget tpm_TM_PMSSAvg tpm_TM_TelairAvg.VALA
tpm_TM_PMSSAvg                5.48071
tpm_TM_TelairAvg.VALA         6.75
The last time temperatures were recorded in the log was March 24th.
You are also to check the slithead latch pressure on the gauge on sp2 near
the slithead door.  I checked it today.  It was 105 psi.
Jon