Subject: Re: Minutes of May 11 3.5m User's Committee meeting

From: Karen Gloria

Submitted: Wed, 13 May 1998 16:43:24 -0600 (MDT)

Message number: 278 (previous: 277, next: 279 up: Index)

Just some additional comments on DIS -

Regarding the uneven focus across the DIS red chip, Gene Magnier
noticed it was there in some fields and not in others, suggesting
something moving around inside the instrument, perhaps the imaging
mirror.  I checked the imaging mirror for the red chip while I was in
there changing the gratings and I couldn't get it to budge.  It might
be worth having someone elso look at it, though.  Better to really
rule out the mirror before opening up the camera.  Also, we're still
getting a slightly bimodal distribution of pixel counts in the red
chip bias.  It's quite variable.  I think this needs to be looked at.
I'm concerned that the red chip is going to poop out on us one of
these nights.

Regarding the medium resolution gratings. I did two swaps this week.
Each time it took 2 hours (1/2 hour to physically change the gratings
and 1.5 hours to redetermine the grating zero points).  I expect this
to go down with practice, but don't see it taking any less than 1
hour.  It's not the sort of thing you'd want us to rush.  It'd be
really sad if a grating was dropped because someone was in a hurry to
get on the sky.  So, it really is important to notify us at least a
day in advance (about 1/3 of the time I get filter requests a few
hours before sunset) because the observing specialist will need to
come in an hour or two early that afternoon to swap the gratings.

I'm sorry to hear that some observers didn't get the gratings they
requested.  So far, this week's UW08 run is the first request I've had
to use the medium resolution gratings for science.  So, if users have
been requesting the medium resolution gratings, the message hasn't
been getting through.  Send email to to
let us know about grating requests.

- Karen

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