Hi Mark,

Here's a brief overview of what we'd like you to get for us. First, a
few issues which it would be good to resolve before the night:

1) What is the offset from the 2x8 field centre to the 2x3.5 actual
filtered field centre? Remember, the field centres I've quoted here
are for 2x3.5 centres.

2) Can we guarantee that the fields can be in an East-North pointing
position?  In particular, East should be pointing along the 8' side,
ie along the 3.5' side. If we can't guarantee this, it doesn't matter
much, we reckon; the only danger is that we might pick up a brightish
star we didn't want to (although I've tried to keep bright stars well
away).

3) The guide star situation. It's unclear to me from the manual if (a)
we need to quote these, and (b) how far away they can be. By the
nature of the programme, I've tried to veer away from bright stars
(mag<13); please get back to me if we need one nearby.

4) Best way to focus the telescope, and how often this needs doing
through the night; please see the comments on this below.

5) Do you need me to list standards for you?


Start of night: skyflats, bias frames. Plenty of both, please! Do we
need dark frames? - at a rate of 2e- per pix per hour, I don't think so.

Moon sets at 23.23; move to this project at 23.30 until twilight (ie
6.1 hours).

Focus telescope: see manual/discuss with instrument specialist
regarding best focussing method for imaging. Autofoc sounds OK; MAlign
*may* be better, although I'm slightly worried that it eliminates coma
only at a given rotator angle each time, and we don't want to have to
refocus for each field.

Refocus telescope occasionally (once an hour? ask if necessary).

Use CCD in default mode - dual-amplifier readout, fast readout mode, low gain.

Dither pattern; offsets between fields: 
Dither 1 is at [+0",+0"]
Dither 2 is at [+3.536",+3.536"]
Dither 3 is at [+4.830",-1.294"]
These are real arcsec differences, not RA. In RA, second coordinate will be
.236" /cos(dec).
I've listed them explicitly for you on a separate sheet.

Exposure times: 200sec in first dither; 200sec in second; 200sec in
third. Move 4.5 arcmin away East-West, ie 18"/cos(dec) RA; 200sec x 3 again,
with same dither pattern. Then move many arcmin away, begin the
process again.  In figuring out how many fields overall to request, we
assumed a minute overhead for reading out and small shifting telescope
between dithers, and 2 minutes for major shift to new position; ie 14
min per 2x3.5 field.

If you find you're getting behind, keep checking the airmass charts
for the various fields, and if necessary skip a field in order to keep
the airmass down. But consult with us as and when you do this.

Standards: whenever and whatever you like. Do you want me to tell you which?

End of night: skyflats, bias frames.

[Starfield?
STIS overlap?]