Collections of Fast WFSC data

Doug's email from 16 January 2009

  It would be useful, but not imperative, to collect some "fast"
wfsc data to try to understand the characteristic of this bad
seeing and why it has such an effect on focus (this is separate
from the preset-double counting).

  "fast" wfsc data means from 1 to 5 second integrations.  The
best would be 1 second integrations, but this will require a
fairly bright guide star.  My estimates of shortest integrations
times for guide star magnitude are:

mag     min integration
>16               30 sec
14>m>16     10 sec
14>m>12      5 sec
<12                1 sec

These are just estimates, so I suggest taking one image at
a given exposure time and making sure the maximum
counts in the Shack-Hartmann spots are greater than
500 (otherwise noise will hurt the analysis) (**Note, IDL
will display the wfsc image, with a scale bar to the side)
To understand this focus problem, 1 sec data would be
best, but 5 second integration data will do fine.

To collect data use the IDL routine agw_wfsc_multiple (Andrew
uses this routine to collect field data).

**Note, collimation loop in GCS MUST!! be off to collect data with IDL
but guiding loop should be running to keep the guide star on the

-> login as LBTO on lbtmu107
-> make a directory for the data and cd there ("%" is shell prompt)
    % mkdir /Repository/AGW_Data/090116w_fast
    % cd /Repository/AGW_Data/090116w_fast
-> determine the current WFSC integration time
    % getStatus
           **Note, getStatus reports exposure time in milliseconds
-> Start IDL   (">" is the idl prompt)
    % idl
    > @wfsc_init
    > agw_wfsc_multiple, 1, EXP=1       (the first image will probably fail to display: bug in my IDL code)
    > agw_wfsc_multiple, 1, EXP=10     (2nd wfsc image will display)
           **Note, 1 is number of exposures to take and EXP=10 is integration time in seconds
-> if exposure time is good then take  at least 30 seconds worth of integration time
         (60 seconds would be better)
    > agw_wfsc_multiple, 6, EXP=10
    > agw_wfsc_multiple, 60, EXP=1
           ***Note, Crtl-c will stop collection of data and leave everything in happy state
    > exit or Ctrl-d
-> when finished set wfsc exposure time back to original (say 30 seconds)
    % setWFSExpTime 30000

Should now be back to original setup and ready to collimate with GCS

**Note, the readout time for a full frame is about 2.5 seconds.  Thus if you are
collecting 60x1 sec frames it will take about 200 seconds

This "fast" data would be useful even when the collimation is not acting funny.  If I had
several sets of 5 second data for a range of seeing value (0.7" to 1.5") I could then
make an estimate of how short of integration time is acceptable in the collimation loop
(eg shorten the integration time to 15 sec so collimation loop is twice as fast)

-- DougMiller - 31 Jan 2009
Topic revision: r1 - 31 Jan 2009, DougMiller
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