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Changing Things On the Fly

ICE allows you to pause (``p"), resume (``r"), stop (``S") and abort (``A") an exposure in the midst of an integration. Furthermore, you can change the integration time (``x"), or the title (``t") during an exposure. Since each command is a single key-stroke command (no carriage return is needed), accidentally typing in the data acquisition window during an exposure could have serious consequences. (For instance, typing a flpr with the mouse positioned in the acquisition window would pause (``p") and then resume (``r") an exposure!) Thus we require an exposure to be paused before doing anything else, and the commands that terminate an exposure, stop and abort, require capital letters (``S" and ``A").

A Momentary Flutter: How to Pause and Resume an Exposure

  Consider the unlikely situation that clouds have drifted overhead during an exposure. You may wish to close the instrument shutter until that single cloud moves by. To pause the integration simply type p in the acquisition window. (The exposure must be long enough that you are seeing the updating ``Time left" message, i.e., >5 secs.) You will see a ``PAUSED" message printed next to the dewar temperature.

To resume the exposure, simply type an r. The shutter will open and the time will begin updating again.

Terminating an Exposure Early: Stop and Abort

  You may decide to stop an exposure early. First you must pause the exposure using p; you can then type a S to stop. (Note that the ``S" must be upper-case.)

Or you could decide you don't want the current exposure at all. In order to abort the exposure, first pause the exposure with a p and then abort the exposure with an A. The image will be lost, and the exposure counter will not be updated. (Note that the ``A" must be upper-case.)

Changing the Exposure Time

  It is also possible to change the exposure time in ICE. You must first pause the exposure using a p. Once paused, you may change the exposure time by striking the x key. You will be queried for the new exposure time. Don't forget to follow this with an r to resume the exposure.

Note that while you can always shorten the length of an exposure, you can only increase the length of an exposure if the initial exposure length was longer than 5 mins (by default). The user should be warned that an exposure time that has been changed to 30 secs, say, will not be as accurately timed as an exposure that began and ended as 30 secs. This is due to the fact the Unix system, rather than the CCD controller, keeps track of the time if the exposure time is altered. We are uncertain, currently, what sort of error this may introduce; the most pessimistic estimates are 1 or 2 seconds regardless of exposure time. Thus this method should be fine for long exposures, but may be dicey if 1% photometry is needed for short exposures! We recommend not altering the exposure time if 1-2 sec errors in the subsequent timing would affect your results.

Changing the Title

  Once you are paused, you can even change the title of the exposure. (Of course, you are losing valuable observing time while you are exercising this feature!) First type p to pause, and then type t. You will be asked for the new title. Don't forget to resume the exposure with an r.

next previous contents
Next: The Amazing Power of flpr Previous: Doing More with mores
Tue Feb 14 07:48:00 MST 1995