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5. Exposure Configuration

5.1 defaults

This is a good command to include at the top of scripts, or when the system is in an unknown state. Note that even if DetCom has just been started from scratch, all previous states and modes are restored from the last known settings, so it is generally a good idea to start by sending defaults to reset things.

The command will reset the filename to a default pattern, select a full raster and a default object exposure time.

5.2 mef on|off

This command selects whether mosaic data should be saved in a sub-directory with one basic FITS file per amplifier, or whether a single Multi-Extension FITS file should be generated with IMAGE extensions for each amplifier.

If the filename currently displayed in the blue status bar contains an asterisk (``*'') then mef mode is off and multiple files will be saved.

5.3 reserve

Versions of DetCom through 3.54 kept a minimum of 100 COMMENT keywords in each primary and each extension header unit of a FITS. These COMMENT lines are intended for downstream programs that wish to add (not modify existing) keywords. The reason for inserting these COMMENT lines is that the libfh FITS library is able to use them to add other keywords to the file after DetCom has closed it without reallocating the whole file. This is just a matter of efficiency, and a limitation of FITS.

As of version 3.56, this default has been raised from 100 to 200, but the reserve command has also been added. To switch back to the previous setting that was used by all DetCom versions through 3.54, use:

> reserve 100

If it is desirable to have DetCom produce FITS files with no space reserved for downstream use, this is also possible now with 3.56, by using the command reserve 0. Since it is only CFHT libfh FITS library, which uses these special reserve COMMENT lines, sites not using that library or adding more keywords downstream may want to use the 0 setting.

The current status of the reserve command is echoed when the command is typed with no parameters, and it is remembered in the .detcomrc file across restarts.

Ideas exist to make future versions of DetCom collect arbitrary keywords from the Status Server shared namespace which could eliminate the problem of needing to guess or calculate how much extra space to leave.

5.4 header

The valid choices for the first argument of this command are comment, observer, and object followed by arbitrary text to be inserted into the corresponding keyword in the FITS header.

The arguments _runid, and _piname (note leading underscore) are also accepted.

5.5 nheader

This command takes four arguments, and can be used to add or change arbitrary keywords that will appear in all FITS data. The first argument is a sorting number which controls where in the header the keyword will appear. These sorting numbers must be chosen relative to the ones DetCom uses internally for the keywords it generates. (See det_data.c.) A negative sorting number means the keyword will appear in the next FITS file saved (only) while positive sorting numbers cause the keyword to be added until an nheader reset command is issued.

The second, third, and fourth arguments specify the keyword name (up to eight letters), the contents of the keyword formatted as it should appear in the FITS header, and a comment to be placed after the slash ('/') character in the keyword line.

Many sites have strict requirements about FITS header formatting, and may not wish to have general users sending the nheader command.

5.6 raster

All systems accept raster full which selects the maximum number of pixels available. The other options to the raster command are system-specific, and the command raster help will list other options currently available for your system.

5.7 etype

A single parameter must be supplied selecting one of the following exposure types: ``object'', ``dark'', ``bias'', ``focus'', or ``flat''. Note that some systems may implement other higher level exposure types, implemented as director scripts, which involve interaction with other subsystems such as telescope and/or instrument control. An example of how this is done for the CFH12K should be added here, in this manual.

The current etype will be stored in the FITS headers of subsequent exposures, but also sets everything needed for the current exposure type mode affecting the telescope, instrument, and detector control.

5.8 etime

Accepts a single parameter giving the ``exposure'' time in seconds. If etype dark is selected, this value is the integration time with the detector shutter closed, and if etype bias is selected, this value is ignored, but must still be left set to a value in the valid range of the detector system. Values can either be in format (minutes:seconds.fraction) or just in seconds. The range of legal values and the resolution depend on the detector system in use.

etime 600
etime 10:00

These commands are equivalent. Both select a 10 minute exposure.

next up previous contents
Next: 6. Starting and Up: DetCom Detector Control Previous: 4. Engineering Commands   Contents
Sidik Isani