' FLAT FIELD PARAMETERS
takeFlatsAtSunset = True              ' Set this to True if you wish to take sky flats
                                      ' after sunset
takeFlatsAtSunrise = True             ' Set this to True if you wish to take sky flats
                                      ' before sunrise
nFlatsMax = 6                         ' Maximum number of flat field images which may be
                                      ' taken with each filter
minFlatCount = 10000                  ' Minimum acceptable average pixel count for a 
                                      ' flat field image
maxFlatCount = 50000                  ' Maximum acceptable average pixel count for a 
                                      ' flat field image
saturationCount = 65536               ' Number of counts corresponding to saturation
flatAlt = 75.                         ' Altitude (deg) where flat fields should be taken
flatAz = 0.                           ' Azimuth (deg) where flat fields should be taken
highSunAltFlat = -2.7                 ' Highest allowed sun altitude (deg) while taking flats
lowSunAltFlat = -6.8                  ' Lowest allowed sun altitude (deg) while taking flats
minExpTimeFlat = 5.                   ' Shortest exposure time (sec) which may be used when
                                      ' taking flats
maxExpTimeFlat = 20.                  ' Longest exposure time (sec) which may be used when
                                      ' taking flats

• takeFlatsAtSunset. Set this parameter to True if you wish to take flat fields during evening twilight, otherwise set it to False.

• takeFlatsAtSunrise. Set this parameter to True if you wish to take flat fields during morning twilight, otherwise set it to False.

• nFlatsMax. This parameter specifies the maximum number of individual flat fields to be taken in any given filter. The script will take as many flats as possible (up to a maximum of nFlatsMax flats) within each filter's sun altitude window.

• minFlatCount, maxFlatCount. These two parameters define an acceptable range of average pixel counts for twilight flat fields. Flat fields whose average pixel counts are not between minFlatCount and maxFlatCount are discarded.

  Note: If bias and dark frames have been taken after sunset, all flat fields will be bias- and dark-subtracted using the master bias and master dark frames produced by MU. The average pixel count of a flat field is computed after it is bias- and dark-subtracted.

• saturationCount. This is the pixel value corresponding to saturation. For 16-bit cameras, it is 65536.

• flatAlt. This parameter specifies the altitude (in degrees) of a point in the sky near which flat fields will be taken. This point would normally be located away from the ecliptic (to avoid possible moonlight contamination of the flat fields), at a sufficiently high altitude.

• flatAz. This parameter specifies the azimuth (in degrees, measured from north = 0 deg through east = 90 deg) of a point in the sky near which flat fields will be taken.

• highSunAltFlat, lowSunAltFlat. These two parameters define a range of sun altitudes at which flat fields may be taken. If you use an automated filter wheel, this range should contain all sun altitude windows specified in FilterFile.

• minExpTimeFlat, maxExpTimeFlat. These two parameters define a range of exposure times (in seconds) to be used when taking flat fields.

After taking all flat fields in either the evening or the morning twilight, the MU script combines the flats taken with each filter into master flat fields. Four versions of each master flat field are produced:

In the above table, filterName is the filter name as defined in FilterFile.

Note: If you do not use an automated filter wheel, the filter name will be omitted from the file names of the flat fields.

Click here for details about the directories where flat fields are stored by the MU script.