This directory contains aperture transmission descriptions.

PARAMETERS:

    The following aperture transmission parameters are used.

          title - Title used for labeling of output.
    description - Multiple lines of text used for documentation of output.
     tablescale - Factor by which to multiply the table values.
	   type - Aperture type (circular or rectangular).
       diameter - Circular aperture diameter in mm or pixels.
          width - Rectangular width (dispersion direction) in mm or pixels.
         length - Rectangular length (spatial direction) in mm or pixels.

    The aperture dimensions are optional and provide a default if not
    given as a program parameter.  The dimensions are in mm if the values are
    positive and in projected pixels if negative.  For fibers the diameter
    is normally given in mm and for slits a default of some number of pixels
    may be set.

TABLE:

    The aperture table has two columns for circular apertures and three
    columns for rectangular apertures.  The last column is the fraction of
    light transmitted though percentages may be given if the "tablescale"
    parameter is given as 0.01.  The independent columns are the ratio of
    the aperture size divided by the seeing FWHM, that is, the aperture
    size in units of seeing FWHM.  For rectangular apertures the first
    column is for the width (dispersion direction) and the second is the
    length (spatial direction).  If no table is given then 100%
    transmission at all aperture sizes is assumed.

    Aperture transmission tables can be made for various types of profiles.
    However, the most common one would be for Gaussian seeing profiles.
    The transmission values are then the fraction of the Gaussian profile
    passing through the aperture as a function of aperture size in units
    of profile FWHM.

EXAMPLE

    1. Aperture description for a slit spectrograph.

    # title = "Slit with Gaussian profile"
    # width = -2 (-=pixels +=mm)
    # length = -20 (-=pixels +=mm)

    0.00 0.00 0.000
	...
    0.00 0.63 0.000
    0.10 0.63 0.051
	....
    2.51 0.63 0.541
    3.98 0.63 0.542
    0.00 1.00 0.000
    0.10 1.00 0.071
	....
    2.51 3.98 0.997
    3.98 3.98 1.000

    2. Aperture description for a fiber spectrograph.

    # title = "Hydra red fiber aperture with Gaussian profile"
    # diameter = 0.31 mm

    0.00 0.000
    0.10 0.007
    0.13 0.011
    0.16 0.017
    0.20 0.027
    0.25 0.043
    0.32 0.067
    0.40 0.104
    0.50 0.160
    0.63 0.241
    0.79 0.354
    1.00 0.500
    1.26 0.667
    1.58 0.825
    2.00 0.937
    2.51 0.987
    3.16 0.999
    3.98 1.000

SYNTAX:

    Comment lines begin with '#' and can contain any text and can occur
    anywhere in the file, though normally found at the beginning.

    Parameters are comment lines with the form

	# <parameter> = <value>

    where whitespace is required between each field, <parameter> is a single
    word parameter name, and <value> is a single word value.  A quoted string
    is a single word so if the value contains whitespace it must be quoted.
    Any text following the value is ignored.

    The optional table is a multicolumn list of numeric values.  The list
    must be in increasing order in the independent columns.  Only 1D (two
    columns) and 2D (three columns) tables are currently supported.  2D
    tables must form a regular grid.  The table will be interpolated.
    Extrapolation outside of the table consists of the taking the nearest
    value; thus, a single line defines a constant value for all values of
    the independent variable.  If a "tablescale" parameter is specified
    then the table values are multiplied by this value.
