If specified, the calculated spectrum is convolved with the function found
in the slit_function_file.
slit_function_file file
The file must contain two columns. Column 1 is the wavelength, in nm, and relative to the
center wavelength. Column 2 is the corresponding slit function value. It must
be unity at the maximum. The wavelength steps in the slit function file must
be equidistant. Comments start with #. Empty lines are ignored. Please
note that prior to convolution the spectrum is interpolated to the wavelength
steps of the slit function. For this reason, make sure that the resolution
of the slit function is high enough even if the slit function is e.g. a
simple triangle which could in principle be described with 3 grid points. For an
example see examples/TRI_SLIT.DAT and the make_slitfunction tool.