1. StarFinder seems to do a great job at finding point sources in crowded fields. It includes a routine for generating the Airy pattern. For a 51 x 51 array, with the peak at [25, 25], and an FWHM of 8.0 pixels, this is the command:

psf = airy_pattern(51, 51, 25, 25, 2./8.0)
isurface, psf

The output looks something like this:

2. The IDL Astronomy User's Library contains a routine, psf_gaussian, that produces a Gaussian PSF. To produce the same as above, the command would be:

psf = psf_gaussian(npix=51, fwhm=8.0, /double)
isurface, psf

... which produces something like this:

• IDL Workbench rocks! (This is because it is basically Eclipse, which is a proper development environment, unlike that hideous old IDLDE.)
• Another reason for using IDL Workbench (for me at least, and for now) is that IDL help doesn't seem to work if Java 6 is the default (as it is on my Mac), but the help does work if launched through the IDL Workbench.

To transition to IDL Workbench:

1. Import your code as described on David Fanning's page - fret not, it's easy and harmless
2. Preferences -> IDL -> Startup file, if you have one, and
3. Preferences -> IDL -> Paths -> Insert... for me it was just my idl folder, including all sub-folders, to mimic my $IDL_PATH environment variable.