PSF Fit Properties

The PSF Fit Properties dialog is used to set advanced properties for radial profile fitting and FWHM calculation. The choice of fitting a Gaussian or Moffat profile to the PWF is also made here. This dialog is opened from the [Advanced] button on the Radial Profile Properties and FWHM Properties dialogs. This is also opened in the FWHM Properties dialog of the Source Extraction module.

Weight fit by Signal to Noise Ratio	Check this box to weight the solution by the Signal to Noise Ratio of the pixel values. Checking the box usually gives a better fit to the point source and unchecking the box usually gives a better fit to the background.
Min iterations for fit convergence	Set the minimum number of iterations for computing the fit. A value of around 200 to 400 usually works well.
Initial estimate for FWHM, in Pixels	Set the initial value for starting the profile fitting. His should usually be within 50 to 100% of the actual Radial Profile, as measured in [pixel] units.
PSF Model	Selects the mathematical model used for fitting the Point Spread Function ("PSF") to the data. The choices are Moffat or Gaussian. For the Moffat PSF, the beta parameter is estimated by the FWHM calculation.
PSF Model	Opens the Moffat Profile Properties dialog for setting the Moffat beta value. The Moffat beta value is the starting point for the calculation as it is a fit parameter. This is an advanced feature.

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