General Considerations

Although the options all provide a PSF to the ASTERIX programs in standard form it is important for the user to familiarise himself with the operation of the individual PSF which he is using, because there are variations in the behaviour of each option. Fortunately there are a number of general considerations which will hasten understanding of a particular PSF ;

• Does the PSF option derived from calibration data or an analytical form?
• Has the PSF been calculated from a generally applicable analytical function or is it instrument dependent?
• Which other PSF options are available?
• Is the PSF onaxis or offaxis?
• Does the PSF simply calculate and apply a single PSF array to a dataset?
• Is the PSF a variable option which attempts to account for the variation of the PSF with energy and variation of the PSF with off-axis angle? (see the Respfile Option below.)
• Is the option intended to be used when working with extended sources?
• Does the option include techniques to improve the speed of processing PSFs?