With single-pointing photometry the energy distribution of point-like or compact extended sources can be measured in broad-band filters, dust features can be detected with dedicated narrow band filters, and there are some very broad filters dedicated to the detection of weak sources. Fig. 7 gives some typical combinations of filters for different scientific purposes, and the complete set of ISOPHOT bandpasses is displayed in Appendix C.
The large set of apertures in the PHT-P subinstrument offers the study of faint extended emission around point sources, by means of multi-aperture photometry. The largest apertures permit detection of faint and extended emission. This can be done either in staring of chopped mode. For the chopped mode the restrictions in chopper throw described in Sect. 3.1 have to be applied for the largest selected aperture.
