We have used the C100 camera of the ISOPHOT instrument to obtain ~ 80 maps around both hot and cool stars, using the AOTs PHT 22 and PHT 32. Extracting the faint fluxes from the strong background requires considerable care in the data reduction. We have noticed certain peculiarities in the behaviour of the C100 detector, of which we present some examples. We discuss different possible explanations and suggest a number of solutions.