8.5 CMAP Files

• CMAPs are constructed using the reference celestial coordinates from the IRPH files with no correction for the IIPH pointing jitter which, though small, causes image blur of about 1 $^{\prime \prime }$.
• As indicated in Chapter 4, straylight generated ghosts can lead to spurious extended features in images. Ghosts seem mainly to affect CVF data with pixels larger than 1.5 $^{\prime \prime }$ (Biviano et al. 1998b, [6]; Okumura et al. 1998, [45]).
• Lens and filter-wheel jitter can lead to imperfect flat-fielding at the edges of CMAPs, where errors up to a factor of 5 may occur.
• In SW observations of a strong source the dark current may be overestimated, which leads to an apparently negative background.