Similarly to the shift in the Fabry mirror image discussed in the preceding section, small shifts in source position (a few pixels at 1.5 arcsec pfov) can occur when changing filters. Similar, larger shifts (up to 8 pixels in the 1.5 arcsec pfov) occur when using the polarisers or CVF. In general, the shifts are negligible/undetectable using larger than 1.5" pixel fields of view, but turning the lens wheel can cause shifts of up to 1.5 pixels in the 6 arcsec pfov. The larger shifts may in part be due to systematic effects which could later be reduced, but users are cautioned to consider whether such shifts in source position could substantially affect their observations. Note that the coordinates in the FITS header of the data cannot reflect these shifts and hence can be in error by a comparable amount.