If you string together consecutive raster images into a movie, you will find that the field of view moves around in time. For rasters of duration 30mins or more, this will translate into an apparent distortion (flexing) of the image. Some examples are available at:
the pointing wobble seems to be about 3-5 arcsecs in X and Y.
Shimizu-san (private communication) has stated that XRT and SOT are co-aligned to within 0.5 arcsec. For EIS it is only 5 arcsec.
It seems that there are some distortions occurring within EIS (structure, mirror, grating?) over time that are causing this wobble in the EIS images.
Note that this means sit-and-stare observations with EIS are not recommended!
Peter Young