Below are results which show the measured FWHM as a function of
distance from the guide star for B, R, and I bands.
Based on the data, once can expect no more that 0.05arcsec degradation up to 2 1/2 arcmin from the guidestar for the B, V, R, and I bands. As one might expect, B-band has the weaker effect and the I-band the stronger. WTTM's performance here is typical, as noted by Claver et. al. (W Tip-Tilt Module Performance) and Tonry et.al. (The Orthogonal Transfer CCD; ASP 6/97), both papers report ~0.05 - 0.06" degradation in FWHM over minimum radial distance of 150".