That veritable master of astrometry, C.G. Tinney, has measured the radial distortion over the TAURUS field of view to high accuracy. The form of the radial profile given below supersedes all previous estimates from Zemax simulations and from  inferior measurements by JBH. This was measured by the displacement of point sources with known positions, i.e. the matrix mask. D.H. Jones confirms this relation in his thesis from the FWHM of stars over the full field. Recall for the MITLL detectors that the pixels are 15um.