WFC3 Instrument Handbook for Cycle 24 . ... Wide Field Camera 3 Instrument Handbook for Cycle 24 > Appendix B: Geometric Distortion > B.2 UVIS Channel . ... The corner displacements are about 30 pixels, corresponding to 1.3 arcsec. ... The resulting variation of the projected pixel area on the sky requires corrections to photometry of point sources using images that have not been distortion-corrected. ... Figure B.2: Variation of the effective pixel area with position on the UVIS detector. ...