... WFC3 Data Handbook > Chapter 1: The WFC3 Instruments > 1.1 Instrument Overview . 1.1 . ... WFC3 comprises two channels, each optimized for a specific goal: . ... Light coming from the HST Optical Telescope Assembly (OTA) is intercepted by the flat 45 degree WFC3 pick-off mirror (POM) and directed into the instrument. A channel-select mechanism (CSM) inside WFC3 then diverts the light to the IR channel via a fold mirror, or allows the light to enter the UVIS channel uninterrupted. ...