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WFC3 Data Handbook V. 4.0 |
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WFC3 occupies WFPC2's spot in HST's radial scientific-instrument bay, where it obtains on-axis direct images. 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. Because of this design, only a single channel, either UVIS or IR, can be used at any one time. Optical elements in each channel (anamorphic aspherical correctors) correct separately for the ~1/2 wave spherical aberration of the HST primary mirror. Both channels also have internal flat-field illumination sources. Figure 1.1 shows a schematic diagram of the instrument's optical and mechanical layout. The main characteristics of each channel are summarized in the following sections. For a technical description of the instrument's properties, performance, operations, and calibration, please refer to the WFC3 Instrument Handbook.Figure 1.1: Schematic optical layout of the WFC3 instrument