Chapter 2: WFC3 Instrument Description 2.1 Optical Design and Detectors 2.2 Field of View and Geometric Distortions 2.3 Spectral Elements 2.3.1 The Filter Selection Process 2.3.2 Filter and Grism Summaries 2.3.3 Shutter Mechanism 2.4 Detector Read-Out Modes and Dithering