12.5 Tabular Data

12.5.1 TPG_TIME Values

The following table gives the legal TPG expose times (TPG_TIME) in seconds, needed to calculate legal exposure times in ACCUM and ACQ Modes. These values are approximated for simplicity, so that exposure times derived from them may be reduced by up to 1 msec.

12.5.2 NICMOS Apertures

Each camera has two apertures defined near the center of the FOV. Only exposures using the corresponding configuration (NIC1, NIC2, NIC3) may use a given camera's apertures. The CAMERA-FOCUS optional parameter may be used to select a compromise focus position not optimized for either NIC1 or NIC2, but intended to work well with both.

One of the two FOV-center apertures (NIC1, NIC2, NIC3) is an optimal location near the center of the FOV considering detector efficiency and pixel quality, which will be updated by the STScI as the detectors change on orbit. One aperture in each camera (NIC1-FIX, NIC2-FIX, NIC3-FIX) corresponds to a fixed pixel at or near the center of the detector array, which will not change on orbit.

The aperture NIC2-CORON is the location of the coronagraphic spot in the NIC2 camera. It will be used by science exposures which have been preceded by a target acquisition exposure using the NIC2-ACQ aperture or by a real-time acquisition image obtained using the NIC2-CORON aperture. The acquisition aperture will be slightly offset from the coronagraphic aperture, but within the acquisition detector subarray.

12.5.3 NICMOS Spectral Elements

The following Spectral Elements, including filters, polarizers, and grisms, are available for the three NICMOS cameras. Only exposures using the corresponding configuration (NIC1, NIC2, NIC3) may use a given camera's spectral elements. The CAMERA-FOCUS optional parameter may be used to select a compromise focus position not optimized for either NIC1 or NIC2, but designed to work well for both. See the NICMOS Instrument Handbook for details.