urn:nasa:pds:context:instrument:keck.10m_keck2.echelle 1.3 1.25.0.0 Product_Context 2026-07-07 1.3 Removed duplicate Internal_Reference entries from Reference_List. 2025-12-24 1.2 Updated schema version. Adding missing "telescope" references. 2025-01-02 1.1 Updated schema version. Update instrument type/subtype to use valid CTLI LDD. 2020-02-18 1.0 Initial export from OLAF urn:nasa:pds:context:telescope:keck.10m_keck2 instrument_to_telescope Keck Echelle Spectrograph and Imager Spectrometer Imager The Echelle Spectrograph and Imager (ESI) at Keck Observatory operates in three modes: echelle, low-resolution, and direct imaging. In echelle mode, it captures ten orders with a wavelength range of 3900 to 10900 Angstroms, with varying dispersion from ~0.15 to 0.30 Angstroms/pixel depending on the order. The slit widths available range from 0.3 to 6.0 arcseconds, and the system has a velocity dispersion of 11.5 km/s/pixel. In low-resolution mode, it uses prisms for linear dispersion, ranging from 0.8 to 11 Angstroms/pixel, with multi-slit capability and a longer slit length of about 8 arcminutes. The direct imaging mode, with prisms removed, provides an 8 x 2 arcminute field with good imaging quality, although the original BVRI filters were undersized. The system was capable of achieving image quality of 0.34" FWHM during commissioning.