The EIS Plate Scale and Raster Step Size#

Nominally an EIS pixel corresponds to 1 arcsec on the Sun, and this is implemented in eis_prep when converting DN to absolute intensities. Below the results from analyzes of EIS data are summarized.

Plate Scale#

Hara (2008) gave an overview of the EIS performance based on early data. He gave a plate scale of 1.002 +/- 0.016 arcsec that was derived from the Mercury transit of 2006 November 8. He noted this was consistent with the expected value of 0.997 arcsec based on the spectrometer design.

Raster Step Size#

Rasters are performed with small rotations of the primary mirror that scan the solar image across the slit. The rotations are discretized to steps of about 1/8 arcsec, with one step corresponding to a motion of about 1/4 arcsec at the slit. For rastering, the instrument is restricted to a minimum of 4 steps per raster position, corresponding to about 1 arcsec at the slit.

Hara (2008) gave a value of 0.1201 +/- 0.0005 for a single step, corresponding to a minimum 0.961 +/- 0.004 step size when performing rasters.

Del Zanna et al. (2011) performed co-alignment of EIS 2" rasters with AIA images and found a plate scale of 1.9", consistent with the Hara (2008) result.