ESI Slit Tilt Comparison

Six 4x4 inch reflective masks were made by the Lick shops, each tilted at a different angle: 8.9°, 9.0°, 9.1°, ..., 9.4°. Only two mask holders were available, each with two available positions, so only the 8.9°, 9.1°, 9.2°, and 9.4° masks were tested. The echelle slit center was estimated to be (x,y) = (465,943). In the diagram below this is represented by the sharp dip in the crosscuts, caused on these masks by a crosshair pattern cut into the center at the slit position.

The figure below shows vertical crosscuts through the guider images. The abscissa represents the guider Y direction; hence 943 on this access is the approximate slit center. Note that the 9.4° slit peaks just left of the slit center, at 935. The 9.2° slit peaks near 885, the 9.1° slit at 862, and the 8.9° slit at 795. Extrapolating slightly above the 9.4° result gives a recommended tilt value of 9.45° for the optimum illumination at slit center.

ESI Master
23 October 2000