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4.4 Dewar Rotation

With such a large spectral coverage, it is evident that the dispersion direction is not precisely along rows when the slit is projected along columns. This will vary from grating to grating depending on how well they are aligned in their cells. Distortion is also visible as the ends of the chip are considerably off-axis. In particular, the comparison lines and night sky lines are really curved, especially when using high angle gratings. The chip rotation will normally be adjusted on the first night.
Wed Aug 2 13:05:25 MST 1995