WFS Gravity dir. If the WFS is being used to track a guide star, it will cause the telescope to move to keep the star centered on its detector in other words, it will remove the deflections tabulated in Table 1, and this correction will propagate to the slit. Table 2 WFS Correction and Net Slit Shifts WFS Correction at Slit Net Shift at Slit Gravity dir. Both of these are well under the 10 m m limit discussed above for light losses or cross-talk. Focus shifts appear to be 1 micron or less, and therefore are neglected.
All values are for the long cameras.
Table 3 Science Detector and Slit Shifts Slit Science Detector Gravity dir. If we consider that the slit is what is re-imaged on the detector, then the values in the first two columns should be used to correct the shifts at the detector. This assumption is certainly reasonable for the dispersion direction, where the long-camera slit is almost always significantly narrower than a stellar image. Along the slit, this assumption is less reasonable, but for Table 4, below, we assume that the slit defines the image in both axes. Table 4 Slit Shifts at Detector and Net Shift Slit Shift at Detector Science Detector Net Shift Gravity dir.