The y axis corresponds to points along the slit, while the z axis corresponds to points along the spectrum. The WFS detector is rotated about the y axis by 50 degrees, so it is not close to either the xy or zy planes. The coordinate system described above and its relation to up and down refer to the standard orientation we have been using for the bench layout. The shift of the axial ray relative to the WFS detector and to the spectrograph slit are given below. Only shifts in the plane of the detector and slit are given, as focus shifts at both locations were well under a micron.
All shifts are in microns.
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.