===Focusing the telescope===
* Acquire a ~11th mag star (e.g. one of the spectrophotometric standards) with the guide fold mirror in the beamand the guide camera focus at ~29000.* Position the star on the appropriate red box on the acquisition image.* On the instrument schematicTCS, set move the guide fold mirror to Science out of the beam (so that light reaches the slit).* Also On SpUpNIC, insert the rear-of-slit mirror into the beam to direct the light to the Lodestar (rear-of-slit) camera.* View the stand-alone rear-of-slit software window . * Click on the "continuous" button for an ongoing series of 2 second exposures.* Open the slit wide, to about 4".* Adjust the slider bar to the right of the image to adjust the scaling, or hold down the mouse button while mousing over the image, as in ds9 .* Using GUIDE speed, use the RA & Dec arrow buttons on the bottom-right of the TCS GUI (or the hand paddle if in the dome) to position the star near the centre of the slit (in both X and Y).* Adjust the telescope focus on the TCS (or the hand paddle if in the dome) in steps of 3-5 units and assess how the star image changes.* The star will move around due to the translation of the secondary mirror, so adjust it back into view if necessary.
* Astigmatism in the system extends the star image diagonally and the orientation indicates whether the focus value is too high or too low:
Star extended from upper-left to lower-right: focus value is too high
Star extended from lower-left to upper-right: focus value is too low
* Best focus is where the star is as round and sharp as possible.* Optimum focus varies with temperature, typical summer values are ~2200 while cold winter nights may be closer to 2270 units.
===Focusing the acquisition camera===