Changes

* Acquire a ~11th mag star (e.g. one of the spectrophotometric standards) with the guide mirror in the beam.* Position the star on the appropriate red box on the acquisition image.* On the instrument schematic, set the guide mirror to Science (so that light reaches the slit).* Also 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 bars at the bottom of the image (both most of the way to the left) to set the brightness and contrast.* Use the hand-paddle to position the star near the centre of the slit (in both X and Y).* Adjust the telescope focus with the hand-paddle 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 with the hand-paddle if necessary.* Astigmatism in the system extends the star image diagonally and the orientation indicates whether the focus is too high or 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 night may be closer to 2250 units