The f/8 collimators have a point-source beam diameter of 12.7 cm (5") and a focal length of 101.7 cm. As with the newtonian flats, two collimators are available; one with silver and the other with aluminum coating. Each should be used with its corresponding flat and the proper focus setting to avoid astigmatism in the image. The optimum collimator positions may be significantly different for the two sets of optics, and KPNO personnel should be consulted for the proper settings. The current values are also listed next to the collimator readout on the spectrograph. The mechanical readout of collimator position on the spectrograph is one-half of the corresponding value at the computer terminal. To manually reset the position, be sure to release both the brake and the locking slide before turning the hand crank. Approach the desired setting from higher numbers. One mechanical readout unit = 50 . Increasing values move the collimator towards the newtonian mirror.