Because the 2K x 2K CCD's in use wih the Hamilton capture virtually the entire spectral format in a single exposure, one might suppose that the placement of the spectra on the chip is permanently fixed. However, because more than one CCD is available for the Hamilton, and because it is sometimes necessary to prevent lines of particular interest falling on bad CCD columns, and because some observers use only a subset of the available orders, it is necessary at the beginning of your setup to place the format on the chip in the way that suits you best.

The format is moved along the CCD in the dispersion direction by tilting the grating. Movement perpendicular to dispersion is accomplished by raising and lowering the dewar on a fine-motion stage. The daytime sky, which, weather permitting, can easily be fed to the spectrograph using part of the CAT optics, provides an excellent map for finding one's position in the format. Thorium-Argon spectra can also be used.

Moves are accomplished with the Hamilton control program's "Grating" and "Height" commands. To move a given number of pixels, one must first convert to the motor-units expected by the program. The conversion constants are 1.15 motor-units per pixel in the dispersion direction ("Grating") and 8.97 motor-units per pixel perpendicular to dispersion ("Height").

Increasing the "grating" motor-units moves a given wavelength to a higher column number (left to right on the image as displayed by the data-taker); increasing the "height" motor-units moves the orders to higher row number (down on the image as displayed by the data-taker).