Some Observations on Scattered Light and Lyman Ghosts Given by Diffraction Gratings

A number of gratings from different ruling engines have been examined in a spectrograph for Lyman ghosts and scattered light. The distributions of light at the exit focus and the distributions of error over the grating surface are complex. The patterns observed give an insight into the cause of the ruling error and, in particular, errors which are repeated several times along a groove length are found to be important.