You can then check the slit focus/translation. Normally, the slit focus should read zero when WYFFOS is in focus (with no filters in the beam), and +1000 or +2000 for one/two filters in. You can focus WYFFOS using the Hartmann shutters (see Dave King's notes on this **here**), or you can quickly check whether it is in focus by measuring the FWHM of the arc lines in a GLANCE frame. You can use ximtool to display the image and imexam (option k) to measure the FWHM of the lines. The slit translation should not normally need to be adjusted, but can be checked by taking an arc frame and ensuring that all enabled fibres are seen on the CCD.