The Cassegrain autoguider focus should be checked occasionally. The autoguider is focussed manually, which involves the removal of the cover of the A&G box on the autoguider side, unclamping the autoguider assembly, screwing the camera head in and out until the profiles (of a point source) produced by the autoguider software are as narrow as possible, reclamping the device and replacing the cover. All the TV filters, including `clear' are parfocal.