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Telescope optics

Finally, the condition of the telescope optics should be stored in a character descriptor named CONDITION in the instrumental ``.tbl'' file. Possible values are 'CLEAN', if the mirrors have been re-coated or cleaned within two weeks of the observing run, and/or a flashlight beam is barely visible on optical surfaces; 'AVERAGE', if a flashlight beam is plainly visible on the optical surface, but the dirt is not very bad; and 'DIRTY', if shining a flashlight beam on the primary produces a sensation of revulsion in a trained observer. Obviously, some experience is required to judge these categories accurately.

Petra Nass