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Subject: "outgassing" haloes
From: Robert Preston
Reply To: mapug@shore.net
Date: Tue Jun 20 09:13:37 1995

One possible scenario is that, IF a halo is caused by deposition of an "outgassing" product from paint or focusser grease or whatever, it may show up only with some paint/grease/whatever lots, or in some scopes shipped and exposed to daytime heat prior to some minimum curing time. It could be a very difficult problem to track. Not everyone leaves their scope outside in the sun during the day, so that the OTA gets very hot and might volatilize stuff that could then re-condense on the corrector plate. But anyway, if the stuff remains volatile (it may or may not, depending on how stable it is) then it might easily be removed simply by warming up the corrector plate (after taking it off the scope) to volatilize the stuff. If it got *on* the plate by condensation (and it's a stable chemical), then it should come *off* the plate by evaporation.

Robert A. Preston Pittsburgh, PA rapr@med.pitt.edu