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Old 13-07-2020, 11:56 PM
Saturnine (Jeff)
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Saturnine is offline
Join Date: Jul 2008
Location: Wollongong
Posts: 1,511
Hi Peter

The moisture on the primary may be promoted by excessive dust on the mirror but 1st, it is an open tube system, so were you using a shroud at all to help keep the dew from reaching the mirror too easily. Also you say it was a damp night, open tubes and cold damp nights aren't a great mix. Having the fans on may have helped for a while but in such an environment it would have fogged up eventually, especially if pointing at high altitudes.
Personally, unless you are using the scope at high magnifications I wouldn't be too fussed about putting it outside to cool to ambient on damp nights. At low and moderate mags. the seeing isn't so critical that the mirror has to be equalised to the ambient temperature unless there is a large differential from the temperature it was brought out from.
In daylight after the mirror has dried off tomorrow, does it look particularly dusty or still have a noticeable ring of discolouration or spot in the middle, a slight staining from the moisture. If not , I wouldn't worry about having to clean the mirror, it will be fine.
No telescope enjoys damp , humid conditions
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