Quote:
Originally posted by harway7
the GSO plate mirror can have some difficulty handling temps down at around -7C (Canberra).
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I have a GSO Dobsonian and used it down as low as -24 C without any degredation of image quality. Saturn looked very sharp although it was barely 20 degrees up in the sky.
One thing to note however is that the shop that I ordered my scope from made a change on their website immediatly after I purchased mine that this particular scope now comes with a pyrex mirror (previously it was advertised as a BK-7 optical glass). So in the end I honestly don't know if I got a scope with the BK-7 glass or the Pyrex (most likely is the optical glass though).
Observing in cold conditions is a reality here. I have never heard of a mirror's performance bening affected by the temperature, as long at the mirror has been given enough time to reach ambient temperatrue. The only thing I am aware of if that optical glass takes slightly longer then pyrex to cool down.