Thanks for the replies. Perhaps I haven't been letting my scope cool enough.
Quote:
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Originally Posted by davidpretorius
But don't try and star test without letting you scope cool. Try and let you scope cool for at least 1/2 hr after the temperature outside has stopped dropping otherwise the mirror won't keep up.
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I thought letting it cool for 1-2 hours after dark was plenty. I hadn't really thought about when the temperature has stopped dropping. Perhaps the use of a thermometer to replace experience. Is there a typical time when this occurs. I guess weather varies too much.
Ving, this aperture mask you mention sounds very interesting. I have never heard of them before. Can you tell me more.