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Telescopes performance decreases as night progresses

Started by Antlerguy, 09/17/2021 01:18PM
Posted 09/17/2021 01:18PM Opening Post
I have been testing all of my scopes. All of them are kept at 74 to 78 degrees.
At night I put them out to cool down. At first images are sharp before cool down. Gradually over 4 to 6 hours it goes very bad.
Here are the tested scopes.
9” apo
11.8” mewlon
C14
Questar 7”
Passive cool down used