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You don't have dew inside the camera body. If you did it would ice up straight away. You'll get dew on the outside of the glass because it's colder if you point down.
As an exercise take your QHY9 run it for 30min at -20c. Then put it face down on the table and check in another 30min. It's likely you'll get a dew spot on the nosepiece window. I used to shoot my flats by doing that on top of the EL sheet and wondered for a while why I was getting fogging on the glass and halos in my flats.
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