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Hi Fernando
It sounds like what you are seeing is astigmatism which could be one of the mirrors but may well be uneven cooling of the primary.
The 12" mirror is a large chuck of glass and will take a long time to cool maybe a couple of hours with the fan running .
Keep checking the mirror during the night and you may well find it gets better over time.
Failing this if its a truly astigmatic mirror time to see the people who sold it to you .
An F4 mirror wouldn't be my choice for planetary work , maybe a high quality 8" or 10" at F5 ( ie not Chinese ) better a good quality smaller scope than a bad big one.
Hope this helps
Zane
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