In the midst of a lot of cloud, there opened up a 90 minute window on Tuesday morning of clear skies.
This was the first image of 37 runs, at 09:34UT or 04:34 EST. The Great Red Spot is showing nicely.

A curiousity… the first image was the best. Time to start wondering about the thermal dynamics of the system. The scope is outside in a metal observatory.. at ambient temperature with the inside of the observatory and maybe a little bit warmer than outside.
We open the roof.
I imagine that the OTA starts to cool a little more, maybe 1 or 2 C. It was about -2C outside at the time. The dew heater on the corrector plate was also turned on at the start, to about 50% duty cycle.
So… Is the worsening focus for the next 90 minutes a result of:

Increasingly worse skies?
The OTA continually cooling and not reaching equilibrium with the outside air temp and radiant cooling?
Is there too much unneeded heat coming off the dew heater and is that affecting the optics?

Statistically I find it hard to believe that the first image should be the best. All else being equal, the sky conditions should have given me something good in the 37 runs over 90 minutes, aside from the first.

The OTA would cool down further once the roof was opened… but that should not take more than 10? 20? minutes… it is mostly there already temperature wise.

Can a dew heater running too hot affect optics and focus?

Some interesting questions. To find out the answers I will, next time:
Open the roof and not image for 10 minutes
Take out a remote temperature meter and check the OTA temp every minute from opening until 1st image and then every 10 minutes later.
Not turn on the dew heater until 1/2 way through the session.

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