[Stonius (Markus)]

So as far as I understand it, dew forms on scopes at night essentially because the telescope tried to reach thermal equilibrium with both the ambient air temperature AND the radiated temperature going out into space (like the inverse of having your scope out in the day and the sun making it hot).

The heat that gets radiated out to space drops the temperature of the scope below that of the surrounding air, and if that point is below the dew point, water condenses out onto the scope. Please correct me if I got that wrong.

So my question is when is the scope at the most thermal equilibrium?

I mean we cool our scopes for as much as an hour to remove tube currents and give us the best views. So is a telescope that is naturally cooled at thermal equilibrium and therefore, has the least tube currents in spite of the fact that the presence of dew would require a thermal gradient between the scope and the local air? Or do we sacrifice a little stability for dew heaters? Or are they simply bringing the scope optics up to parity with the surrounding air (the radiated heat being irrelevant for local thermal currents?).

Cheers
Markus