Most nights I'm using insulation to control the tube currents. On the Colorado plains, many good observing nights are also bone dry. Instead of the temperature falling for a few hours and leveling off, it will keep falling all the way to sunrise. True equilibrium is impossible. I'm just trying to deal with the unending transient as best I can.
Setup time is maybe 15 min before sunset. I start off with my C11's tempest fans running, jacket off. After the first hour or so, I put on the insulation jacket and leave the fans running all night. I'm trying to minimize thermals everywhere, including the corrector plate. The function of the insulation jacket on these nights is to minimize thermals rolling off the tube. Without the reflective jacket, the fans would be have to heat up the metal tube as the tube otherwise would radiatively cool well below the ground-level air temperature. Adding the jacket means that the little tempest fans can follow the air's 3-4 F/hr unrelenting cooldown rate as the night progresses.
Does it work in this mode? To be perfectly honest, I'm not entirely sure. Certainly the telltale mirror plume in a defocused star isn't there (and was everpresent before I adopted this strategy). Similarly, the radial waving threads/spikes disappear and don't come back. But living just east of the Rockies means that seeing conditions are generally poor. Looking at the moon is surreal; as if the moon was at the bottom of a swimming pool. Planetary viewing is an act of patience, as the image phases back and forth through both sides of focus. In the naked eye, the planets can twinkle just as much as the stars do. I've never seen the Airy disc's first ring in my telescope without an artificial star.
Although much less common, dewing or frosting can be a threat even up here on the high plains. On humid nights (like last Saturday) I turn the fans off after the first 45 min or so when I put on the insulation jacket. In this case, I'm trading off a little more thermals around my corrector plate to get some more dewing resistance, but I still want to get somewhat closer to ground-level temperature. When I started packing things up last weekend the status was:
- Telescope OTA plastic crate: dewy
- Observing notebook: wet
- Car roof: wet
- Eyepiece pelican case: damp
- Car windshield: fogged
- Telescope insulation jacket: dry
- Telescope corrector plate: dry
- Astrophoto refractor guy on the next pad: Grumbling about dew-ruined subs
- Open-truss dob guy on the next pad over the other direction ... still happily observing with his boundary-layer fans
I don't even own a dew heater. Just a dew shield and single-layer reflectix insulation jacket. I'd've stayed out longer, if it wasn't for the fact that my observing buddy was passed out in the car secure in the promise that daddy was gonna take her home Real Soon Now
Elwain's strategy is different. He's starting the night off with a robust insulation jacket and zero fans for grab-n-go use. He's accepting a little more corrector plate thermals in exchange for low (negligible?) mirror and tube thermals right away. He's also aiming for maximum dewing resistance in a humid climate. I don't do much grab-n-go in the Denver suburbs, but I think the basic strategy is totally legit and I'll be doing the same thing on my smaller scopes in the future.