This morning I was up at the crack of 4:15. Thank you, Mr. Bladder. I took a peek out the back door and was treated to a very clear sky. Knowing that Ganymede was going around the back of Jupiter, I thought it might be worthwhile to stay up. I keep a 102SLT (OTA on a pipe mount) for a quick grab 'n' go at the door. At only f/6.5, it's not the best on planets, though. I put it outside, and went to get my orange C80 (f/11.3 ).
I would have gotten my dob, but since it was -19C (1F) out, I knew the Sun would be up before it cooled
Brought the 80 out, and since ten minutes had passed, I thought I would take a look through the 102. It should be cooled down, as supposedly 'fracs are way faster at that than dobs. Uh-huh. Tried to focus, no go. Hmmm. Went inside for 10 minutes (coffee), and thought, OK, 4:35, should be good. Been outside for 20 mins. Go back out, a little better, but still no sharp focus. Tried the 80. It was like trying to use my dob after 5 minutes in this cold.
By the time the 102 was good to go, it was ten to five. Nice view, but a little too much CA for me on Jupiter. Over to the 80, and it was still a bit fuzzy. It was 5:10 before it settled into its usual self.
So all that to say, it took the 102mm 25 minutes to cool, and the 80mm 45 minutes.
Is this normal? I've had both out at 10C (50F) and in 5 minutes, they're good to go. I guess 45-50 degrees F might make a difference. I'm wondering if it's the volume or displacement of the air inside the tubes; perhaps that's why the 102, even though larger in diameter, took less time to cool that my long 80mm.
Anyways, just my observations. I've only owned any type of refractor since last summer, so this was new to me. In hindsight, I should've brought out the dob... Still, the view was great through the 80; saw all four moons (including Ganymede, slipping in behind the gas ), and a pinkish dot which I knew was the GRS. So I'm happy. And tired
All the best,