TheSkySearchers

Wondering if there's an average recommended cool down time for small Maks. I took out my new 90 this morning and without waiting I had a look at Jupiter. Mush. The moon wasn't bad though. Collimation seems good and I know seeing plays a part, but it was a bit of a concern.

I realize going from 70 F to 20 F will take longer than 70 F to 60 F.

Thanks.

So what was the temperature differential this moring between the warm OTA and the cold air? Cool down time is ALL contingent on the temperature differential and how much cooling needs to occur.

JT

About 40 degrees difference.

I would set it out about 30 minutes before hand if possible.

Lady Fraktor wrote: ↑Tue Mar 17, 2020 8:41 pm I would set it out about 30 minutes before hand if possible.

That sounds about right, what I remember from when I had a small closed tube Mak.

My sub aperture Mak, the VMC110L, is pretty well good to go in a few minutes.

My MK66 can take 45 minutes. But since it’s a Rutten Mak with 3 secondary collimating screws it announces being good by stars ceasing to be triangles.

Jupiter rides low in Sagittarius now, not a good target to check scope performance.

Thirty minutes sounds all right to me. It is about the same time as my 102mm Mak needs. The 102 Mak may take several minutes more.
Isolating the tubewall on the outside doesn't take the equilibrium time down, as is believed by some. It simply mutes the seeing inside the tube. I take my isolated 102mm Mak out for grab &go on Jupiter as well. Didn't believe it at first. Until I noticed a transit of Callisto, hardly visible in my old 70mm Televue Pronto.

Isolating the tube wall with insulation definitely helps. My 7 inch Mak can take hours to reach equilibrium in winter if brought out from a warm room. If I insulate the tube I can be observing in minutes and when seeing has allowed, 450x magnification was possible soon after setting up. When looking at a defocused star image without insulation, the heat plume from the central baffle is obvious as a rising heat spike, which is not visible when using insulation. Another benefit is it keeps dew at bay. I've had nights where the insulation is saturated, but the corrector lens is dry.

Hmm, question, how does insulating the OTA help with cool down?
Would not the insulation hold the heat in the scope?
What am I missing?

Ylem wrote: ↑Wed Apr 01, 2020 12:21 am Hmm, question, how does insulating the OTA help with cool down?
Would not the insulation hold the heat in the scope?
What am I missing?

It reduces temperature differences. It's differential strain caused by temperature gradients that distort the optics.