Mak-casses or SCTs optimized for cooling down?

Last night I had my nice Celestron 9.25 SCT out to observe Saturn. I dutifully put it out in a shaded area more than two hours ahead of time, but once dusk approached the scope had a hard time keeping up with the falling temperatures (maybe 4 or 5 degrees per hour). Every 15 minutes or so while observing I'd do a quick star test, and sure enough the telltale heat plume was still apparent. I was out until about 11:30 and the scope never caught up with the temperature drop.

Once it has cooled the images are really quite good, but it is a perpetual nuisance to wait for it to get thermally stabilized.

I have become more convinced that the best scope for what I like to observe would be an eight to ten inch mak-cass (or SCT) that has been optimized for cooling down quickly. I know the hyper-scarce AP maks have a superb reputation for doing this; are there any other mak-casses or SCTs that come close to cooling as quickly?

The second alternative would be to do some kind of modification to the C9.25 to optimize it for cooling. Does anyone have any experience doing this, or know of any examples?

Thanks and best regards,

Paul

The heat from the mirror gets tranferred into the central baffle tube, and then this heat flows up the tube and out the front of the tube. The resultant plume will not disappear until the mirror is at the same temperature as the inside air. Unfortunately the air inside the SCT tube continues to fall because the aluminum tube (with its black paint) is very efficient at radiating into the clear dark night sky. One thing you might try is to wrap the tube in some insulating material, which will slow down the cooling of the internal air and allow the mirror to stabilize.

Trying to get the warm air out via fans and coolers won't really work. The moment that you remove the cooling device, the mirror will begin warming the air inside the baffle tube and the tube currents will resume.

The cooling problem is at its worst when the sky is pristine clear. That's when maximum radiative cooling takes place. On still nights when the air is damp and the sky is a bit hazy, the scope will perform well without those nasty plumes. That is also the time you will see the most detail on the planets.

Rolando

I agree with Roland as far as the removable coolers are concerned. They don't work well where I live. Once you remove the cooler the plume comes back though the plume is much less than not using one. My temperature drops can be as high as 10 degrees per hour (what I call sunset shock).

In my experiments insulating blankets work for moderate temperature drops in the order of 2 to 4 degrees per hour.

My best solutions have been to use recirculating cooling systems in SCTs. The photo shows a C-11 that was modified with a re-circulating cooling system.

I have made mods to C-8s, C-9.25s, C-11s, and a C-14. I have experimented with passive, active and stirred cooling. I found the stirred cooling to be the best bang for the buck.

Keith

Attached Image:

The six screws on the primary housing and the power plug (located inside the handle) are the only evidence of the stirring cooling system installed on the last C-9.25 I owned.

Keith

Attached Image:

One of these (or one you homebrew) will do the trick:

http://www.lymax.com/

Here is my mod to a C-14 using the "spinning" method.

Attached Image:

Here is a close-up of the fan assembly.

Attached Image:

Here is a rear view of the fan installation.

Attached Image: