Stargazing How big of a difference have you noticed with cooling your telescope mirror?

[russ_watters]

Anyone have any experience with cooling a telescope mirror for image quality improvement? I have my C11 disassembled for some other upgrades and before putting it back together am considering adding a cooling fan. Anyone have opinions on how big of a difference it can make?

 

[turbo]

Only in a Newtonian, Russ. Cooling helps speed up steady imaging.

A C11 is petty much sealed up, so if you wanted to add a fan, you'd probably have to make at least two holes in your rear housing. One for fan/intake, and the other for exhaust, and both of the holes should have cleanable/replaceable filters to keep dust and pollen off your optics. You can probably Google for advice on how to accomplish this.

 

[russ_watters]

Yeah, I'm wary of putting holes in my well-sealed SCT. Right now the mirror is perfectly clean. I found an intriguing alternative, using thermoelectric cooleres on the outside and fans to move air around the inside. I'll have to put some thought into whether I want to do this: http://scp3.org/main/index.php?option=com_content&view=article&id=79:installing-peltier-cooling-in-a-c14&catid=76:activecool-cooling&Itemid=71

 

[turbo]

How about making a styrofoam cooler for the OTA and using your engineering skills to bathe the OTA in cool air using dry ice or whatever you can transport to a dark-sky site? If you can get the OTA to 40 deg in preparation for a predicted 40 deg night, that would be a help.

 

[mgb_phys]

You are probably going to do better pre-cooling it to predicted night temperature (or keeping it cool from the night before) rather than trying to actively cool it while observing especialy if you live somewhere with big day/night swings.

 

[turbo]

You are probably going to do better pre-cooling it to predicted night temperature (or keeping it cool from the night before) rather than trying to actively cool it while observing especialy if you live somewhere with big day/night swings.

Uh! Didn't I just say that?

 

[mgb_phys]

Yep - didn't read the last sentence. ;-)

 

[russ_watters]

Well, yeah, what people are doing with the setup I described is just pre-cooling the scope and then turning off the cooler a few minutes before they start imaging so the temperatures can equalize. I suppose if I'm leaving the scope outside for a few hours before using it, I'll get a similar effect.

For Newts, people are leaving the fans on while imaging, but that wouldn't work with a peltier because there would be cold spots.

 

[Chronos]

I leave mine outside most of the time [unheated enclosed porch. I would not put any holes in the tube. The closed tube prevents all sorts of evils from reaching the optics.

 

[turbo]

People with larger Newts can cool optics using some obvious methods. Try to keep the scope out of sunlight to keep the outer parts cool. Try to point the optics pointed at the open sky in order to let the optics cool as night falls. The larger the 'scope, the more likely that you'll have to get inventive to cool it.

 

[chemisttree]

How about a Lymax Cat Cooler, Russ? I've heard good things.

 

[russ_watters]

It's a possibility, but I'm still hoping for the possibility of continuous cooling. I'm not sure how important it is, but I'd rather be set up for it and not need it than have to decide to go back and install it later (taking apart my OTA is something I never want to do again). And I really want to do some testing to find out how big of an issue this is.

So here's what I'm thinking I'll do:
1. Install a heatsink/fan on the inside of the base, with the fan pointing toward the back of the mirror.
2. Install thermocouples on both the heatsink and the back of the mirror to monitor the temperature.
3. Drill and tap a couple of holes to mount an external heatsink and peltier in the future if I want it. If I don't use it, I can just use screws to plug the holes.