How to cool your telescope

[bloodhound31]

Well, I raided the tip for some computer fans and coolers....I have been a busy boy tonight.

I was a bit nervous about pulling the scope to bits to do this, but it is well and truly out of warranty now and I am fairly confident I know what I am doing....

I will be writing a FULL tutorial and have LOTS of photos, so stay tuned folks!

Baz.

http://i26.tinypic.com/21do95d.jpg

[a-l-e-x]

How long should it take to cool down an sct without a cooler? Im going to assume an average room temp of 75F and an outside temp of 50F. Would 30min be acceptable? How about 1 hr?

[LotusExcelle]

I have a box of above-normal quality fans (some squirrel-cage style) that would likely fit this application perfectly. I don't have scope though so they are free plus shipping to whoever want them.

[spaceboy0]

I just take the lid off my Newtonian; I didn't think it was any more complex than that

[aurora]

How long should it take to cool down an sct without a cooler? Im going to assume an average room temp of 75F and an outside temp of 50F. Would 30min be acceptable? How about 1 hr?

Depends on how fussy you are.

I often find that with no fan, it never cools down enough because the mirror is always just a little behind the air temp. As the evening goes on, the air temperature continues to drop.

[redshifter]

I bought the Orion fan for my Orion XT 10, seems to have cut the cool down time by half. http://www.telescope.com/control/product/~category_id=mount_accessories/~pcategory=accessories/~product_id=07816

[spaceboy0]

yeah but having the fan on will screw up the seeing, yes?

[aurora]

yeah but having the fan on will screw up the seeing, yes?

You can turn the fan on and off, as needed.

I find that with a small fan on the back of the mirror, it actually hurts the seeing very little so sometimes I leave it on when viewing.

[spaceboy0]

I have a shower cap over the end of my 8 inch Newtonian where the main mirror is to keep dust out.

If I had the shower cap off, would the Newtonian cool down better and offer better seeing?

[aurora]

Yes, the telescope will cool down better with the shower cap off.

[a-l-e-x]

Im thinking of getting a large refractor (6"). How long is the cooldown time for this? About 30min?

[redshifter]

Im thinking of getting a large refractor (6"). How long is the cooldown time for this? About 30min?

Depends on how warm the storage facility is, how cool your observing location is (IOW the difference between what temp your mirror/lens is stored vs. the temp to which it has to cool down to), and how thick your mirror/lens is. 30 min should be sufficient in most cases. It might be longer if you're storing it at room temperature and observing in below freezing temps.

[a-l-e-x]

Yes, Im going from room temp (75 degrees) to about 60 degrees (outside). In the fall, it'll be about 45-50 degrees and in the winter, under 32F. So, is it reasonable to assume it should be around 30min for now thru the fall and perhaps an hour in the wintertime?

[redshifter]

That's probably a sufficient cool down time. Do you have a dew shield and/or heater for the lens? Otherwise dew could be a problem, esp. in winter depending on how humid your climate is.

[aurora]

During cooldown of a refractor or SCT, or when you are not looking through it, point it at the ground.

If you don't have a dew heater, pointing it at the ground will prevent or delay formation of dew on the front lens. This is because dew forms when heat escapes to space and the object becomes cooler than the air.

[a-l-e-x]

Thanks for the tips guys. I do have a dew shield, but not a dew heater. I might need to get one as humidity is always over 60% here at night in the summer. Even indoors! I hope I dont have to worry about mildew/mold forming on the inside of the OTA when I store my scope indoors at night!

[Moonhawk]

I had an idea for SCT cooling - which involved a threading a fan onto the back of the OTA (and therefore no OTA modifications required)

Doing a quick search on google turns out i'm not the first to have the idea :whistle:

http://www.lymax.com/sct/

http://www.lymax.com/sct/in2inchvisback3a.jpg

[bloodhound31]

When you live in a place like Canberra, where the temperature plummets so quickly to minus, you need your optics to keep up with ambient.

SCT's are a sealed unit because of the corrector plate, unlike a Newtonian, which is open to the outside air.

Now, I have brought my mirror down to ambient in 35 minutes with this mod. Before the mod, it took least a couple of hours, but if the temp outside drops too quickly, you never catch up.

eg. a couple of hours ago it was 5 degrees C in the observatory, now it is minus 2.2 degrees C.

I turn the fans on prior to imaging, then turn them off when ready to image.

[bloodhound31]

All done!!!

With inspiration and guidance from Paul and Anthony (They developed this method) from Southern Celestial Pole, I have completed an active cooling modification and tutorial on my C11 SCT, using Peltier coolers.

http://www.asignobservatory.com/CoolingModification.aspx

My thanks to both of them for their encouragement and backing to share this around.

Cheers,

Baz.