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Cooldown Rates: 12.5" ... 2" vs. 1.6"

Started by dwalton, 01/10/2005 02:51PM
Posted 01/10/2005 02:51PM Opening Post
How much more slowly does a 2" thick, 12.5" primary cool down when compared to a 1.6" version? Assume passive cooldown, well-ventilated mirror box, cooldown from, say, 40 degrees to 10 degrees. A lot longer? A little bit? I'm used to waiting maybe 45 minutes to an hour for a 12.5" 1.6" thick mirror to cool to the point where the images start getting good. I know that a rear-mounted fan would accelerate things...

Thanks,
Doug
Posted 01/10/2005 04:37PM #1
Doug,
I have the 12.5" 1.6" and my friend has the 12.5" 2" and his takes 45 minutes longer or even more to cool in an evening. His is also a good bit heavier even though the scopes are identical except for focal length. His mirror box feels heavy compared to mine and he complains about it every time he picks mine up.
Floyd

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 01/10/2005 07:57PM | Edited 01/10/2005 07:58PM #2
Old Fanless Hal,
Don't be so hard on yourself.
I'm sure you have a fan or two on this forum... grin
Have a fantastic evening.
Linton

Posted 01/10/2005 08:11PM #3
Hal,
agreed that if the scope is stored where it stays close to the ambient temperature, cool down is quick or not relevant. But if you go from 60f to 40f quickly, then the mirror will show definate abberations from the thermal boundary layer as it will take quite a while to cool down 20°f.
Floyd

[SIZE="Large"][/SIZE][COLOR="Blue"][/COLOR] Floyd Blue grin
Amateur Imager
Posted 01/11/2005 07:00AM #4
Yeah, if you can store your scope outside, that will eliminate most of the cooldown issue. But if you keep it inside, then it's a real issue. It can also be a problem if you live somewhere where the temperature drops quickly after sunset, since then even storing it outside won't help...

Jarad
Posted 01/11/2005 05:29PM #5
Since I started this thread, I'll now officially close it.

Yes, we've learned much from this discussion. We've heard from lots of folks on their cool-down experiences with various mirrors and scopes under a variety of conditions, and that's what I was looking for. We've also learned that there is a vocal minority out there who disdains any mention of mirror cool-down, along with an associated unique view of astronomy.

Let it be. Thread closed. Thanks to all involved that stayed on-topic.

Doug