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8se cool down time and dew formation

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#1 omcbman

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Posted 21 December 2013 - 07:13 AM

:question:Hi everyone just wondering how long i should let my 8se cool down in colder temps before use? also ive noticed alot of dew forming on the primary once back into a heated area after a short period of being inside it disapears is this normal and will the dew hurt my optics?

#2 Tel

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Posted 21 December 2013 - 07:39 AM

HI Omchman,

It depends on the "starting" temperature.

If you are moving your 'scope from a warm house to a cold outdoor environment, the general advice you might be given is ca. two hours for the 'scope's temperature to equilibrate with that of outdoors.

However, the effects of temperature imbalance, i.e. thermal currents within your OTA, will only really become noticeable if you use high magnification. (These effects, of course, will diminish the longer the 'scope is allowed to cool outside).

I would therefore say, place the 'scope outdoors: give it fifteen minutes and then use a long-ish focal length EP until, by experimentation, you are able to use shorter ones. Basically, there's no hard and fast rule !

As to bringing the 'scope back indoors after an observing session, just leave the covers off the tube until the temperature once again equilibrates with that of your room. The dew should by then, have disappeared and the dust caps can thus be replaced.

Hoping this helps,
Best regards,
Tel

BTW. You might turn the OTA upside down to allow the warming air and moisture within the tube to escape via the visual back but I don't think it critical. Certainly I've never had a problem with dew removal after observing sessions.

#3 omcbman

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Posted 21 December 2013 - 08:42 AM

Thanks Tel as usaual you always come through.

#4 omcbman

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Posted 21 December 2013 - 08:44 AM

usual

#5 coutleef

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Posted 21 December 2013 - 10:06 AM

When i allow my scope to cool down i place it outside in a plastic box for 2hours in winter. I bring it in inside the box, so no dew or condensation






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