Winter observing, dew question.

[Gimli]

Hey guys, i have a sky-watcher 120mm ed refractor and was wondering what to do with it after taking it home from outside. I was told that after using it outside in the cold, i should bring it home and wrap a garbage bag around the scope so that the dew that formed on the scope dosn't ruin the lenses. Is this the right thing to do? Do i have to be so worried about dew?

Any help would be appreciated. Thanks

p.s. i live in canada, and use it in -10*C.

[Per167]

I have been thinking about more or less the same question. I live in Sweden and have the same low temperature issue as you although this winter has been very mild so far.

The problem is that cold air contains less moisture than warm air. If there is no dew (or frost..) on it when coming in wrapping it up in a bag might make sense as the scope and the air surrounding it in the bag can reach room temperature without being exposed to the (comparably) moist air indoors.

If, however, there is a lot of dew on it I don't think wrapping it up is a good idea. The risk is that the dew on the scope will be more than the air closed in the bag can absorb at room temperature and then it will be like putting the scope in a bag, pouring some water on it and wrapping it up.

I'm sure others will have more practical experience but so far I have never wrapped the scope up if there is visible moisture on it when taking it in. I usually put the lens covers back on my binoculars though before taking them inside if there is no dew on the lens. Might be applicable to a refractor?

[Adrian]

I just put the end caps back on and bring it in - lots of condensation forms on the outside of the scope, but with the caps on the optics should stay fairly clear. Then when the scope warms up the condensation on the outside disappears, no harm done. The morning after I then open the end caps for a bit to let any dampness inside to get out.

If it has been really damp outside then I occasionally leave a little silica gel bag inside the focusser drawtube for a few hours to soak up any moisture inside.

I wouldn't wrap it up in a bag, but I used to drape a towel over it as this is breatheable. I haven't bothered with this for a while though - condensation on the outside is no problem.

[NGC 1502]

When I've finished using my refractor I check for dew on the optics, if there is none then I cap the objective and the diagonal (the scope is stored with the diagonal in place) then place it in the storage case and bring inside to an unheated room. Next morning I check for any dew on the whole scope and leave uncapped to dry out thoroughly.

If you bring an uncapped scope from the outside cold to a warm house, the scope will dew up big time, and take a long time to dry out.

HTH, Ed.

[Craig20264]

Looking at this problem from a slightly different angle.

I have a secure area where I could leave my scope (once purchased) outside, set up.

Is this an option if properly covered up, or would the scope suffer any detrimental effects due to long term exposure to frost etc.

Might be a daft question but i'm still feeling my way around so be gentle.

[NGC 1502]

Looking at this problem from a slightly different angle.

I have a secure area where I could leave my scope (once purchased) outside, set up.

Is this an option if properly covered up, or would the scope suffer any detrimental effects due to long term exposure to frost etc.

Might be a daft question but i'm still feeling my way around so be gentle.

Sounds good to me, similar to keeping a scope in an observatory,

plenty of folk do that. Gives a quick into action set up, and short pack up time at the end of the observing/imaging session.

Regards, Ed.