On or Off?

[Kirscovitch]

How should I tuck my scope away for the night after a session in cold temps? The last night I had it out it was -5F. As soon as I brought it in the house I noticed frost forming on the outside of the tube. Similar to fog on ones glasses forming when you come inside from the cold but with the extreme temp of the tube it formed frost. 

My gut tells me I should leave the lens cap off and keep it pointed down to let any condensation air dry and trickle down towards the secondary instead of pooling near the primary. 

Also, how bad does extreme cold affect collimation? How bad can alignment change with temp changes?

Thanks in advance! 

[Ben Smith]

I leave mine pointed slightly down with the the dust cover on but the little hole on dust cover open. Seems fine up to now

[brantuk]

"how bad does extreme cold affect collimation? How bad can alignment change with temp changes?"

It can affect collimation and you may have to tweak the collimation a few times per session (depending on how long you're out with the scope and how cold or hot it gets). Dew control helps by keeping optical surfaces consistently just above ambient temperature, but otherwise you just have to check periodically with a star test if you suspect collimation is slipping off.

Same for alignment really - less of an issue but if you have suspicions it's going off or notice a deterioration of the view - then a quick check and a tweak does no harm. Keep in mind that any view deterioration may be due to other circumstances - particularly the seeing.

[m37]

I use a silica gel sachet tucked into the lens cap to soak up moisture. You can buy dessicant caps but this is cheaper!!!

[Naemeth]

Overnight would definitely do it, once it's warmed up above freezing it'll be fine to get inside.

[LouisJB]

I'm not sure, I've been leaving the tube horizonal with all the caps off for 30mins or more once indoors, letting it warm up until there is no visible damp around and it's warmed up a fair bit, then I put the caps on. Sometimes I leave the main tube cap off for as long as possible, all evening even until I'm going to bed, then I finally put it on and orientate the scope back to the normal home position.

Might try the silica idea, guess that's something best obtained from ebay?

[RT65CB-SWL]

...Might try the silica idea, guess that's something best obtained from ebay?

FLO sell replacement sachets! - have a look under Accessories --> Dew Control --> FLO Dual-Fit Desiccant Cap --> Product options: --> 10x Silica Gel Sachets

If you have any empty 35mm film canisters* [removed word] or drill a few holes in the bottom of the canister and insert a few sachets, replace the cap and insert into your 1.25inch eyepiece holder.

I always leave my scopes pointing down on the mount when I get indoors and the objective cap off overnight and replace it in the morning.

* if not you can always ask any photo shop or photo developing booth/shop for some.