Bringing scope into warm house after icy cold night out

[jah79]

After 4 hours outside I brought the scope in to the warm house. I left all the caps off (including off the EPs). Wiped moisture off scope and mount, put pillowcase over open holes of scope and then replaced all caps the next morning. Is this the correct way of going about things?

I read somewhere that you should replace all caps before going into a warm house and that this is very important to stop condensation in the tube, was a bit worried after reading that coz obviously I did it the other way round. I also peered into the tube after 10mins inside and saw the primary mirror was all fogged up with some different shaded streaks going in one direction.

Thanks

Johann

[acey]

What you did sounds fine - you left the optics uncovered so that condensation could evaporate.

If you cap the optics before entering the house then this will probably prevent condensation on the optics - but not certainly. And if you peek to check then they'll steam up. So there's something to be said for bringing it in uncovered and then leaving it to de-mist.

In practice, certainly with a small scope, I'd expect capped optics to stay condensation free as you come indoors. But a large primary mirror in a cell that allows air to circulate may be apt to steam. I always used to bring in my 8-inch capped, then one morning I opened the tube cover and saw moisture on the mirror from the previous night.

In any case it doesn't do a huge amount of harm. You'll get dewspots (which don't actually affect images), and these can leave tiny amounts of salts on a mirror that will accelerate erosion of the coating, eventually leading to pinholing (i.e. tiny holes in the coating that you can see from the back of the mirror). Once you get lots of those then it's time to recoat - but it takes years.

The streaky appearance is something that intrigues me - my mirror goes like that too. Don't know why.

[Talitha]

Hi Johann, is there a way you could put the OTA into a large plastic bag before bringing it back inside? Airborn particles will stick to condensation like glue and will remain on the optics after the condensation dries. No matter how dust-free you think your home is, there are always particles floating around.

I've been using plastic bags for about 10 years and it works great. The bag prevents the moist indoor air from coming into contact with the OTA. No contact, no condensation.

[George Jones]

I've been using plastic bags for about 10 years and it works great. The bag prevents the moist indoor air from coming into contact with the OTA. No contact, no condensation.

Like a garbage bag for a SCT? How do you seal the bag? With a twist-tie?

[Talitha]

Yes, you could use a twist-tie or just tie the top.. by morning it's safe to open things again. I always cap the OTA and focuser before putting them into the bags, too.

Large trash bags (or lawn and leaf bags) are used for the larger 8" fork mounted SCT and the f/8.3 120 achro. Smaller bags are used for everything else.. 120ST, 80ST, atlases, GEM mount, eyepiece case, sketching supplies, power cords.. the works. If it's being brought back into the house, it gets put into a bag.

My tripod and wedge are the only things that stay outside in a container on the deck.

[Beyond_Vision]

Most houses during the winter time have very little moisture in the air unless you are in the bathroom or kitchen. For example it's 11.6degc and 89% humidity outside and 23degc 47% humidity inside at this moment in time.

When I bring my kit inside and leave it uncapped it is usually sopping wet on the outside already and may have some moisture on the lens if the heaters were not set high enough at the end of the session. It doesn't seem to get any worse bringing it inside. It then dries out nicely after a few hours and then I cap it. Whenever I have capped it whilst there is dampness in the flocking it will still be there when I uncap.

I would just leave it to air then cap it.

[Beulah]

I cap, bring indoors, uncap, then lie the OTA horizontally until all is dry.

[mdstuart]

I bring my OTA in (pretty much always damp on the outside, immediately put all the caps on and I have never had any issue. It certainly does not get any worse inside than it was when I brought it in.

Mark

[jah79]

Thanks for all the tips so far! I'll take the best of each idea and wrap half the OTA in plastic while capping one half of the top outside the house and then uncapping this half and capping the other half inside while storing it at a 45 degree angle in the wardrobe while doubling as a lamp. Perfect!