Just finished observing - Condensation Q's

[Petrol]

Just got in after another nights good observing

My problem is that the mirror on my Newt Reflector has some slight condensation on it The outside of the tube is also pretty wet with condensation. At the moment I have a fan heater blowing on it to try to get rid of it. I’m not going mad with the heat though…. It’s a 1KW fan heater about 1M away. Is this the right thing to do to remove the condensation?

Thanks for looking

Pete

[John]

Condensation on the scope / mirrors is not uncommon when you bring it inside from a session, especially as the nights get colder. I don't use any additional heat on mine - just leave the lens caps in place and let it clear at it's own speed. Don't get tempted to wipe the optics.

[pvaz]

It should be ok if you leave it at a safe distance.

Personally I do as John said. I just leave all caps off and the EPs safe on a table and let them dry naturally till the next morning.

In my ep case I have lots of silica gel bags. I have lost optics in the past to fungus so I'm a bit obsessed with keeping the humidity levels of all my optics as low as possible!

[brantuk]

Hi Pete - While it's drying out, leave the scope tube pointg slightly downwards from horizontal so any condensation drips out of the tube rather than down onto the optics. You'll avoid moisture on the mirror in this way and won't get smears if it were to dry out on the mirror.

[peteuplink]

I'm a bit confused here lol.

I've heard that when you bring the scope in from outside you should leave the caps on to trap cold air inside so it'll cool down gradually and not mist up... Or is this wrong?

[pvaz]

When you bring it inside it will warm up.

Probably a confusion with what to do when you take it out to let it cool, before observing.

[James]

I'm a bit confused here lol.

I've heard that when you bring the scope in from outside you should leave the caps on to trap cold air inside so it'll cool down gradually and not mist up... Or is this wrong?

I've heard this too but found out pretty quick that bringing a scope inside will result in dew anyway whether capped or not. Capping it merely kept the dew there longer.

Best bet, if possible is to put the scope in a shed or a garage (i.e. only slightly warmer than outside) then bring it into the house (if that's what the OP is doing) the next day.

James

[peteuplink]

Ahh. I don't have a shed, unfortunately. My yard isn't big enough. What I've been doing is bringing the scope into the house with the lens caps off (I only heard about keeping them on last night and wondered if keeping them off was wrong) and then turning the OTA around on the mount so that it's opening was facing downward and just leaving it alone for an hour or two.

[James]

Sounds like you're doing the right thing then!

James

[brianb]

when you bring the scope in from outside you should leave the caps on to trap cold air inside

Yes. Because even damp cold air becomes dry when it's warmed (as it will be, gently, when brought in). If you bring cold surfaces into warm air they will almost certainly be below the dewpoint & therefore condense. So fit the caps before bringing the scope in.

If the mirror is already misted up, leave the caps off and, as other people have suggested, leave it inside with the tube pointed slightly downwards, leave for a couple of hours until the condensation has cleared naturally before fitting the caps. Or dry the mirrors with a low power heat gun - suitable units are available which run from 12V (jumpstarter unit etc) - mains hair dryers may be too powerful, very fast warming can crack glass.

[NGC 1502]

I do think that brianb is right on this issue, post #10.

If you bring an uncapped scope into a warm house, then the optics

will dew up a great deal more than if you cap the scope prior to bringing it in.

Try not to put the scope into your warmest room. I live in a 3 bedroom house

with just me and the missus, so we dont heat all the bedrooms, I use the smallest

unheated bedroom to store my astro kit. ( I do realise that this is a non option

for many ) I dry off the outside of the tube if its running with moisture, but leave

the caps on until morning, I then do a quick check for dewed optics. Quite often

there is none, even though the outside of the tube had been wet. If there is any

misting up on the mirrors, then I remove the caps until everything is nice and dry.

Regards, Ed.

[WayneR]

We'll all have to save up for DIY observatories!!

[Petrol]

Thank you for your help. I will stick it in the dining room - the coolest room in the house, with the tube pointing downwards and cap off. It also has a laminated floor so I guess there’s less chance of dust contamination.

Once again thanks guys

Pete