Another Dew Question

[MalcolmM]

For my refractors, when bringing them back inside, I cap them before bringing them in. This seems to work grand to keep the objective dew free.

I recently got a Mewlon (open ended reflector). When I cap this before bringing it in and look inside it the next morning there is a very fine sheen of dew on the primary.

What is the best thing to do with an open ended reflector? Searches on this forum would suggest:

• leaving in an outhouse all night. Not sure if it should be capped or uncapped?
• bringing in uncapped and pointing down at 45 degrees and leaving to dry naturally
• bringing in uncapped and using a hair dryer at a distance

Is there a best practice or is it horses for courses?

Thanks in advance,

Malcolm

[wookie1965]

When I had my 200p I brought it in and left the cap off and the cap from the focuser until the next morning. 

[TheThing]

That's a very good question.  I've always brought mine in capped, but this is either to an unheated conservatory or; an unheated outhouse.  I've always capped the finder too, but this isn't so much of an issue.  I've not had any dew on the primary of my newt albeit this is a, roughly, similar design but with a much longer tube.  Having now added a Mak and a frac to my collection, I'll need to give these different considerations.

I'll be interested to see what the general consensus of opinion is.  

[Guest]

I just drag mine back into the garage with the cap on and then point it down.  

[bosun21]

I bring my dobsonian indoors uncapped and point it down until the next day when I recap it and turn it back up.

[JeremyS]

Indoors or garage, cap off until next morning

[Adam1234]

I bring it in and leave it facing 45° facing down with the cap off to allow the dew to dry off and escape. 

I do put the cap on before bringing it inside so that no dust falls in, then remove the cap again once I have it pointed down

[MalcolmM]

Looks like there is consensus; indoors, uncapped and pointing downwards at 45 degrees. Thanks everyone!

I'm wondering now should I do the same with the refractors? At least if they are uncapped you know there is no moist air trapped.

Malcolm 

[JeremyS]

24 minutes ago, MalcolmM said:

Looks like there is consensus; indoors, uncapped and pointing downwards at 45 degrees. Thanks everyone!

I'm wondering now should I do the same with the refractors? At least if they are uncapped you know there is no moist air trapped.

Malcolm 

Yes, same with refractors 

[RobertI]

11 hours ago, JeremyS said:

Yes, same with refractors 

Just for clarity, with refractors should we also leave the cap off the eyepiece end so the air inside can dry out? I never really thought about this until I saw those desiccant caps that go in the eyepiece end. 

[JeremyS]

2 hours ago, RobertI said:

Just for clarity, with refractors should we also leave the cap off the eyepiece end so the air inside can dry out? I never really thought about this until I saw those desiccant caps that go in the eyepiece end. 

I don't do that

[Neil H]

Hi I use these on skymax and refractor https://www.firstlightoptics.com/dew-prevention/astro-essentials-dual-fit-desiccant-cap-red.html

And the Newtonian just has cap on and focuser open never had a problem 

[robhatherton]

Refractors: depends if it has dewed up outside already. If not, cap it or it is likely to dew up when you bring it in. If it has already misted over (or frozen up!) you need to leave it uncapped when you bring it in, ideally to an unheated  room where it can demist  slowly. 

Edited October 18, 2022 by robhatherton
Mis spelling

[bosun21]

With my refractors If there was dew I bring it indoors uncapped and point it down. I also remove any eyepieces and rotate the diagonal so that it’s pointing to the floor to stop any dust ingress. Next day I use my blower to remove any dust from the objective and recap, turn the diagonal upright again and fit a desiccant cap.

[neil phillips]

Not sure leaving the cap on is a great idea. I once forgot to uncap my Newtonian. when i checked it had partly dried on the edges, when fully dried after i left the cap off. i noticed it had left a misty film layer over the top. which it hadn't done before. I had recently cleaned the mirrors. So this was noticeable. Still there today. But not going to clean again until real dirty. Now i leave the cap on 10 15 minuets. to acclimatise. then remove. 

[Jules Tohpipi]

I'm still somewhat confused whether any difference in approach is required whether brought into a heated or non-heated room? As some posters are not specifying what type room they're using.

Ideally I'd prefer to bring into an unheated conservatory and leave overnight. However, its large windows often have dew on the inside on the colder mornings. 

So, should I leave capped/uncapped in the conservatory, or best to bring into the heated rooms to avoid morning condensation?