Condensation...dew....any solutions?

[pianorealm]

Hi.

I'm new to astronomy. I have a Skywatcher 130p. A few nights ago a clear night was forecast. So I set up my scope in the garden, before it went dark for it to 'cool down'.

I then took Bobbie {woof} for a decent walk.

I returned a couple of hours later full of anticipation and looking forwards to some good views of Jupiter and later Saturn. {that's my extent of knowledge of the night sky at the mo}

But............I first thought something was wrong with the telescope.......couldn't focus at all....very blurred image.

Then I realised it was dew/condensation on the optics.

Surely this can't be an issue all the time? I mean.....is it due to a sudden drop in temperature...I didn't notice one?

Or is it an occupational hazard so to speak?

Regards, Howard

[Wildwood]

Hi. Yes it is I'm afraid. Make yourself a dew shield out of a cheap camping mat. I also use a dew strip as well.

[Steep]

While letting it cool down, don't leave the scope open at the top or if you have to then make sure the scope is horizontal so dew can't fall into it. If the dew is getting in while you are observing you need to make yourself a dew shield. For that camping mat is very good since it's light and flexible. If you have a Lidl nearby they are selling camping mats just now for £5.99 http://www.lidl.co.uk/cps/rde/SID-CA666419-CF561610/www_lidl_uk/hs.xsl/our-offers-2491.htm?action=showDetail&id=1667&ar=11

What you do is make a tube extension by wrapping some mat round the top of your scope. This works really well unless you're pointing the scope near vertical.

[jason.p]

To avoid condensation on the eyepieces you can keep them in your pockets to keep them a few degrees above outside temp. I keep mine in bubble wrap bags to keep "pocket dust" off of them. You can devise a system so that you know which ep is in which pocket so you can find them easier in the dark. If that fails, then a hair drier set on medium or cool should do the trick. This can also be useful for the finder, Telrad etc.

[swamp thing]

Dew shields can realy help. I make mine from floor protection sheets. This is corrugated plastic sheeting. Tuff, rigid, easy to cut, waterproof and Velcro sticks to it.

[Mattscar]

Does anyone have a picture of something like this? I too sometimes suffer from the same problem and work better from pictures. I happen to have a spare camping mat and want something to do while the weather stays rubbish.

[Mattscar]

I feel I should clarify - I don't mean because I don't know what one looks like, as a quick look on FLO gives the idea, but if I made one myself I'd be forever wondering if it should be literally extending the length of the tube by having half a foot or so of it over the edge as it were or have it flush with the tube for fear of doing something fruity to the focal length.

[jonathan]

I just buy AstroZap dewshields, pre-made and pre-cut to fit over scopes of most sizes, complete with Velcro and soft grip band.

[bbottle]

I noticed that you said that you have a Skywatcher Explorer 130P. This is a short tube Newtonian reflector. Generally these do not tend to suffer too much from dew directly on the mirror, although I agree with the advice that you should either cover the tube during cooling or point it level or slightly downwards to stop dew dropping down the tube. An extra length of tube (which is effectively what a dew shield is) may help slightly, although these are more effective on refractors and Cassegrain scopes. Putting your eyepieces in pockets to keep them warm is quite effective as well (do not leave these out uncovered). You might want to think about a heating band around the eyepiece tube eventually.

[jonathan]

It should also be noted that some nights are just really bad for dew, particularly in the cold damp winters. If you touch the metal casing of the scope and feel that it is wet, it's a bad night for dew, and that's when having a dew shield and possibly heater tapes can hold off the dew for a while (but probably not all night). By contrast, I had my large SCT out the other night (well known for their dew attracting qualities) and there wasn't a drop on it, I probably could have got away with just a dew shield or nothing at all, but those dew-free nights seem rare in the UK.

It's a good idea to keep your eyepiece case (if you have one) closed except to take out an eyepiece or put one back.

[Mattscar]

I do keep my EP's in the inside pocket of my coat as its the right temperature and there is no pocket fluff ever in those pockets.

I've had the outside of the tube dew up on me a couple of times, but its not every time by any means so I may just stick with what I'm doing and see how it works out.

If anyone does ever use a dew shield on a 130p Id like to know the results though

[Stargazer_00]

i dont put my scopes out too long before dark as roosting birds have a habit of dumping before they settle up. last thing you need it bird cack on your scope, or worse - in it. I got a warning shot once when I came out and found bird poop on one of the legs of the scope. near miss. My scopes live in a shed now so I just crack the shed door open for 30 minutes before I get the scopes out

[Mattscar]

Thankfully for me there is a small porch out the back, otherwise I would suffer from the same problem.

One got my bag while walking to work the other day, atleast I could tell he was having a very berry diet.

[valleyman]

Here is one I made for my C11. You need to make one which extends for about 2xdiameter of your tube.

It is most likely the secondry mirror that is dewing up, what ever you do dont touch it with your fingers to clean it.

Cost of the dew shield was about £8. Camping Mat and Velcro from Halfords.

[Bart]

I made a dew shield for my 10" but found one for the 16" was way too big and cumbersome it looked like a SCUD missile launcher. Instead, I use a hairdryer once or maybe twice during a long session. Hoping the neighbours or my wife don't hear it or I'll be in trouble. If I'm out, its usually still outside and the noise travels. At 1am, the hair dryer sounds like a jackhammer! or maybe its just me waiting for someone to shout out a window!

For 12" definitely 10" down a shield is grand.

Barry

[pianorealm]

Thanks to everyone for their help and advice. Reading through the replies....I can't believe how dim I've actually been. Yes...I did leave the scope with the cover off.....I did leave it pointed upwards, I did leave the eyepiece in it. Well at least now I know.

I like the idea of a dew shield....will pop along to Lidl ASAP and get the mat to make one.

Regards, Howard

[LukeSkywatcher]

Hi. Yes it is I'm afraid. Make yourself a dew shield out of a cheap camping mat. I also use a dew strip as well.

On a 130mm scope, a simple dew shield made from a camping mat will help keep the optics from fogging/dewing up. No need to invest in a heated dew strap.

As said above............the dew shield should extend outwards from your scope about 2-2.5 the size of the diameter of the scope..............so on a 130mm scope............about 260mm (10")