Dew / fogging / first timer experience

[EagleC]

Hi,

I got my scope for Xmas as hoped. It's a skywatcher heritage 130p flex tube. I also got a celestron omni x2 barlow and a x-cel 7mm Ep. Together with the supplied 10 and 25mm I hope this gives me a good range without going overboard on magnification.

My first targets where Jupiter and the Orion nebula. With the 10mm lens I got a fairly grey image of Jupiter but could just make out the bands but I could not focus the 7mm successfully. I noticed as time went on it was harder to focus and the images became less distinct and detailed. I believe the mirrors and perhaps eyepieces are fogging up. It is making observing very hard and there is no power supply at the end of the garden to run a hair drier from. When I go camping with the scope mains power will definitely not be an option.

I was thinking of investing in a patio heater for home but I don't know if they spew out light too or if the convection currents would mess with the view plus I can't take it camping... Are there light weight all in one dew heater solutions?

Thanks

[Lee M]

If it's a gas fired patio heater it'll be generating lots of water vapour so will probably make matters worse. Plus the other downsides you mention.

Eyepieces you can put in a warm pocket for 10 minutes and that'll keep those sorted. I had 3 in pockets and one in the scope towards the end of the session earlier.

Have a search for dew shield / shroud for the 130P - I'm sure there's some threads on making one up from a sheet of foam. Cheap to do and should help.

[SniffTheGlove]

A patio heater will produce air currents which will make your observing terrible.

If it is dewing up, then invest into a 12v battery and a small car 12v hair dryer to clear the dew.

Invest in a dew shield like Lee says above.

Invest in Dew heaters or make your own, again load of threads on how to do this.

[astronymonkey]

Hi eagle,

unfortunately dew is one of the things we have to deal with and with open tube designs like the flextube its easier for the two mirrors to be affeceted. As others have said a dew shield is easy to make from a camping mat and is basically a tube to slip onnthe front end of the scope and another can be made to go around the middle ofnhe open frame while in use.

one of the other thing tomdo is to keep the scope tube horizontal when you are not usinf it and only point it upward when viewing or looking for something.

The eyepiece in pocket is another good idea but the 12v hairdryer is I greatnsolution and can be used in short blasts of about 5-10 secs and can benran from the car12v socketnif you set up next to the car when camping.

the secondary is usually the one that dews up first so keep an eye on this

cheers

cheers

[EagleC]

Thanks,

When I got back tonight I raided my daughters camping gear for her old ground mat and my wife's craft box for of adhesive Velcro. Took a while to get the shape right but I now haves snug fitting shield. Not sure if I should cut the length down or leave it long like this?

[astronymonkey]

Nice one,

leave it long as this will sheild the secondary from stray side light and reduce the chance of dew being able to settle down the tube.

the reduction in side light can also increase contrast too so as long as its not drooping into the light path and isnt affecting the function of the scope then youre good to go.

cheers

[Moonshane]

thta's a great solution. so much easier than trying to go inside the tube as I have seen before. I agree, keep it long, will be more effective.  waving your hand in front of an eyepiece can help de-fog, as can a large bulb blower.

[EagleC]

I tried again tonight, the sky was moderately clear but damp, the garden squishy and after 15 mins the daughter turned on the kitchen light and floodlit the back garden for half an hour while making some tea so I gave up. In that short time I could not tell if the shield really helped but it didn't hinder. I still could not get the x-cel 7mm into focus.

[DRT]

I use the x-cel 7mm with the same scope as you and it focusses just fine. I have read a few negative reviews about the x-cel EPs with people complaining of occassional quality control issues. I have four EPs from the range and all of them are excellent.

Which other EPs do you have? And are they focussing ok?

[robhatherton]

Hi, if you could focus the 10mm but not the 7mm then light cloud/ haze could be the problem or just unsteady atmosphere - if your skies were anything like ours in Cheshire tonight!

[EagleC]

The 10 and 25 that came with the scope both focused, although even the 10 was not as sharp as I would like. Perhaps I just need to wait for better weather.

[itmo]

it is quite easy to get an idea if something has fogged up if there is a bright star or jupiter visible. just take the eyepiece off, aim at the bright target and look at the defocused image of the target on the secondary mirror. When your eyes hit the mirror, if it has ANY Rubbish on it, your eyes will focus on it. Ice is very easy to see,water a bit harder. If in doubt just use a flashlight. 

For preventing dew, just put a cap on the telescope every time you are not using it. It will shield it from the cold space. Also try pointing it lower , at a house or at anything which is warm. This will atleast slow down the dewing. I use a dew/straylight shield made from camping mat, and that usually suffices even in 98% humidity. One trick I invented (dunno if anyone else has.. ) is to cut a piece of camping mat to match the rear end of your secondary mirror. This will insulate the secondary from the cold space. It seems to help. In my dob one of the problems is that the secondary stalk seems to conduct a lot of the heat away from the secondary so maybe I should insulate it too..