Condensation

[david_r]

I've been getting out for most evenings during the Christmas break, but after an hour or so, everything starts to gain a nice halo! and the finderscope was very poor to the point of being unusable.

The scope is an 8" reflector, and I've been keeping eye pieces etc on the tray on the mount.

I think the build up has mostly been on the eye pieces and finderscope. So I guess for those EPs I'm not using I can store in my pocket, but what about the scope itself, finderscope and the eyepiece installed?

I guess the condensation is building up as the scope is colder than the ambient air temperature, so I only need to warm the main parts up a little to redress the balance. I guess the act of breathing around close proximity of the eyepieces and finderscope makes matters worse.

Anyone know of trace heating cable that you could wrap around the key parts to elevate their temp by a few degrees? Are these commercially available for scopes? Or would something like wrapping it with insulating material like lagging foam be sufficient?

What solutions would you recommend? Do I need to protect the large mirror? What about the secondary mirror as well?

Thanks,

David.

[SteveL]

What you are looking for is a dew controller and some dew strips for the various parts that dew up.

http://firstlightoptics.com/products.php?cat=94

[George]

http://www.firstlightoptics.com/products.php?cat=94

http://www.modernastronomy.com/accessories.html#accDewNot

If you do a search of the forum you will find various homemade solutions.

Also a quick blast with an hairdryer works wonders too, just be careful with electrics outside (use an RCD etc etc)

[Astro_Baby]

A dewshield helps and in any event improves the view by getting rid of stray light.

I keep my EPs in a flight case until they are ready to use and also have a small 12v hair dryer which is plugged into the power tank. A quick blast with the hair dryer is good. Warning - with a big hairdryer dont overheat stuff just a slighlty warm air is all thats needed. Getting stuff too hot will bake crud onto any surfaces s- so just a little warm air - not a jet blast.

Oh and keep the finderscope covers on unless your using the finderscope

[Brinders]

I never have a problem with eyepieces dewing up - like Astro Baby I keep them in a flight case until I need them. My biggest problem is dew on the corrector plate of my 9.25" SCT. I too use a dew shield but on a big piece of glass like that it's next to useless. I therefore also use a Dew-Not heater band and controller from Bern at Modern Astronomy. FLO do a similar system called Astrozap. I find the dew band works fine on even the coldest nights. My little WO Megrez 72 APO is generally fine with just the built in dew shield unless the dew is particularly bad - I'm thinking of investing in an additional dew band for that to hook up to the same dew controller I use on the SCT.

[david_r]

Thanks for the responses. The dew band(s) + controller look like the solution. They're pretty expensive though. As its been cloudy for the last few evenings, in between the single malts I've built my own. Forecast is looking excellent for this evening, so I'll be trying it. If it works I'll post the design of it. (If it doesn't I'll not reply anymore to this thread :oops: )

Cost me the princely sum of around £1.50 max in components, and runs from a 9V PP3 battery.

[Astronut]

I'm amazed at just how effective dewshields are at keeping dew off the secondary - wish I'd got one sooner. I'm still waiting for my Telrad dewshield (out of stock at the moment) - the glass on the Telrad dews up within minutes without it.

[david_r]

Tried my Mk 1 and it worked fine. The basic build is here...

http://stargazerslounge.com/index.php/topic,36694.msg375596.html#msg375596

[lulu57]

I got one of those Kendrick dew shields (admittedly, I've only got 4" of aperture). It works a treat. No condensation during 3 hours of viewing. And I keep my eye pieces covered until they're needed. I've got a proper Celestron case for these, but I found it's actually easier to take out my favourite ones in a Clarins freebie make up case, with bubble wrap for padding.

Clarins - flawless skin coverage and a valuable contribution to astronomy. I should work for their advertising department.