Fighting dew without power?

[newman]

Hi all,

I have a 120mm f8.3 refractor, equipped with a dev cap. On a recent observing session the dev cap proved inadequate to the task, and the lens was totally wet after about 2 hours (which is probably good, considering I have no heating elements).

I was considering getting dew heaters that wrap around the dew cap / eyepiece and a 12V battery to power them. But then I started thinking about possible simpler alternatives that don't require power in the field (I have an undriven mount and for now, that's how I like it. So apart from the heaters I have no need for power sources in the field). I then saw someone keeping the soil in plant pots a few degrees warmer by wrapping the pots in styrofoam pads. Apparently it works for that.. so that got me thinking. I could get a few styrofoam panels, cut them in the appropriate shape, aperture hole included, then glue them together to get the height I need. Then I just pop that over the dew cap whenever it's cold and humid outside.

What I'm wondering about is whether or not this approach might give me some extra viewing time in the field without having to resort to complicated solutions with powered heaters and batteries that need to be lugged around and maintained. Opinions? Could this actually work? I realize it won't be as good as heaters but if it gives me an extra hour or two, that's pretty much all I need..

[Bizibilder]

Many folk make dew shields out of camping mats (sometimes called Yoga mats) from shops like Tesco. Just make a tube that fits over the dew shield and is about twice as long as the dew shield - it makes a huge difference!

Another hint is not to observe too near the zenith (overhead) as the radiated heat from the optics can escape easily upwards, cooling the optics, and allowing dew to form more quickly.

If you don't have power but are at home (ie near a power source) then you can use one of those "neck warmers" that older folk use for their aches and pains - the things filled with seeds or similar that you heat in the microwave oven. Warm it up and wrap the scope in it for a few minutes!

[newman]

Thanks for the advice, the camping mat idea sounds good. One factor I (nearly) forgot about is the dewing of the eyepiece - I don't fancy cleaning my Ethos of dew-induced mess too often. So I think I'll just bite the bullet, get a 12V rechargeable battery and hook up two heaters on it.

[NGC 1502]

Or how about some single use hand warmers, elastic banded to the lens cell ?

They are available very cheaply from my local market, and 'Pound Shop'.

That plus a camping foam dewshield could be a lo-tech solution.

Regards, Ed.

[sbooder]

Also you could try flocking the inside of the foam matting for that extra insulation and it makes the inside of the matting mat black, as they have a little bit of a sheen to them.

As for EPs, I tend to change them when they begin to cloud, this sometimes means changing the object I am viewing because of which EP I put in its place, but hey, it makes for a more interesting night.

[newman]

Yea, the Ethos has an unfortunate side effect comparable to the One Ring (to rule them all); the more you keep it in the diagonal, the harder it is to take it off. My preciousss..

Thanks for the advice, everyone! I'll chime in once I've cobbled a solution together and had a chance to test it out.