Eyepeice Warmer

[Carbon Brush]

The recent very damp weather seems to have brought up a few queries about dealing with dew.

The heater tape techniques are well known for the scope and can be extended to finders and eyepiece barrels. But for eyepieces not actually on the scope, I haven't seen anything better than putting them in your pocket.

So last winter I put together this kit. It is a GRP thick walled box. Strong enough to stand on or kick, and it insulates well. The top hinges open. Inside the lid is a fan and a couple of power resistors, all screwed to the plate. In use, the resistors heat the aluminium plate. The fan transfers the heat to the air in box, and keeps the air stirred, encouraging evaporation.

In the base is some foam about 6mm thick. There is no attempt to support or wrap any parts as this would discourage air circulation.

Last winter this proved useful to get parts up above freezing and keep them there. Including melting the ice on used eyepieces.

Power consumption on this box is about 1amp from a 12V supply. For anti-dew in our current climate, power could be reduced. Perhaps I will switch out 1 resistor on the improved version?

A less robust, but more elegant solution would be to build this into a small flight, or instrument, or CD type case.

Anyone else gone for this approach, or anything like it?

[Hypernova]

What I'd like to see is something to keep the dew from forming on my finder 'scope. When the nights are humid like they have been this past week I have had problems with the front and rear lenses of my finder dewing up after the 'scope has been cooling for an hour or so. The front lens isn't much of a problem as it can covered when not in use and a dew shield can be fitted as well but the rear lens is totally exposed.

[tony4563]

Always strikes me why they design red dot finders like this.

You'd think they'd sort of extend the shields on the front and back just a little further to help resist dewing.

A nice idea would be a unit that incorporates internal heating elements so it would never be problem. All powered by an AA battery.

...I'm getting carried away aren't I ?

[Carbon Brush]

Extending the plastic moulding for low cost finder scopes, and red dot finders, would cost very little, and help dewing.

An AA cell keeping even an RDF warm is a bit of a problem. Unfortunately producing heat eats batteries. If you have a 'powertank' type product, or a car start-n-charge these often have 17 amp-hour batteries. In round figures the 12V battery will provide 1 amp for 17 hours. A serious observing session with my eyepiece box running permanently, but no power left for the mount!

The best you can do with AA cells is a tiny fraction of this. I have seen NiMH rechargeables that claim to have 2.5Ah capacity. Given that these produce on load 1.2 to 1.25V, around 1/10 of the powertank voltage, and about 1/7 of the Ah, you can easily work out that you have a tiny fraction (around 1/70) of the powertank energy available from 1 AA cell.

I'm emigrating to somewhere dry.

[starlady]

I just put a small box or part of an eyepiece bottlle over the finder eyepiece and rigel finder when I am not using them, I find that it is just enough to keep the dew off.