Eyeball fogging

There was an interesting question brought up on the Tak LE thread, but it didn't get answered there:

Will an eyepiece dew heater also prevent (or reduce) eyeball fogging, or are they only effective on dew resulting from heat-loss due to open sky exposure?

What, your eyeballs fog?!

Dmitri

Jeff,

I posted that and responses didn't go far. I'm going to try it on the Tak group here and at yahoo. Will let you know.

P.S. Dmitri is the resident comedian

Steve O.

Well, the eye is surrounded by a layer of air with elevated humidity. Due to this fact, the dew point temperature near the eye is higher than in the ambient air. This manifests itself in dewing of the eyepiece in a proximity of the eye.

If you rise the temperature of the glass, by a heater or by holding the eyepiece in a warm pocket, you might place its temperature above the dewpoint of the ambient air, but it might still be below the dew point in the eye's own "atmosphere". If you warm the glass yet more, the dew point will shift yet higher and the dew will not fall even near the eyeball.

This hopefully makes it clear that it you make the eyepiece warm enough, the dew will not appear on it no matter what.

Dmitri

EP heaters will pretty well solve any problems with fogging or dew.

I have never had an eyepiece fog that was protected with a Kendrick dew strip. As long as the glass stays at least 1° above C ambient you are ok and eps are easier to keep stabilized than most other optics.

Randy

Hi Jeff...

I was the one who posted that comment re: the LE's fogging due to "eyeball heat/humidity".
It can be reduced by folding down the rubber eyecups and eliminated by eyepiece heaters...but,in my location (Florida) the heat had to be turned up rather high. So much so that it induced some "seeing" effects of its' own!
This will vary depending upon your local conditions.

Thanks everyone for the replies. Now all I have to do is wait for the movers (now 3 weeks late) to turn up with my scope.

-- Jeff.