Expert: Jayendra Upadhye - 11/15/2008

Question
What is the best way to control humidity without heat?  Would blowing air through a desiccated chamber into/on your lens offer any control? This is a big problem for me.  Your suggestion(s) would be appreciated....Thanks

Answer
Hi,
Found this one on the question pool.

Seer! One cant afford to be so laconic regarding questions of this type!! Why the brevity?
You see one needs to explain to the expert which lens it is you are worried about.
The objective or the eye piece?

Obviously if the humidity is so high it occults your vision by drop formation, smudging the eyepiece, nothing can be done!

If it is the objective lens you are worried about (fogging), then :-
1 - Just warming the equipment (not heating) by several degrees above ambient, by say leaving the telescope near the radiator or fire place, will help you for a time.

2 - If you have a motorized telescope and are doing long term readings (two hour exposures and so on), you really need to do things, like passing desiccated air over the objective. The constant air flow will ensure moisture removal.
Though implementing this will be involved and tricky.

I have a simple solution that DOES involve heat, but it is simple and elegant and so inexpensive, you are going to laugh!

Ofcourse it is highly unconventional to say the least.

Just use a hot hair drier, (battery operated is best, if there is such a thing), point it from a distance of about a foot, at the scope in general and the objective area in particular and apply "gentle heat" to the scope.
It will mainly make fog on the lens disappear! And once the scope is "warm", keep that fogginess away for quite a while.

Please do rate the answer if you find it helpful.
regards.
Jayen