How Do You Prevent Telescope Lenses from Fogging Up in Humid Climates?

[kurushio95]

...is not fun. I have a telescope that I got when I was a lot younger. A nice (I think) little beginner telescope, a Meade Polaris 60mm. Anyway, my problem is the humidity where I live. I live in Louisiana. Everytime there's a clear night and I decide to go try and do a bit of looking, to try and get into astronomy, the lens fogs up like no one's business. Does anyone else have this problem? How'd you deal with it?

Also, can anyone point me in the direction of a good astronomy forum (besides this one...I always get distracted by the other boards and always get put in my place with my rudimentary knowledge of astrophysics).

 

[Gokul43201]

You need a dew remover: http://www.kendrickastro.com/astro/index.html

 

[chemisttree]

You can use a hair dryer if you have 120V handy. Use brief blasts of warm air. Should be fine for your scope.

 

[russ_watters]

It is a big problem for me. I have a big telescope (11") and even with my dew heater on, in the fall I still get covered with it eventually. But the dew heater does help.

 

[Chronos]

Let the instrument acclimitize itself a few hours before use. A few minutes with a hair dryer will suffice after that.

 

[russ_watters]

No, it won't. Telescopes radiate heat into space just like any other object. And just like your car, the equilibrium temperature of the interior of the telescope is below ambient temperature, causing condensation well before you even see dew forming on the ground.

 

[chemisttree]

It works for me.

 

[russ_watters]

Sorry, I didn't read the second part - what I meant was that acclimation doesn't help, it hurts the situation as far as dew goes (assuming it is cooler outside than inside). Sure, a hairdryer will help get rid of dew that has formed.

 

[chemisttree]

Actually, with a cheap 60 mm scope, heat effects (taking it out from a warm room into the cool night air) probably wouldn't affect what you could see through it too much. Larger scopes with more mass and dimension used to take long exposure images would certainly suffer from not being acclimatized and doing so would make it much more susceptible to dew formation.

 

[Chronos]

Acclimatization is not a huge issue with small [<6"] aperatures, but is an issue with larger instruments. Most people keep their scopes indoors when not in use - not a bad thing. But when anticipating an observing session, it is a good idea to let them breath in the great outdoors for a few hours. The hair dryer routine is merely a time saver and should not be overdone. Cease drying as soon as the condensation evaporates. I do understand Russ's point on that count. It is not a good idea to heat optical surfaces more than necessary to defog them.

 

[kurushio95]

I'm taking it from a cool, dry environment (my house) to a warm, humid environment. I'll try setting it on the back porch in the morning then look through it at night and see if that helps.