Dew or no dew? Silly question from a newbie!

[Hemi]

Dear members,

I live in the tropics (as all those who've read my endless questions will know), Darwin to be precise and repetitive! All I read about is how bad the dew is up here because of the humidity.
I bought a dew shield but haven't used it yet (3 months) as I don't seem to get due. The air is near saturated this time of year, but the due point here is always 2-3 degrees away, and as temps are very stable at night here, I don't think I get to the dew point.

Is that right? What does the view actually look like when there is dew? How can I tell?

Thanks for the patience!...and answers!

[mental4astro]

Hemi,

Being in Darwin, you've seen how the windows of air conditioned places fog up during the wet - that's what dew looks like. And the effect of looking through a fogged up scope is the same as looking through a fogged up window - crap, :rolleyes:

Many factors affect the formation of dew, not just the 'dew point'. The lay of the land for one. If you are set up on lush turf/agricultural land, dew forms more readily as there will be more moisture released into the air from the soil and turf. The topography - a valley will fog up, but the ridges of the valley will remain clear. Wind will prevent dew from forming, and dry it off too if it has formed on a surface.

Alex.

[AEAJR]

Hemi,

I presume you store your scope somewhere outside or your storage location is not air conditioned. If the scope were cool from being in AC and you took it outside to a high humidity area the glass would fog up.

If you are outside and the temp drops below the dew point, the glass would fog up.

I don't have a lot of problems with dew but I do have problems with streetlights. I use the dew shield to help shade the lens of my refractor, or the secondary mirror of my reflector so that I don't get dew or frost when the temp drops below freezing.

BTW, I also have a small, cheap, 12V hair dryer that can defog the eyepiece if it fogs up. Could use that on any glass. Doesn't get very warm and probably near useless for drying hair but it works for this purpose.

[Cosmic]

You will know, when the sub looks...frosty :lol: It creeps in slowly. I just made a dew strap from resistors, easy to make or buy if you need it. I only use one because my dslr sits in cooler.

[Hemi]

Thanks all

Yes I keep my scope indoors in a non air conditioned room next to my observing spot. There's little to no temp difference, so I do t have to wait for the optics to get aclimatised. I think it will be different in the dry season.