equlibrium of your scope

[a10ken]

Hi all. can someone please explane why you would let your scope cool for a few hours to match the ambudent temp and then induce heat via a dew strip heater, and if you do then how does this affect the seeing?

still not sure what way to go to prevent dew forming.

thanks folks:icon_salut:

[E621Keith]

I am not sure how dew heater will affect the image quality, but my guess is the temperature difference is small enough that it would not cause a significant degradation in image quality. That, or the image degradation from thermal current is far less than that from dewed up optics, and people are willing to sacrifices a little bit of image quality to prevent dew building up.

Your optics when taken out of a warm house can be tens of degrees warmer than the ambient. This temperature gradient will produce much more turbulent than the heater strips that only a little bit warmer.

Of course I can be all wrong, so please correct me if that's the case

[brantuk]

The idea is to set the temperature of the dew strip slightly above the dew point so dew can't form on the objective lens. The rest of the scope should stay at ambient temperature if you get it right. You might need to experiment if you're new to dew strips and controllers

[a10ken]

Thanks guys. what is the temp of the dew point or does it vary with local conditions.?

[Merlin66]

The Dewpoint temperature varies with the humidity.

A bit of trial and error is called for. Just enough warmth to keep the lens clear of mist/ dew.

We're only talking about a degree or so difference to ambient - it doesn't have any significant impact on the image quality.

[a10ken]

Ta thats what i wanted to know. my scope is a 10" newt so where exactly would the heaters go

[Merlin66]

On a Newtonian the only parts likely to be affected by dew are the secondary mirror or the eyepieces themselves...

You could fit just an extended dew shield to the front of the tube to give some additional protection to the secondary.

When you use a refractor or SCT the dewing of the front lens becomes a major issue - then you need a dew heater around the lens.