SCT primary mirror fogs up on my EdgeHD !?

Richard Carande:
Also, what sort of image artifacts, if any would you expect from these crystals?  Spikey stars?

Arny:
I keep my EdgHD SCT outside all year under a weather cover and so far had nonproblems. 

But last week after a freezing night and high humidity I noticed in the morning that the primary mirror had fogged up. 

a. How is this possible inside an almost entirely closed tube?
b. Has anyone made similiar experiences?
c. And how do I prevent this to happen?

Arny

John Hayes:
Add the fans and the Reflectix first to see how it works.  I doubt that you will need additional heat.

John Hayes:

Arny:
I keep my EdgHD SCT outside all year under a weather cover and so far had nonproblems. 

But last week after a freezing night and high humidity I noticed in the morning that the primary mirror had fogged up. 

a. How is this possible inside an almost entirely closed tube?
b. Has anyone made similiar experiences?
c. And how do I prevent this to happen?

Arny

This is not an uncommon problem with SCTs.  What is happening is that the telescope tube is radiation to the cold sky and getting pretty cold. In turn, that cools the primary mirror through radiative cooling as well.  Don't seal the vents, not only will that not work to prevent dew (and/or frost) but you will lose the opportunity to fix two things at once.  Instead, order a set of Tempest fans.  The are very small but also very effective at eliminating baffle plumes and at helping to maintain the interior of the telescope close to the outside ambient air temperature through convective heat exchange.  If you wrap the tube in Reflectix as well, you should not see any more dew or frost inside of the telescope.  

You can add a heat strap to the OTA and that will further guarantee freedom from dew but it's likely to be overkill and as you suggested, it can produce tube currents.  If you do add a strap, keep it on a VERY low setting.  Add the fans and the Reflectix first to see how it works.  I doubt that you will need additional heat.

John

Jan Erik Vallestad:
They look neat, but pricey. If I could run those off my Asiair it could be a viable option for me as well. Adding Reflectix is a rather cheap addition though as long as it's not creating reflection issues for nearby optics, and easily attached around all the upper losmandy.

Enda Kelly:

It's a bit of a paradox perhaps since bringing it inside would result in the same thing. I'm guessing an outdoor shed might be a good solution. I had the same happening to me as well recently while swapping the image train. Unfortunately mine had developed haze around the corrector plate after drying it off, so I'm about to clean it.

Any reccomendations on how to clean, as in, what to use? I have cleaned both my primary and corrector plate but can't seem to avoid leaving 'streaks' on the glass.