Don’t play misty for me!

[Moonshed]

I have a Celestron 8” and like all SCTs the corrector plate can mist over at times and ruin observations. I have a Revelation Dew Heater I purchased 4 years ago that usually does the job. Sometimes though, like last night, it is not up to the job. After around 2 hours the corrector plate was something like 20% misted over. I do keep a hairdryer close to hand for removing condensation from the Telrad and when desperate will use it on the corrector  plate for a quick fix, but worry this will cause turbulence within the tube.

I take my scope out of the shed and switch on the dew heater at least an hour before using it. Last night was colder than it has been, about 4C I think. I didn’t use the dew shield but even when I do it doesn’t necessarily stop any misting.

Does anyone have a solution? Do I need to add another Dew Heater or are there more powerful ones I don’t know of?

Edited November 20, 2020 by Moonshed

[wimvb]

I assume that you also have a dew shield? The combination of shield and heater keeps dew off my maknewt, even if all else is dripping wet.

[Moonshed]

21 minutes ago, wimvb said:

I assume that you also have a dew shield? The combination of shield and heater keeps dew off my maknewt, even if all else is dripping wet.

Yes, I do have a dew/light shield that I almost always use but even so the lens will still mist over after a short period of observing, the higher up the scope is aimed the quicker it mists over.  If I leave it parked for a while in a horizontal position it will not mist over, it’s only when pointing upwards to anything over say 45 degrees the problem develops.

[dweller25]

You could try wrapping your SCT with Reflectix and extending your dew shield with a cheap foam camping mat

Edited December 13, 2020 by dweller25

[Luke]

I used a Kendrick dew heater (plus a dew shield) with a C11 many times for imaging and never had problems with dew (apart from when I forgot to turn the heater on!!!).

These days I have an 8 inch SCT and always use the dew shield. I don't bother with the heater for shorter sessions.

Edited December 13, 2020 by Luke