Dew Control

[david o]

Hi all,

If all goes well I'll soon be getting a SW Skymax 180 Pro Mak-Cass scope.

Realizing that it'll need some sort of dew control I'd like advice on what to get.

Would a dew shield on its own be enough, or will it need one combined with a heater strip?

Of the different dew heater systems & controllers available what brands/models are good? AstroZap? Kendrick?

Thanks in advance an clear skies

[The Warthog]

I have an 8" deep dew shield on my 4" refractor, and amm not often bothered by dew, nor on the mirror of my Newtonian, but eyepieces, finder, and teh secondary mirror are another matter entirely. I am considering getting the Kendrick dew removal system to protect this part of my kit, as I've often had to cut oberving nights short. You can make a dew shield for your catadioptric out of many materials, but eps will always be a problem.

[david o]

Thanks for the pointers Warthog.

Long time, no see - welcome back.

Hope you get clear skies soon.

[John]

With the mak-newt design you have glass right at the top end of the scope so I think you will need similar arrangements to those used by schmidt-cassegrain users. When I had an 8" SCT I found a heated dew strip worked well enough on most nights but occasionally I needed a dew shield as well. I think my heated strip was an Astrozap.

Of course you can get these systems that run several dew strips, one for the meniscus, one for the finder and one for the eyepiece.

[david o]

Cheers John,

Suspected as much about the meniscus lens.

Clear skies

[brianb]

The corrector plate on a Mak is thick and has quite a lot of thermal inertia. This has two effects: (1) the scope takes a long time to cool, (2) it won't dew up as fast as a similarly sized SCT with a thin corrector plate.

If your observing sessions are reasonably short (2-3 hours) you'll probably get away with a dew cap, especially one made from camping mat foam that's at least twice as long as the diameter of the aperture. If you want to be able to observe for longer than that, an active dew control system will almost certainly be needed - on at least half the nights in the UK.

[david o]

Thanks Brian,

Couple of good points there, especially the necessary dimensions for a dew shield.

[Macavity]

Well I hope (availability willing) to try at least a basic 2-chan controller and heating strip. But I might now retain my (at first supposed, overly) long camper-mat dew shields - As is. Now, if only I would remember to hold my breath, when viewing though the finder scope... and then returning to a well steamed-up eyepiece.