Dew on 190MN primary mirror.

[Gunnar]

Hi.

I have this problem. Dew coming up on my Skywatcher MN190 primary mirror a few times despite it`s a closed tube. Is it recomendable to put a dewstrip around the tube at the primary end or will this cause thermal issues inside the tube?

Gunnar

[andrew s]

Gunnar - I would get some Silica gel and make a plug(s) to fit your focuser. Put this in when not in use to get the internals moisture free. Do it in a warm room if you can.

Once you have done this always keep the tube closed by keeping the plug/camera or eye peice in the focuser tube.

Hope this helps Andrew

[Gunnar]

Thanks for the tip Andrew.

[barkis]

Dewing is a nuisance, and affects most telescope optics, and externals to the point where even your OTA can drip water.

You can combat it with dew straps, both top and bottom of the scope, to protect the corrector and secondary, and the primary.

A couple of dew straps around the base of the tube should help, but careful control of their temperatures is needed. Ater all, you only need the mirror to be slightly higher than ambient to prevent moisture forming. A dew shield can also be used, but I'm not sure a custom one is available, so you may need to make one yourself.

A camping mat is the usual material for such a project.

A bit of experimenting will be required to get things just right, but even then, varying conditions will dictate what is required.

Err on the side of very low dew strap temperatures, and work your way up gradually if necessary If you have, or get a multi outlet controller, make notes of the settings that work well under any prevailng conditions. So at certain air temperatures, you will gain knowledge of what controller settings work best at keeping your optics dew free.

Ron.