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Hi, Can anyone tell me what length I need to make a dewshield for a 10" Dobsonian please? :o

Is there a correct length per size of scope for dew shields? ;)

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I've heard that the recommended length is twice the diameter of the primary mirror. Mine (bought) projects about 12" above the top of the tube of my 10" newtonian and seems to work well enough.

Dew is not a problem for me but stray light is - the main function of my shield is as a light shield.

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John,

Thanks for your advice. I have a problem with dew and light ;)

I will make one this weekend, and see how it goes.

Cheers!

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It's often said that a dewshield should be twice the length of the aperture.

With SCTs, Maks & refractors, thats probably a good idea. But with a Newtonian

we are not trying to protect a large piece of glass pointing at the sky.

The Newtonian secondary is much smaller, is some distance down the tube,

and facing the other way. So I think that shorter is ok. It does help to combat

stray light, but I made mine to help with occasional dewing of the secondary

on very damp nights.

Best regards, Ed.

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I made my dew shield from black camping mat and velcro. It does the job fine for stray light and dew. It's double the length of the diameter of the primary

Edited by MissMessier

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