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Old 18-08-2020, 04:08 PM
Ittaku (Con)
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Dew questions

Hi all. I'm trying to figure out the best application of the (passive) dewshield on my CST with these cold nights.



Should the padded bit go over the tube?
Should the shield hang out as much as possible?
When leaving the scope out for a couple of hours before using it (with the cover on) is there any point applying the dew shield at that time?
Is there any point wrapping the OTA proximal to the dewshield with something insulating, like a kitchen towel?

Also when bringing the scope in at the end of a night's viewing, should I leave the cover off for any dew to evaporate?
Are the little heated strips worth using, if power isn't a problem?
Any other hints?



Thanks!
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Old 18-08-2020, 05:03 PM
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mental4astro (Alexander)
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Hi Con,

For an SCT and Mak, and also refractors, there is a way of protecting the scope from dew and a way that allows you to use the scope WITHOUT needing to wait for it to cool down:

SCT and Mak total dew control without heat -a solution

A dewshield alone will not totally stop dew formation. Insulating the OTA will also extend the dew free period. But if dew formation conditions are heavy enough, then dew will form, and you will need a way to prevent dew from forming or drying it off. And of course, there will also be nights when dew won't form.

Alex.
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Old 18-08-2020, 05:31 PM
Ittaku (Con)
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Quote:
Originally Posted by mental4astro View Post
For an SCT and Mak, and also refractors, there is a way of protecting the scope from dew and a way that allows you to use the scope WITHOUT needing to wait for it to cool down:

SCT and Mak total dew control without heat -a solution

A dewshield alone will not totally stop dew formation. Insulating the OTA will also extend the dew free period. But if dew formation conditions are heavy enough, then dew will form, and you will need a way to prevent dew from forming or drying it off. And of course, there will also be nights when dew won't form.
I like it. Will consider in future, thanks.
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Old 18-08-2020, 11:40 PM
Renato1 (Renato)
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I used to have resistors attached inside my dewshield of my SCT. It worked okay, but I still had the problem of eyepieces, finderscope and Telrad dewing over, on which I was using a 12 volt hairdryer plugged into a power pack.

I don't do astrophotography, so nowadays I just use a 12 volt hairdryer plugged into my Projecta battery starter and blow the dew off all of them. Obviously, I have to do it more frequently on more dewy nights.

Only problem I rang into was that some power packs wouldn't power the hair dryer through their 12 Volt sockets, so back then had to rig the wires of a 12 volt socket extension lead to jumper cables.

Mine is not an elgant solution - but it's quick - and the 12 volt hairdryers don't cost much on Ebay.
Regards,
Renato

Last edited by Renato1; 19-08-2020 at 01:01 AM.
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Old 19-08-2020, 09:37 AM
morls (Stephen)
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In my experience, the solution described by Alex works a treat for my Mak. Since making an insulation jacket/dewshield from Kingspan aircell (genereously provided by a fellow IIS'er) I've never had to wait for the scope to cool before observing, and have had minimal dew issues.

It works.
Beautifully.
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Old 19-08-2020, 10:25 AM
Ittaku (Con)
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Sounds good. I just unpackaged a delivery I received and realised that bubble wrap might be a good insulator too.
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Old 19-08-2020, 01:26 PM
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multiweb (Marc)
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Quote:
Originally Posted by Ittaku View Post
Sounds good. I just unpackaged a delivery I received and realised that bubble wrap might be a good insulator too.
You can get some silver foil bubble wrap on ebay. Works a treat.
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