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Hi all, I have recently bought an 8-inch dob and was wondering whether dew will be a problem with these  scopes. At the moment i am only using it in the evenings until about 2 am and haven't had a problem yet. Thanks in advance. 

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1 hour ago, KeithP22 said:

Hi all, I have recently bought an 8-inch dob and was wondering whether dew will be a problem with these  scopes. At the moment i am only using it in the evenings until about 2 am and haven't had a problem yet. Thanks in advance. 

You probably may experience some dew forming around the secondary mirror if coming from a warm room inside the house to outside where the air is cooler. Allowing the OTA to acclimatise for a few minutes before viewing, unless stored in a garage/shed/outbuilding. Adding a dew shield is a must accessory if you own a Makustov, SCT, Kletsov, Maksutov-Newtonian, open truss tube, etc., though these are/can be more expensive than the conventional Newtonian/Dobsonian OTA.

I allow thirty to forty minutes for my Mak. & SCT before viewing to acclimatise with a dew dew shield attached. When I have finished viewing and back inside, I leave all caps off and let them dry out naturally before refitting while I am resting/sleeping. If you smoke, try and place in a room where the smoke/fumes will not interfere or settle upon the optical surfaces.

 

49 minutes ago, KeithP22 said:

Thanks Terry. What part of the OTA would this fit around. Do you need to power it up or does it work without power.Totally new to all this. 

You can get heated dew bands that wrap around the outside of the OTA near the primary mirror, and eyepieces, etc., or for Mak's. and SCT's, etc., heated or un-heated dew shields that wrap around the OTA near the meniscus cell [Mak.] or corrector plate [SCT].

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58 minutes ago, KeithP22 said:

Thanks Terry. What part of the OTA would this fit around. Do you need to power it up or does it work without power.Totally new to all this. 

Totally unpowered. It simply fits to the aperture end of the scope. Its about 300mm long and comes pre-fitted with velcro and an attached liner that appears to be felt. I got the  8" Cele Edge HD:  £34 and it fits great to my Skywatcher 200p. The only thing that is likely to dew up is the secondary mirror and this actually delays that considerably. You will probably be too tired by the time it dews up when fitted with this.

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I generally find that it’s the EP and finder that dew up. The secondary only dews is there is a lot of moisture in the air.

Yoy can buy secondary heaters from Kendrick, Google search.

You can make a dew  shield for the front of the scope from a foam camping mat, if you go to a haberdashery you can purchase sticky backed Velcro to line the mating edges of the said homemade dew shield.

I also fitted a fan to the base of my dob to keep the primary mirror dew free. A computer fan is perfect and depending what Dob you have, there may well be holes in the mirror supports that match perfectly with the hole spacing On the computer fan.

If you have the primary fan, EP dew band and finder dew band you could get away with a 17Ah battery, which should give you two nights viewing.

Edited by Uplooker
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Of course when the wifes outside with me, giving out about the price of this and the cost of that.  The skies are this, that and the others a waste of time, creates a warm ambient atmosphere around, thus negating any dew! 🙂

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