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How and when do you use the fan?

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#1 w0mbat



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Posted 11 October 2013 - 12:12 AM

Hi all,
Soon I will be trying my first images with my N10. I have never owned a telescope with a fan before.
So I would like to know how and when experienced users operate their fans. Is it just for temperature equalisation before imaging? Or do you run them during imaging?
My N10 fan is very noisy at full speed. I wondered if this would introduce some vibration in the OTA. This led me to wonder what others do.

ASA DDM60Pro, ASA N10 Astrograph, Orion ED102T CF Refractor, Canon 60Da DSLR, Sirius 2.3 Metre Observatory, WIN10 Pro 64bit.

#2 Michip



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Posted 11 October 2013 - 06:47 AM

Hi Ian,


My C14 has also installed fans, therefore I was looking around the web to find some information when to use them. What I can clearly say is, don't use them on full speed while you are imaging. Most people seem to use fans to cool down the mirror to the surrounding temperature. While imaging, it's difficult to decide how to use them. There are several planet photographer who are saying that it's much better to keep the fans running slow to improve tube seeing and to become a better resolution. I think this may take effect when you are imaging planets, but not on long exposures.


I would recommend to keep them running slow while imaging, so the mirror will faster adapt the surrounding temperature, especially when the temperature are falling faster due to cold front.




PS: Happy Birthday :)

Edited by Michip, 11 October 2013 - 06:49 AM.

#3 mattssporre



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Posted 13 October 2013 - 09:42 AM

Hello Ian,


I use the fans to prevent dew from forming on the primary mirror. Where I live the humidity is a real problem in the fall when temperature starts to drop in the nights. One would think that the long tube would prevent the dew formation - but that is not so. From August I use the fan on 1-2 steps lower than max. From December or so most of the water is out of the air and I can go without the fans if I would like, but the fans not seem to do any harm so I usually leave them on.



#4 MarkS



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Posted 14 October 2013 - 07:12 AM

Hi Ian,


I have been running the fan all the time - it's been pretty dewy at my site. I've seen no problems.



Edited by MarkS, 14 October 2013 - 07:12 AM.

#5 MarkS



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Posted 04 February 2014 - 08:04 AM

Following up on this, I have experienced some horrendous dew conditions this summer near the coast - ~100%RH at a temperature of 25C.


The fan running flat out plus a Celestron 11" dew hood  has kept the condensation at bay! And 5min subs look fine.



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