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Equipment Discussions >> Reflectors

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Brian Albin
Seeker


Reged: 08/22/06

Loc: Western Oregon
Ground Clearance
      #5625002 - 01/15/13 07:19 PM

How much ground clearance do you like under an equatorially mounted Newton telescope?
I have read that the scopes need to be up some (the article did not say how much) to avoid something called ground currents. But that article was written in the days before electric fans were mounted on the back of the telescope tubes. Can we now bring our scopes down until they are sweeping the Earth to minimise eye piece height?


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azure1961p
Postmaster
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Reged: 01/17/09

Loc: USA
Re: Ground Clearance new [Re: Brian Albin]
      #5625285 - 01/15/13 10:00 PM

I don't know exactly how low you mean to go. My reflectors been anywhere from a foot to two feet off the ground pointing at the zenith. I don't kno if I'd go lower simply because I don't want plants up the tube fan or not. Too I don't know if the ground has currents per se, but there is ground level heat particularly important earlier than later in the evening.

Pete


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nytecam
Postmaster


Reged: 08/20/05

Loc: London UK
Re: Ground Clearance new [Re: Brian Albin]
      #5625651 - 01/16/13 05:12 AM

IMO you'll get a better response from a telescope forum than here

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Startraffic
professor emeritus
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Reged: 02/12/06

Loc: Lat. 39.143345, Long. -77.1748...
Re: Ground Clearance new [Re: Brian Albin]
      #5626031 - 01/16/13 11:21 AM

Brian,
I keep mine at the lowest possible height, but that's still 50"-60" off the ground. I have a fairly big mount. The fans I think you're talking about are there to help speed the cooling of the primary mirror and to reduce heat currents inside the tube. You're not sucking huge amounts of air up the tube. More like a very gentle airflow.

Clear Dark Skies
Startraffic
39.138274 -77.168898


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Tim Gilliland
professor emeritus


Reged: 03/28/09

Loc: Sand Springs Okla.
Re: Ground Clearance new [Re: Startraffic]
      #5626296 - 01/16/13 02:27 PM Attachment (10 downloads)

Mine is about 17' off the ground!

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Sarkikos
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Reged: 12/18/07

Loc: Scotophobe Maryland, USA
Re: Ground Clearance new [Re: Brian Albin]
      #5627866 - 01/17/13 11:18 AM

Brian,

Quote:

How much ground clearance do you like under an equatorially mounted Newton telescope?
I have read that the scopes need to be up some (the article did not say how much) to avoid something called ground currents. But that article was written in the days before electric fans were mounted on the back of the telescope tubes. Can we now bring our scopes down until they are sweeping the Earth to minimise eye piece height?




Sure. Just be sure to set up on grass - not asphalt paving or concrete. Throw a carpet underneath the scope and don't worry about it.

Mike


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Jon Isaacs
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Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: Ground Clearance new [Re: Brian Albin]
      #5627942 - 01/17/13 11:54 AM

Quote:

How much ground clearance do you like under an equatorially mounted Newton telescope?
I have read that the scopes need to be up some (the article did not say how much) to avoid something called ground currents. But that article was written in the days before electric fans were mounted on the back of the telescope tubes. Can we now bring our scopes down until they are sweeping the Earth to minimise eye piece height?




I think this is one of those things that is difficult to quantify but I am reluctant to bring it down too close. With my RV-6 which has no fan, but is always on grass, it does seem that sometimes the views deteriorate near the zenith, I don't know if it is because the scope is picking up my body heat somehow or if it's because the OTA is like a chimney, or maybe it's just coincidence.

Jon


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Brian Albin
Seeker


Reged: 08/22/06

Loc: Western Oregon
Re: Ground Clearance new [Re: Jon Isaacs]
      #5628204 - 01/17/13 02:34 PM

Thank you, everybody, for the replies.

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