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Equipment Discussions >> Equipment

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Jeff Morgan

Reged: 09/28/03

Loc: Prescott, AZ
Re: On Larger Observing Chairs. new [Re: Cotts]
      #6137407 - 10/14/13 04:31 PM


Jon, I agree with your point about viewing near the zenith. My SErvo-cat actually makes observing up there much easier than manual. It tracks for me so I do not have to worry about the difficulties of "Dobson's Hole."

I didn't know you could do that ... guess I'll be changing some of my Argo Navis defaults next session.

Very cool.

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Bill Weir
Carpal Tunnel

Reged: 06/01/04

Loc: Metchosin (Victoria), Canada
Re: On Larger Observing Chairs. new [Re: Jeff Morgan]
      #6137945 - 10/14/13 09:59 PM

My friend Guy built this chair.
I like how he added the eyepiece rack to the seat. On this page is a link to actual plans. He built this chair to be right for him to observe seated with a f/4.5 16" dob that he built to standard Obsession dimensions. Guy is not tall.


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Jon Isaacs

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: On Larger Observing Chairs. new [Re: Cotts]
      #6138025 - 10/14/13 10:54 PM


I've done some math, too.

Scope Angle Actual focuser height at center of opening.
90 (Zenith)---------78

MY focuser is mounted to tilt up a bit so the actual eyepiece height will be slightly higher than above if I use long ones like Ethos. But I doubt it would be even 1/2 inch... Also, this effect only comes in to play when the scope is pointed very low...


Did you actually measure this or did you use 3-D geometry to solve the problem? Do you use a Paracorr? All that adds up..

I measure my scope. With its the 33 degree eyepiece angle, the Paracorr and a 32mm TV Widefield, the eyepiece height increased from 68.5inches at the zenith to 69.5 inches at 80 degrees and was greater than 68.5inches all the way down to 65 degree inclination.

Angle Focuser Paracorr+32mm
(deg) (inch) (inch)
90--- 68.5--- 68.5
80--- 69.2--- 69.5
70--- 69.3--- 69.5
65--- 67.3--- 68.5
60--- 66.2--- 67.8
55--- 65.0--- 66.4
50--- 63.0--- 65.0
45--- 61.0--- 62.6
40--- 58.8--- 60.4
30--- 53.5--- 55.4
20--- 47.5--- 49.0
10--- 40.7--- 42.4
5---- 37.2--- 29.5

I much prefer an angled eyepiece because my primary dark sky spot is open to the south and objects like Omega Centauri, Omega Centauri and Omega Centauri culminate at 10 degrees.. I like to be comfortable viewing near the horizon.


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Just Wondering

Reged: 10/10/05

Loc: Toronto, Ontario
Re: On Larger Observing Chairs. new [Re: Jon Isaacs]
      #6138651 - 10/15/13 09:44 AM

Jon, my measurements were made to the center of the empty focuser. I do use a Type 1 Paracorr. I could re-do the measurements with it and a 17 Ethos eyepiece - do you think it would add any more than an inch?

I can't do it today...


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