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On Larger Observing Chairs.

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#1 Cotts

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Posted 12 October 2013 - 09:23 AM

My current observing chair, the "Stardust" (black metal with rungs and a seat on flexible rubber mounts is excellent when I use my 6" MakNewt or my 8" TEC scopes. Its range of seat heights matches these instruments perfectly. I intend to keep it forever.

BUT, my 16" Dob has a zenith eyepiece height of 78", forcing me to stand awkwardly to view which, in turn, causes back pain and the premature end to observing sessions.

I posted a thread here on my woes and I came to the decision that I need an observing chair, at least for now. Seated observing with this scope is what I'm after.

I got my tape measure out and came up with the following numbers:

My Stardust chair's highest seat height is 30", putting my eye at 64 ".

My dob's zenith eyepiece height is 78".

A little subtraction gives 14" as the height I have to make up, placing the seat height of my desired chair at 44", adjustable downward from that figure.

I am aware of the Starmaster 'chair'. and the Catsperch. The 'pro' model of the Catsperch gets within two inches of my target seat height. I have owned the 'Summit' and found it unsatisfactory for me, although it is an excellent product. See my thread, mentioned above, for details.

Anyway, after that lengthy preamble, I am asking for suggestions, designs, etc. for an observing chair which has a seat height of at least 44".

Have you any ideas of your own which might help? Pics and measurements would be great!

Or is there a commercial product out there of which I am unaware?

Thanks, CN community. I know you won't let me down....

Dave

#2 csa/montana

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Posted 12 October 2013 - 10:03 AM

A fellow CN'r & his son made this chair for me. I would think one could be made to any height, as long as the bottom supports were widened, so that it wouldn't tip over. I use this very comfortably with my 16". Off hand, I don't recall the total seat height of mine.

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#3 csa/montana

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Posted 12 October 2013 - 10:03 AM

.

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#4 gdd

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Posted 12 October 2013 - 10:37 AM

I don't have an adjustable observing chair yet, but noticed that if the chair is only a couple inches to short that my back really tenses up trying to reach the eyepiece. So, don't be satisfied with almost large enough.

Gale

#5 SteveG

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Posted 12 October 2013 - 02:50 PM

Very nice chair Carol!

#6 csa/montana

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Posted 12 October 2013 - 04:30 PM

Thanks Steve! It was a surprise gift for my new observatory!

#7 Jeff Morgan

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Posted 12 October 2013 - 05:46 PM

My dob's zenith eyepiece height is 78".


You might want to reconsider the requirement of reaching zenith.

Firstly, how much time do you really spend at zenith? If the answer is more than "very little" you picked a very fortunate latitude to live at!

Creating a limit of say, 80 degrees only creates a very small "hole" in the sky for you. Anything in that hole doesn't spend very long there. And you avoid the awkward motions of "Dobson's Hole".

True it will only gain you a couple of inches - but compared to a Stardust chair, the standard model CatsPerch chair gains you 12". Add the two together and you are just about where you said you wanted to be, and for a very small sacrifice.

#8 JimMo

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Posted 12 October 2013 - 06:08 PM

My dob's zenith eyepiece height is 78".


You might want to reconsider the requirement of reaching zenith.

Firstly, how much time do you really spend at zenith? If the answer is more than "very little" you picked a very fortunate latitude to live at!

Creating a limit of say, 80 degrees only creates a very small "hole" in the sky for you. Anything in that hole doesn't spend very long there. And you avoid the awkward motions of "Dobson's Hole".

True it will only gain you a couple of inches - but compared to a Stardust chair, the standard model CatsPerch chair gains you 12". Add the two together and you are just about where you said you wanted to be, and for a very small sacrifice.


This makes lots of sense. I really dislike mucking about at the zenith. I tend to avoid it although my dob's at a perfect height for flat footed observing. I do enjoy my adjustable chair, a catsperch clone, and I can't observe without it with my back.

Face it Dave, when you buy hockey equioment you need larger skates, a longer hockey stick, and a larger helmet. So in turn you need a larger scope to fit your size. If Mike Lockwood is at the WSP check out his fast dob(s). Awesome views, I remember a memorable view of Mars in IIRC in 2010 thru his smaller one, I don't remember the size and f/l but the view was the best I'd ever seen Mars.

#9 Cotts

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Posted 12 October 2013 - 09:30 PM

Trigonometry tells me the sin of 80 degrees is 0.985 which yields an eyepiece height of 76.8". 1.2" difference....

Using the zenith height is a convenient simplification only...

Dave

#10 Cotts

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Posted 12 October 2013 - 09:35 PM

I don't have an adjustable observing chair yet, but noticed that if the chair is only a couple inches to short that my back really tenses up trying to reach the eyepiece. So, don't be satisfied with almost large enough.

Gale


This is a very good point, Gale. Thanks.

Carol, that's a very nice looking chair. If you can, no rush at all, measure its highest seat height I would be most thankful... Since I would be using a chair on turf of some sort (No observatory) I would want much wider 'feet' both front and back for stability...

Dave

#11 csa/montana

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Posted 12 October 2013 - 10:12 PM

Dave, I'll get the measurement tomorrow.

#12 Jeff Morgan

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Posted 12 October 2013 - 11:14 PM

Trigonometry tells me the sin of 80 degrees is 0.985 which yields an eyepiece height of 76.8". 1.2" difference....

Using the zenith height is a convenient simplification only...

Dave


"A couple of inches" was just a WAG. Nice to see I was close.

#13 Pinbout

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Posted 13 October 2013 - 07:14 AM

I am asking for suggestions, designs, etc. for an observing chair which has a seat height of at least 44".



this should get you started

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#14 Cotts

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Posted 13 October 2013 - 08:48 AM

Hi, Danny. What a treat! I've downloaded the diagram.

Thanks!!

Dave

#15 mayidunk

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Posted 13 October 2013 - 12:44 PM

Is there any reason why you couldn't get the Catsperch Pro to get you 99% of the way there, and just sit on a pad, or even a phonebook to get you the rest of the way?

:question:

#16 ThreeD

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Posted 14 October 2013 - 01:02 AM

Hmmmm. My Catsperch Pro, which I built from kit two years ago, measures 46" from concrete floor to top of the wooden seat on the top setting. I don't think I've ever really used mine above about 33" when using my 16" dob but my scope must be shorter as I'm 6'1" and can view flat-footed at zenith.

#17 ThreeD

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Posted 14 October 2013 - 08:33 AM

I read the other thread where you had problems with the summit. I'm not sure your experience would be any different with the Pro or any style of chair that has an adjustable footrest/step for that matter.

The only time I've had a tipping problem is when I used my chair to sit while observing Omega Centauri. Being in Northern California, that means I was practically sitting on the ground and yes my weight was then forward of the front foot. I've never had a problem using the step as I typically don't need to use it to mount the chair anyway but when I do I suspect it is raised enough to also be behind the front foot.

#18 Bill Kocken

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Posted 14 October 2013 - 09:13 AM

I built my own chair, similar to Carol's, which is based on the Catsperch design. I specifically made it tall enough to use my 16"f4.5 at zenith, which I can do. I am 5 ft 9 inches tall, and I made my scope to be almost as short as possible. without the chair I can see through the eyepiece at zenith if I go on tip-toe.
To use the chair at the higher settings you need to get your self up into the chair which requires stepping on the footrest, pivoting around and then getting your posterior in place. I can do it, but I think it would be difficult for some people. When I am observing at the zenith, I often put the footrest at it's lowest position and stand on it.

#19 Jon Isaacs

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Posted 14 October 2013 - 10:07 AM

Creating a limit of say, 80 degrees only creates a very small "hole" in the sky for you. Anything in that hole doesn't spend very long there. And you avoid the awkward motions of "Dobson's Hole".



Jeff:

A while back I made some measurements of the eyepiece height versus elevation angle of my 16 inch F/4.42. Every scope has a different geometry, this one has the focuser angled at 33 degrees to the horizontal, so the results do not apply exactly. Still, the eyepiece height changes very little with elevation around the zenith because it's a sine function.

With an angled focuser, the eyepiece height increases slightly as you move away from the Zenith, at 90 degrees it was 68.5 inches, at 80 degrees it was 69.2 inches, 70 degrees, 69.3inches, it was not until 65 degrees that it had actually decreased.

With a horizontal focuser the situation better but still, I calculate for Dave's scope (if it has a horizontal eyepiece) with it's 78 inch eyepiece height, that at 75 degrees the eyepiece will be 76 inches, at 65 degrees it will be 73 inches. To use the standard Catsperch chair he needs about 6 inches or a 72 inch eyepiece height.

In response to Dave's previous thread on the subject, I spent some time carefully evaluating my Catsperch with I believe is the standard model. I am shorter than Dave, he's 6 foot 5, I am 6 foot even. Of course leg length versus upper body length enters here...

With my scope, to view at the Zenith, I never need to use the upper range of the seat height, that is above the pivot support (38 inch height) and climbing aboard the chair is quite easily done, that is as long as the chair is alongside the scope rather than facing it.. Dave was having problems with the Catsperch Summit flipping while mounting it, I had no such problem with the standard chair.

Some more math.. The Catsperch Pro has a seat height of 46 inches, Dave's scope has a maximum eyepiece height of 78 inches, a difference of 32 inches.. I am using my chair at 38 inches height and the maximum eyepiece height is almost 70inches.. again about 32inches.. Maybe Dave has longer legs than I do..

Bottom line:

I do think that it's important to be able to view in the region of the zenith because of the geometry means losing just a few inches means losing a significant part of the the sky.. the best part of the sky..

There's a reason that most 16 inch Dobs are about 4.5 rather than F/5, that's about 8 inches of eyepiece height and that's a lot...

Jon

#20 Cotts

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Posted 14 October 2013 - 02:11 PM

I've done some math, too.

Scope Angle Actual focuser height at center of opening.
90 (Zenith)---------78
80----------------77.5
70----------------75.5
60----------------71.5
50----------------67.5
40----------------61
30----------------53.5
20----------------45.5

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....

The distance from my bottom to my eyes while sitting comfortably upright is 34" (Yess, my legs are quite long. My upper body is of a man 6'2" or so, my legs are ridiculous...)

The seat height of about 44-46 inches is correct. I'm leaning now to the Starmaster-style 'chair' It appears to be less tippy and can easily be scaled up to the appropriate height while still folding flat for transport....

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'm going to make some sketches to visualize such a chair.....

Thanks, everyone for the excellent feedback...

Dave

#21 Jeff Morgan

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Posted 14 October 2013 - 03:31 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.

#22 Bill Weir

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Posted 14 October 2013 - 08:59 PM

My friend Guy built this chair. http://www.members.s...e/GuysPerch.htm
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.

Bill

#23 Jon Isaacs

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Posted 14 October 2013 - 09:54 PM

I've done some math, too.

Scope Angle Actual focuser height at center of opening.
90 (Zenith)---------78
80----------------77.5
70----------------75.5
60----------------71.5
50----------------67.5
40----------------61
30----------------53.5
20----------------45.5

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...



Dave:

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.

Jon

#24 Cotts

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Posted 15 October 2013 - 08:44 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...

Dave






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