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Pier Height Vs. Wall Height?

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#1 Avi

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Posted 12 February 2010 - 12:09 PM

Quick question for everyone who has built an observatory.

How did you calculate your wall height versus your total pier height?

My observatory will be a standard framed wall height of 8ft.
I have a pier "stub/pad" that is about 3ft high from the floor.

If I were to mount right on the "stub" the viewing area available to me would be EXTREMELY limited.

Here's what I'm thinking:

I can do one of two things:

1.) frame in 4ft high drop down wall panels, which the wife is not keen on for "curb appeal" and other aesthetic reasons.

2.) install a mounting pier of an as yet unknown height on top of the "stub" to get the telescope closer to the top of the wall.


In regards to #2, is there some sort of guide for how far below wall height a telescope should be?
I figure the scope should probably be no more than 6 1/2 feet above the floor to ensure clearance from the roll off roof.

Thanks.

#2 Galaxyhunter

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Posted 12 February 2010 - 01:19 PM

The way I did mine. I had a fixed tripod & GEM mount. I knew that I wanted 8' walls. I setup the scope where I was going to build, Set the OTA to the lowest point (to tree tops)facing East, South, & West. From those directions I measured how high (or low) I need to make my knee (stationary) walls. It worked out htat mt East folding wall is 3' tall, & The South , Waet walls are 4' Fold.


1.) frame in 4ft high drop down wall panels, which the wife is not keen on for "curb appeal" and other aesthetic reasons.



Who is going to see the walls deployed in the middle of the night? Looking at my OBS, you wouldn't know that I have three walls that fold.

#3 Avi

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Posted 12 February 2010 - 01:30 PM

Carl,

We're going to stucco the observatory. The whole reason the observatory got approved was to be a practice run for the guest house we are building later this month/early March.

My idea was to frame from 2x4's a 6' wide by 4' high fold down panel, so it would be slightly recessed (rest of obs uses 2x6'es) and if done right, could be made to look no different than a window.

Yes, if it weren't for the stucco finish, I'm sure a thin hinge seam would be barely noticeable to anyone.

#4 Lorence

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Posted 12 February 2010 - 01:38 PM

I am building my observatory around the telescope. Not the other way around. My telescope is mounted at a height that is most suitable for my use.

The south wall is at 4', the side walls are 5'. There is about 2' of wall above the side walls that rolls back with the roof. With the roof closed the building looks like an 8 x 12 shed with 7' walls.

http://www.mts.net/~lmlod/ObPhoto1.jpg

That's a 6' ladder leaning against the wall. You can see the casters at about the 5' level and the roof at the 7' level.

Below is a photo of the roof section under construction to give you an idea how it was built. It's mostly 3/4" plywood. By the way it splits in half down the center. Not sure of the weight but I dragged each side out of the house and lifted them up onto the observatory myself.

http://www.mts.net/~lmlod/Roof.jpg

As for calculations.

telescope on tripod + tape measure = dimensions.



Lorence

#5 Avi

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Posted 12 February 2010 - 01:54 PM

Lorence,

That's actually a great idea for the roof.
I appreciate you sharing the info!

#6 mikey cee

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Posted 12 February 2010 - 02:41 PM

If you are using a refractor, sc or a cassegrain definitely go with option 2. If you store your scope horizontally you can clear the "ceiling" line by several inches just to be safe. At this level you can observe all of the atmosheric soup you like! If you have a reflector then you'll have to use a taller ladder. You should be able to sketch out rough scale drawings with measurements to easily see the results. I'd never just trust someones judgement who isn't directly involved. Because it not only is affected by height but also how far the center or pier is from the wall or walls of concern.:smirk:Mike

#7 Avi

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Posted 12 February 2010 - 02:50 PM

Mikey,

Thanks for the tips. I'll be using an 8" diameter Newt on a CGEM or atlas mount. Primarily using the rig for AP so not terribly concerned about EP placement

I would however like to have room to grow, hence why my observatory is 10x20 with half set aside for the telescope, and the pier "stub" is 18" diamater with a ten inch bolt pattern.

#8 Poconut

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Posted 12 February 2010 - 03:14 PM

The height your walls need to be would depend on how far the wall is away from the scope and also based on what angle you want to view at. If your scope is mounted so the visual path is 4 foot high at 0 degrees and the wall is 8 foot high and 4 feet away from the pier centerline; you would be limited to viewing at about 45 degrees or higher. If the 8 foot wall was 8 feet away, you would then be limited to about 22.5 degrees and higher (which is probably a reasonable minimum viewing angle).
Now if the scope is still 4' high and the wall is 4' away - you would want to make the wall 6 foot high to get the same 22.5 degree viewing angle.
I am being simplistic.

When viewing horizon through the scope, how high do you want the eyepiece to be? If you are 6' tall - 5' or lower would be a reasonable height. Subtract your mount height from that height to get your pier height.
After you get your desired pier height, then calculate how high your walls should be based on the distance from the pier and what minimum viewing angle you want to see.

Hope I wasn't too long winded. :)

#9 Avi

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Posted 12 February 2010 - 03:20 PM

Poconut,

Thanks! I figured I could sit down and figure it out with trig!
You gave me the "aha!" moment I needed.

Since I'm doing mostly AP work, I'm not terribly concerned with EP height.

#10 Poconut

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Posted 12 February 2010 - 07:09 PM

Things like houses, trees and high light pollution areas might also dictate higher walls or wall portions. No point in having a lower wall than necessary if a house is in your way, right?
I was going to bring up trig - but I am not familiar with my audience, so I wanted to keep it simple just in case. :p

#11 Buhlig

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Posted 13 February 2010 - 11:00 PM

I'll add my 2 cents worth. I did the trig based on the angle I thought was useable imaging above horizon..I think something like 30 degs above horizon. I also offset my pier from "dead middle" to give a little extra lower view towards my best skies. After building the obs, there were a few fortunate "lucks" i ran into. One was being able to test drive the mount with the roof closed (i have a ROR). Turned out, I lucked out that my ceiling joists were just right that I can slew anywhere with the roof closed with no issues...lucky. Also,if you plan to "park" the mount, you might think about what that position is or will need to be given your install height. In my situation, I need to put the tube on the side and lay it horizontal for the roof to open and close, mostly.

I was like you, I didn't care about visual at all, but I find on occasion, even the zero mag view finder is too high and I need a ladder to do the inital alignment. No way around that if you plan to see over the walls. And lately I've been trying planetary which requires a bit of visual help...my EP is like 10 ft in the air...again, no way around it.

Another advantage of a steel peir on the concrete is you can always change it down the road with a different steel peir...much easier than concrete. FYI: I had my peir welded up from a local weld shop for $200..so don't think it's really expensive. course, I did all the finishing work, but the material and labor to fabricate shouldn't scare you.

Sean

#12 Avi

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Posted 13 February 2010 - 11:17 PM

Thanks Sean.

I'm no stranger to a MIG/TIG rig, so building my pier should be a non-issue.
I think I'll be able to engineer the 6ft wide, 4ft high flip down panels and maintain a nice exterior view.

I'd love a telescoping pier, but there's no money in the budget for one right now. Maybe sometime down the road, but not any time in the next few years.

#13 wormstar

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Posted 14 February 2010 - 04:44 PM

I went with Pocnuts theory-I made the walls as high as I could and not have them be the limiting factor(I have trees and a shed to contend with), so 6' walls was perfect. It allowed me to go with a full height door(the north wall is 6'11 I think) its a Roll off roof and the roof rolls north.
Having a full size door is awesome-no ducking/banging scopes :)

#14 Lorence

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Posted 14 February 2010 - 08:23 PM

Same question on another forum brought out this URL.

http://astronomy.mdo...Wall_Height.pdf

Could be of interest to some around here.

Lorence

#15 Poconut

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Posted 15 February 2010 - 12:25 PM

I went with Pocnuts theory-I made the walls as high as I could and not have them be the limiting factor(I have trees and a shed to contend with), so 6' walls was perfect. It allowed me to go with a full height door(the north wall is 6'11 I think) its a Roll off roof and the roof rolls north.
Having a full size door is awesome-no ducking/banging scopes :)


I think that I saw somewhere that you tied your pier into existing bedrock? If so, just wondering how you are doing with vibration if your obs is built on top of the same slab. Or maybe you had an isolated single boulder where your pier is, I can't remember what I read exactly.
The reason I'm asking is that my entire property sits on top of a bedrock sheet and soil depths vary from 0" to 2 feet or so depending on the location.

#16 Poconut

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Posted 15 February 2010 - 12:35 PM

I think I'll be able to engineer the 6ft wide, 4ft high flip down panels and maintain a nice exterior view.


A few wide molding strips can be magic to conceal cuts for openings.

I'd love a telescoping pier, but there's no money in the budget for one right now. Maybe sometime down the road, but not any time in the next few years.

I wouldn't think a telescoping pier would be that good for AP, just due to the fact that the sections would have to be relatively loose fitted to adjust up/down. Just thinking about potential for vibration.

#17 Avi

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Posted 15 February 2010 - 12:40 PM

Good point, unless I spent tens of thousands on a telescoping pier, I'd imagine it would undo all the isolation I've done for the pier.

#18 Doug76

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Posted 15 February 2010 - 03:00 PM

6.5ft walls, 4.5ft pier, floor to top.

#19 Avi

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Posted 16 February 2010 - 09:28 AM

Doug, so by that math, roughly I'd be looking at a 6ft high pier with 8ft walls.

What's your viewing angle above the horizon before you hit the top of the wall?

#20 coopfore1

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Posted 16 February 2010 - 10:20 AM

My ob is also 10x20. warm room is 8x10and the scope room is 12x10. The walls are 6feet 6 inches high. There are 2 piers one is approx 4feet tall the other is 4.5 feet.Here is a pic of the front door....

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#21 coopfore1

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Posted 16 February 2010 - 10:27 AM

INSIDE

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#22 coopfore1

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Posted 16 February 2010 - 10:56 AM

Another inside with diff scopes and the roof rolled off...

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