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kestrel0222
Carpal Tunnel
Reged: 05/21/06
Posts: 2338
Loc: Milford, Michigan
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The digital compass (in my opinion) is not accurate enough to be used for astronomical targeting. I still rely on my manual setting circles with my Wixey digital angle finder. This seems to be a pretty good match.
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Tom
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csa/montana
Den Mother
Reged: 05/14/05
Posts: 39594
Loc: montana
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Mike: Why is the magnetic compass important to you? Once you center Polaris, adjust your Azimuth scale needle to zero, you are ready to go! If using the digital inclinometer, I don't even have to level the scope. Rarely, is an object completely out of the view, & when it is, it's because I got sloppy on setting the degree needle.
It sounds difficult, & yet it sounds so simple that one thinks, no way can this work; but it does, indeed work beautifully.
I appreciate everyone's input to this thread, it's been a great help to all! 
Carol
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
DreamCatcher Dobservatory, #2
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 897
Loc: Iowa
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I have to agree with Tom, it is pretty hard to beat the accuracy of a 20" dial that you can buy for about $10 - no batteries, no magnetic interference from metal scope parts, no worries about magnetic declination.
Tom's Wixey inclinometer at $40 is a great value too, less than half the cost of the SmartTool that I used.
A $50 system with electronic altitude accurate to .1 and azimuth accurate to (conservatively) a half degree is a very cheap and precise set up- less than half the cost of encoders alone for a DSC system!
Rod
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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lerock
sage
Reged: 03/23/06
Posts: 311
Loc: Arizona Coast
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I too have the Wixey & setting circles. but with a compass you would not have to worry about finding north, you could just drop it & go, much like you do with the Wixey. I'm very lazy, I'm always looking for the easest way to do something. But, at least for cheap money, the compasses arn't their yet. I'll break down & buy the Tech 2000 drive system, it motorizes the dob & the motors have built in encoders for about $700, but that is not what this thread is all about. Thank you Carol, this is a very good thread...
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Mike
18" f4.5 Obsession #1377
W/Argo Navis DSC
6" f/10 ANRA Canopus, circa 1963, modified for solar
If you don't make dust, You eat it.....
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Beri
sage
Reged: 06/29/05
Posts: 294
Loc: Croatia
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Quote:
If using the digital inclinometer, I don't even have to level the scope.
Well, this is not completely true. Depending on the relations of the aim of the scope (or to be precise, the inclinometer), and the inclination of the base, errors are larger as you get near zenith..
For example, the scope is pointed due North, and the base is tilted, low on the east, high on west.
When the tube is horizontal, the error is 0. But as you rise the tube, since the axis of the altitude bearings is tilted, the scope will point a few degrees to the NE, allthough both the azimuth and altitude scale tell you that the scope is pointed at Polaris...
Same situation, the scope pointed due east or due west, you will not get any error when using a inclinometer, because the altitude axis is parallel with the ground
When I carefully level the scope, I always get the desired object inside a 1º field, using both az and alt scales printed on paper...
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15x70 Binoculars
10" truss Dob
http://www.scopemaking.net
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csa/montana
Den Mother
Reged: 05/14/05
Posts: 39594
Loc: montana
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Using a scale without a level base is problematic because while you can always set the scale to match an inclinometer determined setting, when you turn the rocker on the base, the scale reading will be off immediately and will not be exactly accurate until you return it to the same azimuth you set it at.
Now, depending in the degree of deviation from level, this error could be small, but it could also be very large and make finding things in a one degree or so field of view very difficult.
The inclinometer takes away the possibility of this error, and so makes it the choice for me. The analog inclinometer mentioned in this thread is about $10, a cheap efficient solution.
Of course leveling the scope is another option, and actually, I do both to make things as accurate as possible.
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Rod Nabholz (Quote)
I've been told that the inclinometer reads true angle of the tube, regardless of the base angle. It certainly doesn't hurt to level the base, but I never have, & have very good results. 
Carol
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
DreamCatcher Dobservatory, #2
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Beri
sage
Reged: 06/29/05
Posts: 294
Loc: Croatia
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Quote:
I've been told that the inclinometer reads true angle of the tube, regardless of the base angle. It certainly doesn't hurt to level the base, but I never have, & have very good results.
Carol
Yes, your altitude is always correct (or to be precise, its just a small fraction of a degree off, presuming a perfect inclinometer) when the base is tilted
But azimuth is not, the error is more prominent as the tube points higher, easily 3º or even 5º depending how uneven the ground is..
To get rid of it, you need to level the base.
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15x70 Binoculars
10" truss Dob
http://www.scopemaking.net
Edited by Beri (02/19/07 04:41 PM)
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csa/montana
Den Mother
Reged: 05/14/05
Posts: 39594
Loc: montana
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Ahh, I see what you mean! Thanks for clarifying it! 
Carol
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
DreamCatcher Dobservatory, #2
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Beri
sage
Reged: 06/29/05
Posts: 294
Loc: Croatia
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Maybe this will help you understand the problem
In red, there is obvious drift in azimuth, when the base is tilted, althoug both the azimuth scale and the inclinometer show correct values. As you can see, the error in altitude is small, negligble, but azimuth is serious
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15x70 Binoculars
10" truss Dob
http://www.scopemaking.net
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Beri
sage
Reged: 06/29/05
Posts: 294
Loc: Croatia
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Quote:
Ahh, I see what you mean! Thanks for clarifying it!
Carol
Well I guess I was too slow drafting this up 
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15x70 Binoculars
10" truss Dob
http://www.scopemaking.net
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marxy
professor emeritus
Reged: 09/02/06
Posts: 629
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Hey all.
I will be picking up my 8" dob on tuesday next week, and have already prepared all I need (hopefully).
I want to know how people have attached te diital inclinometer?
I have removed mine from it's holer, but how can I attatch it to the OTA?
Thanks alot - this thread has been a great help
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Jay
All that's needed is some clear skies!
Sorry for my english, I'm learning
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 897
Loc: Iowa
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Which Inclinometer did you buy and what kind of scope, (Truss vs Tube, tube material, etc.)?
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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marxy
professor emeritus
Reged: 09/02/06
Posts: 629
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It is the lidl one from england - I can't find a webpage for it.
it isaccurate to +/- 0.3 degrees and has a metal finish to it.
It is to mounted on a skywatcher 8" - solid tube (I think it is metal)
Thanks
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Jay
All that's needed is some clear skies!
Sorry for my english, I'm learning
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csa/montana
Den Mother
Reged: 05/14/05
Posts: 39594
Loc: montana
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Marxy: Does it have a magnetic strip on the base? If not, I would glue a magnetic strip on the base, & then it will just "stick" wherever you want it on the tube.
Carol
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
DreamCatcher Dobservatory, #2
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marxy
professor emeritus
Reged: 09/02/06
Posts: 629
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csa/montana - It doesn't have anything magnetic on it (nothing a quick trip to the hardware store won't fix though), so I'll stick on a magnetic strip.
Thething is, are all OTAs magnetic?
I tried it once by puttg a fridge magnet onto my antares refractor and it didn't hold at all!
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Jay
All that's needed is some clear skies!
Sorry for my english, I'm learning
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kestrel0222
Carpal Tunnel
Reged: 05/21/06
Posts: 2338
Loc: Milford, Michigan
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My refractor is aluminum, not steel.
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Tom
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 897
Loc: Iowa
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Velcro is another option for non magnetic surfaces. The industrial strength stuff will hold it just fine.
Is there any chance magnets will interfere with the mechanism in the unit? I admit that I don't know how they work. Anybody know for sure, or anybody using magnets and getting along OK?
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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csa/montana
Den Mother
Reged: 05/14/05
Posts: 39594
Loc: montana
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If a fridge magnet won't adhere, then as Rod suggests, velcro would work fine.
You will enjoy this system so much!
Carol
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Carol
AstroTech 16" Dob (Thanks ASTRONOMICS!)
Vixen 80MF/AstroTech Voyager
Masuyama's 7.5, 15, 25W, 35mm,
Pentaxes; 5XW, 7XL, 10XW.
14mm Meade 4000 UWA
TV Panoptics; 22, 35
DreamCatcher Dobservatory, #2
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marxy
professor emeritus
Reged: 09/02/06
Posts: 629
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Won't the velcro mean that the measurer isn't aligned completely with the tube (since it sticks up slightly) and will give a sligtly 'false' reading?
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Jay
All that's needed is some clear skies!
Sorry for my english, I'm learning
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rnabholz
scholastic sledgehammer
Reged: 07/25/04
Posts: 897
Loc: Iowa
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Quote:
Won't the velcro mean that the measurer isn't aligned completely with the tube (since it sticks up slightly) and will give a sligtly 'false' reading?
If you mounted the velcro on the bottom of the level, there is some possibility you could introduce some small error. In practice, I believe it would likely be very small and could probably be avoided with careful attachment of the level to the velcro.
Another approach would be to bolt a short piece of angle aluminum directly to the tube and then place the velcro on the upright of the aluminum and the back of the level. You place the level on the base of the aluminum and slide it back into the velcro. Doing it that way you can assure that the level will match the angle of the tube.
If you want the next level of accuracy, you could take the approach that I used (as pictured above) and build a mount that allows you to adjust the level to match the readings of the computer.
You could always start the simple way - velcro to the tube- and see if you see a problem with errors. If you do, it would be easy to take it off and go to the next step.
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Rod Nabholz
Home Built Astronomy Projects
Wild Bird Photography
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