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Author Topic: spirit level - space between bubble and circle line  (Read 3030 times)
Aristoc
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« on: September 18, 2010, 09:09:39 AM »
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Hi

I was wondering if anyone knows this:

When using a spirit level, there is a small space between the bubble, and the circle. Sometimes the bubble can be a little bit closer to the circle or it can be right in the center. How much degree's difference does that little amount of space between the bubble and the circle represent from being perfectly horizontal ?

Thanks.
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Nigel Johnson
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« Reply #1 on: September 18, 2010, 09:35:04 AM »
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Aristoc

Unfortunately your question is impossible to answer as it depends upon the particular level and the curvature of the inside of the vial containing the fluid and bubble. Very accurate levels have hardly any curvature so there would be little difference, whereas less accurate ones have more curvature and would have a greater angular difference.

You can get a feel for the accuracy (and could even measure it) by taking two pictures of a scene with clear lines in it with the bubble set at either side of the circle and then comparing the images.

Regards
Nigel

Edited to add additional info.
« Last Edit: September 18, 2010, 09:42:16 AM by Nigel Johnson » Logged
Slobodan Blagojevic
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« Reply #2 on: September 18, 2010, 09:42:12 AM »
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I knew it! I knew that one day one of the last unresolved mysteries of the mankind will... bubble up. Smiley
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Slobodan

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Aristoc
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« Reply #3 on: September 18, 2010, 09:48:57 AM »
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 Wink

Good idea to take some pictures and test it out myself some time.

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pikeys
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« Reply #4 on: September 18, 2010, 12:08:30 PM »
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From what I've read,there are many levels out there..all varying in price.
The cheaper ones,actually don't work correctly ,or it is difficult in getting the bubble to accurately center.

I just ordered one from these people:
http://www.kirkphoto.com/Bubble_Level.html.

Got a good product,and service was great.
Hope this info helps,

Mike
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Aristoc
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« Reply #5 on: September 18, 2010, 03:51:39 PM »
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THat's a good price at Kirk. Thanks for the info.

I guess it's pretty similar to using a horizontal level when hanging a photo or something on the wall. As long as the bubble is between the two lines as much as possible, then you should be OK.

« Last Edit: September 18, 2010, 03:53:17 PM by Aristoc » Logged
BartvanderWolf
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« Reply #6 on: September 18, 2010, 05:43:03 PM »
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THat's a good price at Kirk. Thanks for the info.

I guess it's pretty similar to using a horizontal level when hanging a photo or something on the wall. As long as the bubble is between the two lines as much as possible, then you should be OK.

One would hope so ...

Unfortunately things are not that easy. It all depends on the accuracy of the device (vial and enclosure, even electrostatic charge can play a role) and the reference/mounting base. These 'hotshoe' mounted levels are not that accurate to begin with, and the mounting leaves a significant amount of play and thus inaccuracy.

Of course one can estimate the overall bias by checking the difference between two 180 degree opposite readings, but that doesn't solve the low repeatability of a reading.

But then, even with an accurate device and a repeatable mounting, how rotation-free is your sensor mounted?

Cheers,
Bart
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BernardLanguillier
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« Reply #7 on: September 18, 2010, 05:59:27 PM »
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Unfortunately things are not that easy. It all depends on the accuracy of the device (vial and enclosure, even electrostatic charge can play a role) and the reference/mounting base. These 'hotshoe' mounted levels are not that accurate to begin with, and the mounting leaves a significant amount of play and thus inaccuracy.

Of course one can estimate the overall bias by checking the difference between two 180 degree opposite readings, but that doesn't solve the low repeatability of a reading.

But then, even with an accurate device and a repeatable mounting, how rotation-free is your sensor mounted.

Yep, indeed. Camera based sensors are the best option.

Cheers,
Bernard
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A few images online here!
BartvanderWolf
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« Reply #8 on: September 18, 2010, 06:35:30 PM »
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Yep, indeed. Camera based sensors are the best option.

Hi Bernard,

Which BTW rules out built-in electronic acceleration sensors, their 1 degree 'accuracy' is way too low for practical use. I use a digital level with much higher (0.05 degree) accuracy, although the mounting surface and sensor rotation issue still remains.

Cheers,
Bart
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Aristoc
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« Reply #9 on: September 18, 2010, 08:47:11 PM »
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Is this the kind of digital levels you are talking about too?
http://store.tagotech.com/product_info.php?cPath=25&products_id=523&osCsid=e71b75415b3805c5f21fab2905be5bb9



or,




I guess the Canon EOS 7D had an internal one, double axis...
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BartvanderWolf
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« Reply #10 on: September 19, 2010, 05:14:49 AM »
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Is this the kind of digital levels you are talking about too?

I have no idea how accurate it is, and I also don't see it mentioned if it can be calibrated.
The one I use is the Digipas DWL-80G Pro. The Pro version has 0.05 degree accuracy.

Cheers,
Bart
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