Fitting a level Bubble

[valleyman]

I am thinking of fitting a level bubble to my Dob.

I seem to remember from my army days leveling a bubble was fairly easy.

Can somebody correct me if i am wrong.

1. Fit the bubble to the mount

2. Level the bubble using the modded feet

3. turn through 180 degrees and check level

4. If the bublle has moved, remove half the error with the mount and the other half by adjusting the bubble.

5. Turn the mount 180 degrees and recheck level.

6. keep repeating 2-5 until bubble stays central.

[ollypenrice]

Couldn't you just buy one opf those double bubble devices with two little spirit levels at right angles to each other? Then you would do the whole operation in one. Builders' suppliers have them as do caravan outlets.

Olly

[yesyes]

how about something like this?

TRIPLE 3 AXIS BUBBLE SPIRIT LEVEL ON CAMERA HOT SHOE 3D on eBay (end time 30-Dec-10 08:22:40 GMT)

[derherr65]

They make a simple round bubble level that would work well. You would still like to rotate the dob to cancel out any error with any of the above levels, I would think.

[valleyman]

I have fitted a T Bubble bought from B&Q, but what I need to do is to ensure it is being mounted level on the mount.

[opticalpath]

If I understand Valleyman's question right, it's not about levelling in 2 or 3 dimenions/ axes .... but rather the procedure to detect and correct any small error in the levelling device. If there is a small error in the bubble level, then it will never read dead level in two positions on a surface if reversed back and forth through 180 degrees. So, to get the surface level, adjust for half the error indicated, reverse the level and measure again and repeat ...just as Valleyman described. Dead level will be when any small out-of-level amount showing on the bubble is equal and opposite in the two positions.

Adrian

[LukeSkywatcher]

My bubble has a black circle on the glass to show me when it is level or not.

Sorry the bubble i have is on my Horizon 8115 tripod and i think it has fallen off.

[valleyman]

Your correct Adrian. if the bubble is not fitted level to the Mount it will never be correctly leveled and |I was asking about how to correctly level the bubble to the mount.

[opticalpath]

Ah, I see Pat, you have to level the mount, calibrate the bubble-level(!), then fix it place. What I described was just the usual procedure when using a spirit level - to try it both ways round in order to minimise the effect of calibration error in the spirit level. But the principle is the same, and the procedure you described for calibrating and mounting the bubble looks right to me.

Adrian

[yesyes]

I see... sorry, I misunderstood the question then... ;-)

[yeti monster]

Is there any real need for a bubble level on a Dobsonian mount? Provided the base is standing firmly, then you only have to move the scope in Alt/Az motion to aim it at you target. The mount being perfectly level will make no difference, shirley?

[valleyman]

My back garden has a 5 degree slope So I would like to have the dob level as i will also use it for short exposure imaging

[yeti monster]

Is it one of the new fangled motorised 'Dobs' then? In which case I'd understand your problem. I always think of a Dob as being in the same vein as Mr. Dobson created, a push to alt/az mount relying on a delicate equation of balance and friction.

Good luck with the imaging. This is one reason why I'm hoisting my 10" SNT onto a motorised mount, although I'll be retaining the Dob capabilities for visual work.

[sbooder]

If a circular bubble level is cantered by adjusting the legs of your tripod or the feet of a pedestal, and you get error when turning the mount head, it is the bubble that is not correctly level within the mount and not the mount that is the problem and you will never get the mount level until you get the bubble level levelled in the mount.

I have an external bubble level that I place on the flat of the mount as I have never trusted that the inbuilt bubble level is correct in the mount.

[valleyman]

Having done the adjustment as I described in my first post can now say that the bubble is now level to the mount, as the bublle now stays central in both plains through 360 degrees.............. thanks for all the imput .