EQ6 bubble level

[matt]

Just out of curiosity...

how reliable are those bubble levels built into the mount head of the EQ6?

I'm guessing about as accurate as the latitude scale on the side of the mount... as in, not very accurate at all?

I just checked the tripod without the mount on it (from last night when the mount bubble had been "levelled") and it was wayyyyyyy off!!!

OOOps... this should be in the equipment forum (mods)

[h0ughy]

your guess is as good as mine. I have one old Eq6 without one and one with one. the one with it, if I level the tripod with a spirit level, and then put it on it, I still need to adjust the level? SO I am beginning to wonder?

[matt]

Houghy. My suspicion is the bubble level isn't reliable.

I used a very good spirit level today on the tripod alone and got it level in all directions.

Popped the mount on and the small built-in level said i was a mile off.

Don't know whether it's something to do with the maching of the mount-tripod interface or what?

The prob is there's just no way to check everything's level once the mount is on the tripod. You can only go off the built-in bubble

[ballaratdragons]

Geez, how can they get something as simple as a bubble level wrong??? :screwy:

Maybe it's a Northern Hemisphere bubble and it wants to go to the bottom instead of the top :lol:

Makes you wonder about QC!

[matt]

Weird, huh Ken? You'd think all bubble levels would perform the same?

After all, they're just a bubble suspended in liquid!

But it does seem some are more accurate than others for whatever reason.

I wonder whether the "tradies" among us could shed some light on the varying accuracies of bubble/spirit levels?????

[ving]

yup, weird alright :)

[Astroman]

I havent used the bubble level on the mount, best way is to use a small spirit level on the tripod prior to puttting the head on, but if the ground is soft it may move. maybe a small sheet of aluminium that extends beyond the tripod base diameter so a small level can be sat on it. My bubble level seems okay for visual use but for more accuracy I think using a different method is needed.

[matt]

Nah. Tripod is set on concrete.

Will see how it goes levelling with spirit level rather than mount bubble level

[Doug]

For an EQ mount it probably doesn't matter all that much. Once the polar axis is aligned, that is that. If the mount is being used portable, then using the bubble level should allow faster alignment with each set up whereas leveling the tripod would not necessarily be as good. leveling with an altaz is different, but the EQ is more concerned with the polar shaft being parralell with the Earth's axis.
just my thoughts
cheers,
Doug

[matt]

Why's that Doug?

Thanks

[Lee]

Doesn't the bubble level just allow you to level the tripod (in theory).... the bubble levels on my G-11 are way off also.... I just use a small Stabila level to level up the tripod instead of the integral ones.

[matt]

Lee. You'd think so, wouldn't you?

But what many of us are finding is we get a very different "level" when we level the tripod first before the mount goes on.

I level the tripod first with a builder's spirit level (before the mount goes on)

Then once the mount is on, I look at the built-in bubble level on the EQ6 and it reckons the tripod's not level:shrug:

Which do you believe?

[astro_nutt]

I don't know if this'll help...
When setting up the Dob and using the Eastro sky navigator....I first set the optical tube to horizontal at 0 degrees...rest my spirit level on the tube and adjust the height accordingly..rotate the base 90 degrees and do the same.
I found out from previous experience that there may be a varience between the base/mount and the optical components..from then on I check the level from the optics!
As for those bubble levels..some are the self-adhesive type using double-sided foam mounting tape about 1 to .5 mm thick.
I would remove the mounting tape and just stick it on with a dab of contact adhesive!
Cheers!

[Lee]

Depending what you are laying the spirit level across for one - if this is OK, then I'd trust a decent quality spirit level over the bubble level on the mount - the bubble is only as good as how it is mounted to the mount I think, if its crooked in the mount then you won't level properly with it....

[matt]

Thanks guys.

Lee - I reckon you're right. I don't think the level's been set right into its recess in the mount, hence its lack of accuracy.

Like I said, why would we expect the bubble level to be accurate when the lat scales are also hopeless?:lol:

My latitude scale is out by about 6 degrees:scared:

[Doug]

G'day Mat,
Sorry for the delay, I'm not getting email notifications through at the moment.
You ask "why's that Doug?"
What I had in mind was that assuming the mount and scope are set up initially on a concrete base, and polar aligned. Setting up again out on a field trip where the ground might not be a unyielding as concrete, leveling an unloaded tripod might not be as static as one would want. With the weight of the mount head and scope etc on the tripod one leg could settle more than the others. Leveling using the bubble should always get your polar axis fairly close, leaving only azimuth to need correcting when doing a quick drift align.
I know the bubble is not repeatably accurate for setup after setup however most people don't want to spend all night drift aligning.
hope that clears that up:)

Someone raised the point that the bubble might not be set in the mount correctly, and that is probably true. I had a quick 5min look at an EQ6 at Bintel recently (I'm obviously now a world expert):D Is that bubble cemented in or might it be easily reset?

Cheers,
Doug

[sejanus]

I'm chipping in to say my eq6 bubble is a bit weird as well. I use a seperate spirit level. my latitude scale is also miles off, despite the protests of the guys who made the mount over email that I must be wrong!

[Astroman]

I think these bits are there to get us in the ball park, most people who are serious enough would check their equipment without these aids. Doing drift alignments, checking with levels etc...

Interesting topic none the less..

how many other types of mounts show small inaccuracies like this?

[matt]

No doubt you make some valid points Andrew.

It's valuable, though, that people point out these small deficiencies for the benefit of others who have yet to discover these little "failings".

I've lost count how many times I've been slightly off in my calculations and what I've been trying to do because my gear isn't quite accurate.

It's also easily fixed, of course. It's just good to be able to let others know of potential pitfalls and what to be on the lookout for

:)

[Dennis]

Just to continue with Doug’s original comment, a mount need not be level to polar align it. At home, my Tak EM200 mount is not level and I don’t bother levelling the mount at astro camps that I attend. My Tak wooden tripod has fixed length legs and I don’t bother sliding blocks under the legs to make the mount level.

If you drift align your mount, something I have never done, having the mount levelled is a big advantage. Basically it allows you to make simple altitude and azimuth adjustments to adjust the pointing of the mount to establish an accurate polar alignment. If the mount is not level, you will have to make compound changes to Alt-Az when drift aligning.

Cheers

Dennis

[DaveO]

This thread has been very interesting! At least I know I am not alone!

At last Astrofest I struggled with my brand new EQ6's GOTO functionality. It wasn't until some week's later that I discovered that the latitude scale was off by 6-8 degrees. That had been the one thing I figured I didn't have to worry about! :sadeyes:

Now there are questions about the bubble level? :shrug:

I don't know about you, but when I pay a considerable sum of money for a mount, I expect that at least the simplest parts of it should work as advertised. After all, how hard is it to get the latitude scale aligned correctly, or to place a bubble level accurately? It wouldn't cost that much more - the time difference is not that significant and the wages aren't that high!

I really like my mount and have generaly been very happy with its performance, but these little niggles just make it harder.

Well I'm off to get a level to check the level now. :screwy:

[matt]

Hi Dennis

By this do you mean one would have to go from one to the other making (hopefully) ever-decreasing fine adjustments until the polar alignment is spot on?

Cheers:thumbsup:

[Lee]

You would think wouldn't you. Although I am becoming more of a cynic by the day when it comes to advertised vs delivered service.

[Dennis]

Hi Matt

I have never drift aligned, so what follows are my theoretical musings on the topic from trying to grapple with it in a mental model – the Tak has an excellent Polar Alignment ‘Scope. ;)

If we start out with our mount level, then our polar axis may be misaligned in altitude, azimuth or both.

An Altitude misalignment is when the mount’s polar axis is off in altitude, pointing either N or S of the true pole. With the mount misaligned in altitude relative to SCP:
Polar Axis too high? Star drifts South.
Polar Axis too low? Star drifts North.
In this case, the star is a bright star in the East, about 15 degrees above the Horizon, near the Celestial Equator.

An Azimuth misalignment is when the mount’s polar axis is off in azimuth, pointing either E or W of the true pole. With the mount misaligned in Azimuth relative to SCP:
Polar Axis too far East? Star drifts North.
Polar Axis too far West? Star drifts South.
In this case, the star is a bright star near the intersection of the Meridian and the Celestial Equator.

With drift alignment, I believe you never compensate for drift in RA, you only watch out for movements in DEC.

If the mount is not level, when you make an adjustment in say Altitude, you will also be making an adjustment in the Azimuth axis as well, so I presume the overall task becomes more difficult, possibly requiring more iterations?

Hope that helps

Cheers

Dennis

[matt]

Cheers Dennis

Believe it or not, I have already mastered drift aligning. It's one of the few things I actually know how to do!

I take it I'm correct in what I said in my prior post?

[Dennis]

From reading stuff about drift alignment, you will end up making smaller and smaller adjustments as you get closer and closer to the SCP, so yes what you said appears correct. I think you also need to watch the relevant star for longer periods to detect the increasingly small misalignment due to making the adjustments?

If your mount is level, then your azimuth movements will be parallel to your local horizon and your altitude movements will be parallel to your local meridian. Making an adjustment in Azimuth to move the mount E or W will not cause any movement in Altitude N or S and making an adjustment in Altitude to move the mount N or S will not cause any movement in Azimuth E or W.

However, if your mount is not level, then when you make an adjustment in Azimuth, you will also be making a corresponding small adjustment in Altitude as well and it is this compound motion in both axes that you want to avoid.

Hmm, must try this one evening to check how accurate the Tak polar alignment ‘scope is.

Cheers

Dennis

[Doug]

Dennis, there remains the very real possibility that the axis about which the altitude adjustment rotates might not be exactly parallel to the base of the mount/tripod base. General machining errors, flexure under load, overall lack of rigidity could easily undo the most exacting tripod leveling. I know a GE mount is not the same nightmare as a Meade super wedge aligning a fork mounted scope, however a lower budget mount is not going to be as well engineered as the more high end mounts.
cheers,
Doug