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#1 Bart

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Posted 05 May 2011 - 12:58 PM

When everything else is considered, how important is it for the tripod to be absolutely level? If the bubble in within the circle is that good enough? For example, a CGEM tripod.

#2 jmiele

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Posted 05 May 2011 - 01:14 PM

Night to night keeping level mean less gross adjustments in Alt. Some systems do require a level setup to function better. To me, only level N-S is required. E-W means nothing as is only affects R/A and NOT Az adjustment. Joe

#3 Bart

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Posted 05 May 2011 - 01:25 PM

Let me put it another way. Should I trust the tripods bubble level?

#4 Phil Sherman

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Posted 05 May 2011 - 01:31 PM

Assume your tripod was perfectly level and your home position was perfect last time you set up your mount. If the tripod is one degree off (E-W) tonight and you use your setting circles to locate the exact same home position; your RA axis will be off by one degree, or about two moon widths.

You can correct for this by adjusting the home position to account for the tripod's tilt. Once you complete a multiple star alignment; the mount's software should compensate for any errors in leveling or the home position.

Phil

#5 mak7

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Posted 05 May 2011 - 01:38 PM

Not really, my built in bubble does not show the same result as a 1.25" bubble placed on the tripod top of my CGEM. I have an extension mounted to the tripod and place a 1/4" x 3" aluminum bar over the extension, then place the bubble on the bar. This, of course, before I put the mount head on the extension.

The small built in bubble is usually far off in alignment.

YBIB may vary. ( Your Built In Bubble )
Brad

#6 clchildress

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Posted 05 May 2011 - 01:45 PM

The built in bubble level on my CGEM is pretty sub-par. I bought a cheap hardware store bubble level and use that instead.

#7 Skylook123

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Posted 05 May 2011 - 01:51 PM

I've had several mounts where the bubble level was way off. But my current Atlas mount bubble is dead on in agreement with a bulls-eye level used on the tripod prior to installing the mount head. Just lucky; most Atlas EQ-G/Synta EQ6 folks say theirs is just as inaccurate as any other.

My latitude indicator on the mount head is awful; about four degrees out.

#8 skybsd

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Posted 05 May 2011 - 02:41 PM

Hello,

Let me put it another way. Should I trust the tripods bubble level?


Most folks tend to find the built in or included bubble levels to be less than accurate.., If you can, you'd want at least get a decent multi-plane spirit level from your local hardware store - works quite well.

Regards,

skybsd

#9 Eddgie

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Posted 05 May 2011 - 02:56 PM

No, not necessary at all.

If you are doing visual only, the electronics will calculate the error for you.

If you are imageing, you will need to do an accurate polar alignment. In this case, leveling is nice, but not necessarly essential. Most people use Drift Alignment to do a final touch up of the alignment and it might take a bit longer if the tripod is not PERFECTLY level, but getting an tripod PERFECTLY level is in itself a bit tedious sometimes.

So, for visual, just put the bubble in the circle and call it good.

Regards.

#10 skybsd

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Posted 05 May 2011 - 03:13 PM

Actually - I'm a visual-only observer and do make sure to level my field tripods, and do not find it tedious at all :)

Regards,

skybsd

#11 ADBjester

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Posted 05 May 2011 - 04:04 PM

Let me put it another way. Should I trust the tripods bubble level?


No. I find my CGEM mount's bubble is inaccurate compared to a true carpenter's level, which I carry in my kit. If I'm carpenter-level N/S and E/W, my bubble is *well* off center, with only about a third of the bubble inside the circle.

I don't eyeball it. I level it the old-fashioned way.

Jester

#12 Bart

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Posted 05 May 2011 - 04:26 PM

I can get the tripod level when the mount is not on. But, the legs aren't fully extended until leg brace is tightened. That can only happen when the mount is screwed onto the tripod. When the brace is then tightened the legs are not extended evenly due to the brace not contacting the legs evenly. And there goes the perfect level.....

#13 WadeH237

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Posted 05 May 2011 - 06:07 PM

For an equatorial mount to track well, the only thing that matters is polar alignment. For deep sky goto, the only thing that matters is correct alignment stars (and something to account for orthogonality, which on the CGEM, means the calibration stars.) For goto of planets, the moon, etc., the deep sky alignment and correct time matter.

None of this is affected by whether the tripod is level or not. That said, there are some reasons why you do want the tripod to be level. One of these reasons is that the mount assumes that the tripod is level in the context of not crashing the telescope into the tripod. Another reason is that, when you do the polar alignment, it's easier to make the physical adjustments if the mount is level.

The three key takeaways from all of this is this:

1) Don't sweat getting the tripod perfectly level. Close is good enough.

2) If you are doing visual only and don't have the strict tracking demands of astrophotography, close is also good enough on the polar alignment.

3) If you want really good goto performance, spend your setup time getting the alignment and calibration stars right. Either use a reticule eyepiece or defocus the scope so that the alignment star is a big donut (it's easier to center accurately.) Also, for a CG5/CGEM/CGE/CGEPro, always approach your alignment stars so that up and right are the last two buttons that you press when centering a star. This ensures that the gears are always loaded the same way that the scope does its goto approach and removes backlash as a source of alignment error.

I hope that this helps,
-Wade

#14 jmiele

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Posted 05 May 2011 - 06:47 PM

The point I was making is that if you level every night less adjustment will be required in Alt. Is it required...NO N-S out of level is made up by Atl adjustment. E-W out of level is made up via R/A. As for the bubble level, it is a reference. If at home in the same basic location each night you put the bubble in the same spot - it WILL have the desired affect even if it (the bubble level) is not 100% accurate. Because it's ONLY a reference.

Joe

#15 Eddgie

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Posted 05 May 2011 - 08:57 PM

This is the way I use the bubble level in my scopes for visual work.

It doesn't matter to me if the mount is perfectly level.

I just put the bubble in the circle. I don't really care if the level on the mount is innacurate because like you, I only use it as a reference to get a repeatable mount setup.

I never have to move the mount in Altitude. Only Azimuth.

And if it is off a bit, I don't really mind.

Even in my C14, I find this method sufficient to get a good initial alignment and repeatedly accurate Go-Tos.

As much power as I use in the C14, the small amount of drift that I get by not being perfectly aligned is pretty negligable, and easily dealt with with an occasional bump of the Dec button on the handset, but this is rare for me to have to do this. ONly when powers are above 300x or so.

For the EdgeHD on the CG5 ASGT, I do the same thing. I just use the bubble as a referecnce so that the scope is always set up the same (and I have the altitude adjusted properly for the bubble LEVEL, Not FOR LEVEL-level). In the smaller scope, drift is never a problem.

So, like you, I just use the bubble as a reference so that the altitude is right, and whatever error existe in the E/W level of the instrument doesn't bother me.

#16 jmiele

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Posted 05 May 2011 - 10:50 PM

Agreed Eddgie. Lately I have been doing my polar alignment on the 900 via the polar scope, going to a bright star, releasing the clutches and centering. That's it. Perfect all night. Joe






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