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Old 23-07-2018, 05:08 PM
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darrellx (Darrell)
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Lets Talk "Levelling"

Hi All

I have been reading a bit about levelling a mount and I would like to clarify whats acceptable or okay. I read where some say near enough is good enough.

First of all I realise that it depends on the use - visual or photography. So lets say this is for photography. Also, lets say this is for levelling either a pier base or a tripod, and the distance across the base plate is 200mm.

I have attached three pics from a "simulation".

In my mind, pic 1 shows perfect levelling. The bubble is nicely centred between the lines. This would be the ideal.

Pic 2. The bubble is still between the lines, but is off-centre.

Pic 3. The bubble is outside the lines, or part of it is.

The question is, would pic 2 represent an acceptable (workable?) or okay levelling of the mount for photographic purposes? Across a 200mm mounting plate, this represents a variation of about 1mm.

Pic 3, I think would be unacceptable or not okay for photography but may be okay for visual.

From what I have been reading, if I interpret correctly, guiding can overcome some problems if the mount is not perfectly levelled.

I am interested to hear opinions.

Thanks
darrell
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  #2  
Old 23-07-2018, 05:33 PM
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OzEclipse (Joe Cali)
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Permanent pier - doesn't matter. It might take you a bit longer to get it aligned but once aligned, the base can be at 45 degrees to level, the mount, goto system won't know the difference.

Portable - when the base is not level, a movement in ALT, changes AZ and a movement in AZ changes ALT. When you get close to the pole, and providing the base is not way out of level (eg 45 degrees) these changes become very small.

Can't interpret the angles from the bubble pics, different levels show different bubble displacements at the same angles.

In short it doesn't matter for either and levelling doesn't have to be perfect for an EQ mount.
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Old 23-07-2018, 06:00 PM
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barx1963 (Malcolm)
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I like to get my mount reasonably level. Mainly focus on east-west tilt accurate as the north-south tilt will be corrected when I do polar align anyway. Main reason for being a bit more finicky with the EW tilt is that the RA home position is going to be affected if it is out which will throw any go tos out.
Of course if you are talking a permanent setup, it really is not important, polar alignment will take care of any issues.

Others with more knowledge may entirely contradict what I have just said, but works for me!!

Cheers

Malcolm
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Old 23-07-2018, 06:48 PM
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The_bluester (Paul)
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IMO levelling is not that important on a GEM, particularly if you will do some form of drift alignment. If the RA axis is parallel to the axis of the earth, who cares what angle the pier plate is on. It just might take more work to get it aligned right depending on the error and might mean adjusting one axis puts the other out of whack.


In the case of a goto Alt Az it is IMO more important. One of the assumptions in the software is that the azimuth axis is properly plumb. You might claw some accuracy back with a three star alignment and/or re centering objects in the software but IMO it is just kludging a software fix for a physical setup issue and some other error is bound to squirt out of a gap somewhere. If that error is noticeable is a different story.
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Old 23-07-2018, 06:56 PM
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iborg (Philip)
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Hi


I agree about pic 1, but, I can be a suspicious bugger, I normally also reverse the level to confirm bubble position.


As for how critical is, I don't really know.


Philip
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Old 23-07-2018, 07:45 PM
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doppler (Rick)
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I prefer to use a "bulls eye" level.
https://www.bunnings.com.au/empire-b...level_p5660623
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Old 23-07-2018, 08:01 PM
Wavytone
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Hi Darrell, I have an AZEQ6 which I use both altaz and equatorially.

In EQ mode it isn't really necessary to level the tripod, but levelling it first means minumal futzing - often none - with the altitude setting assuming it was set up that way last time.

In altaz mode levelling the tripod N-S and E-W is essential, it makes a HUGE difference to the accuracy of the subsequent alignment and subsequent GOTOs if this is done to 0.1 degree, and for this I use an iPhone app "clinometer" (ie a big bubble level) which I calibrate beforehand.

With a smaller scope it might not be so critical but at a focal length of 3100 the field of view of my beastie is a tad over 0.5 degree. With care the mount will put the scope regularly within 15 arc minutes of the target, without doing anything special beyond a basic alignment.

The Synscan handset can also do localised corrections for up to 85 patches of sky by I haven't explored that feature yet.
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Old 23-07-2018, 08:26 PM
DJT (David)
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Hi Darrell

If this is for your APMach1, suggest you use the bullseye level embedded into the mount! Slightly different viewpoint.


If you are in the field, getting the mount level is a pre-req in the user manual so that you can use the daytime polar alignment routine quicklywhich will get you close enough for guided imaging.

Given that they provide you with a bullseye level built in, its only the work of a minute to get it close enough.


D
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Old 23-07-2018, 08:29 PM
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leon
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It is not that important if the mount is permanently mounted on a pier, and as mentioned once properly aligned it will function fine.
I do have to admit I also liked mine to be perfect, but at the end of the the day it was of no consequence

Leon

Leon
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Old 24-07-2018, 07:03 AM
issdaol (Phil)
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For every AltAz GoTo Mount that I have owned, correctness of level has made a huge difference on accuracy of GOTO’s

In every other circumstance...if you are setting up an EQ permanently or in the field why would anyone do a half assed job and not level perfectly ???

From a practical sense it only takes a very small amount of extra effort over a “close enough” level anyway so why skimp.
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Old 24-07-2018, 08:09 AM
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darrellx (Darrell)
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Thanks for the responses. Yes, this is in relation to my Mach 1.

I have three places that I will setup. One at home, one at my dark site, one on a tripod at a friends place.

At my dark site, I spent a LOT of time making sure the pier was very level. Thats Pic1.

At home, I haven't worried too much about it. I don't expect to use it a lot at home. I really did it for testing purposes. Thats Pic2.

The tripod is the question. In the past with my EQ6 I felt I was chasing my tail a bit, and would eventually say "ah, what the hell". When in this situation I did the same - focus on the east/west level more than the north/south level and it did seem to work well.

But being an eq mount, and I usually guide, it sounds like the levelling in Pics1 and 2 will be fine. When I get setup, I will take some pics of the bullseye level. I didn't realise you could get them at Bunnings.

Darrell
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  #12  
Old 24-07-2018, 08:19 AM
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Marke (Mark)
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The Mach1 has a lvl built in you just use that and as others have said its not important to be dead lvl if polar aligning.
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