Mount levelling and goto accuracy

[newbie alert]

Ive found if im bang on level and pa as best as i could i get a better tracking and accuracy..

I used to roughly level and then align but got too much drift..so now i level and polar align i get much better results..all unguided..my next step is guiding and sharp cap etc

[kirkster501]

15 hours ago, Filroden said:

I always thought that if the mount was not level then any adjustment you made to either alt or az during PA would introduce a small change to the opposite axis. So if not perfectly level you would have to iterate adjustments between alt and az to gradually hone in on your PA. If the mount is level, the alt and az axis are truly independent so a single adjustment to each could be possible. 

Nope.  It does not matter.  As long as the mount axis points to the NCP that is all that matters. Think about it: all that is needed is that the scope tracks about an axis parallel to the rotation of the Earth....  Whether or not your mount is "level" ( a arbitrary localized concept) just not matter a jot....

[Filroden]

7 minutes ago, kirkster501 said:

Nope.  It does not matter. 

I never said it did. What I said was having a level mount makes it easier to achieve polar alignment by ensuring the alt and az axes move independently.

As Neil also said, you can achieve PA without the mount being level. But why would you make that harder to achieve when levelling the mount is so easy and only needs doing once if you then mark the legs and the ground beneath the tripod legs. 

[kirkster501]

14 minutes ago, Filroden said:

I never said it did. What I said was having a level mount makes it easier to achieve polar alignment by ensuring the alt and az axes move independently.

As Neil also said, you can achieve PA without the mount being level. But why would you make that harder to achieve when levelling the mount is so easy and only needs doing once if you then mark the legs and the ground beneath the tripod legs. 

Agreed.  My mount *is* level, it looks daft in an observatory if it isn't level.  What I and others are saying in contributing to this discussion, is that it does not *need* to be.  Sometimes if observing on an incline it is difficult to get it level.  I've had my mount at 20 odd degrees incline before, polar aligned and it worked perfectly, albeit a little strange to get the scope and weights mounted.

[ollypenrice]

I don't think it is all that easy to level mounts! Seriously...

1) In the field you spend quite a long time tinkering with leg length to get the tripod level. The owner of a non-level-able* Tak EM200 will be fully polar aligned before the conventional mount owner has got his tripod level. That could easily be literally true. And  'Time is photons...'

2) In constructing a pier it is not easy to make a level-able top which is as stiff as a fixed top. I will never be a fan of massive piers set in sea-defences of buried concrete but ending in three or four lengths of threaded bar. It defeats the object for no purpose.

I don't suggest wantonly making a pier with a top at a jaunty angle, but I would rather have a rigid, non-adjustable pier with a roughly level top than have a compromised one I could adjust. If the argument flies off into theoretical fantasy and has us imaging alpine-sloping tops then we all know the facts. You can still polar align and you will have serious axis-interaction when drift aligning. In a more practical conversation about whether or not to make pier tops capable of fine tuning, I would say don't. There is no point and the axis interaction is trivial.

Olly

* A hyphen too far, methinks... 

[Davey-T]

When I've made piers I've always incorporated some way of leveling the top, but not on long spindly bolts, I've also made sure the pier was upright and the square parts [were] square with nice smooth edges and finish.

Having gone to all this trouble it seems churlish not to have the mount more or less level if only for ascetic reasons, possibly just a bit OCD but it's just as easy to have it level.

I think the big lump of concrete tradition originated on CN and was more about combating the extreme climatic conditions suffered by our American cousins than preventing normal temporary movement, whatever that is, maybe a train or truck passing by or the observer stamping their feet to warm them up.

One other thought, when using my iEQ45 for solar imaging I set it up on premarked spots and LEVEL it and then GoTo and track the Sun so no Polar alignmemt being daylight 

Dave

[ollypenrice]

I don't think that anyone looking at the kind of tilt I'm talking about would be able to see it without a spirit level.

Olly

[Stub Mandrel]

This debate exactly parallels a regular discussion on 'levelling a lathe'. It matter not one jot whether or not the bed of lathe is level and the best test of lathe alignment is whether or not it will turn a parallel cylinder, not whether or not the two ends of the bed are perfect level and aligned. This still does not stop people paying huge sums for super precise spirit levels (accuracy measured in arc-minutes) rather than simply turning a test piece and adjusting until it is error free. Nor does it stop lathes working accurately on board a ship...

l

[ollypenrice]

2 hours ago, Stub Mandrel said:

This debate exactly parallels a regular discussion on 'levelling a lathe'. It matter not one jot whether or not the bed of lathe is level and the best test of lathe alignment is whether or not it will turn a parallel cylinder, not whether or not the two ends of the bed are perfect level and aligned. This still does not stop people paying huge sums for super precise spirit levels (accuracy measured in arc-minutes) rather than simply turning a test piece and adjusting until it is error free. Nor does it stop lathes working accurately on board a ship...

l

...although GEMs will not work accurately on ships!  (Hey, I'm a gienius...)

Olly

Edit: sometimes I can even spell genius...

[1parsec]

Here's my example of a telescope perfectly polar aligned and with the base not level !!  The base or tripod definitely does not need to be level to get perfect polar alignment ;-)

As a couple of people mentioned, there was is interaction between Alt and Az adjustments when polar aligning when the base isn't level, but getting a good PA was still quite quick and easy.

I made the pier and didn't feel the need to spend another £500 on a wedge.  This was my set up about 17 years ago and now long gone.

 

[spillage]

@1parsec but how can we be sure the obs is not on a slope?? Do you have a photo with a level shown in it...just to be sure. 

[ollypenrice]

16 hours ago, 1parsec said:

Here's my example of a telescope perfectly polar aligned and with the base not level !!  The base or tripod definitely does not need to be level to get perfect polar alignment ;-)

As a couple of people mentioned, there was is interaction between Alt and Az adjustments when polar aligning when the base isn't level, but getting a good PA was still quite quick and easy.

I made the pier and didn't feel the need to spend another £500 on a wedge.  This was my set up about 17 years ago and now long gone.

 

Ah, but nobody doubts the need to put a fork mount on a tilt (unless at the equator or one of the poles!) The controversy surrounds the bases of GEMs. You had a good system there with simple but nifty fine tuning.

Olly

[Zakalwe]

A picture tells a thousand words. Even a finger painting by an idiot (me) in Photoshop

Each telescope has had their respective mount top levelled. The ones at the pole and equator are at right-angles to each other. The one at 45 degree latitude is between these two extremes. The only common thing is that all telescopes are polar aligned, so their Right Ascension axes are all parallel and are pointing at the NCP.

Remind me again why levelling a tripod is necessary?

 

Levelling a tripod ONLY places it tangentially to the surface Earth, which itself is tilted at an angle. The only thing that is necessary is to have the RA axis pointing at the celestial pole. Everything else is irrelevant.

 

 

[Paul M]

I spent most of my working life caring about and worrying about stuff being level. I've no patience for it in my leisure time!

My EQ6 gets plonked on the grass with a rough visual alignment to the north. I can do this in daylight and be near enough. When Polaris comes into view as the sky darkens I squiggle the knobs to get Polaris anywhere inside the polar scopes PA circle. I don't give even a seconds thought to PA. 

Then 2 or 3 star alignment and I'm away. I don't do imaging so all that matters is that GOTO's deliver my target and they very rarely fail.

Horses for courses

[spillage]

I have just purchased this 

 

Dewalt Dw079pkh Self Levelling Rota..pdf

 

Will this help?

[1parsec]

3 hours ago, ollypenrice said:

Ah, but nobody doubts the need to put a fork mount on a tilt (unless at the equator or one of the poles!) The controversy surrounds the bases of GEMs. You had a good system there with simple but nifty fine tuning.

Olly

I should have made my point clearer and that was the alt-az adjustments do not need to be level to the ground like an EQ mount doesn't :-)  

 

[1parsec]

5 hours ago, spillage said:

@1parsec but how can we be sure the obs is not on a slope?? Do you have a photo with a level shown in it...just to be sure. 

I was standing upright. Honest ;-)

 

[iapa]

6 hours ago, spillage said:

I have just purchased this 

 

Dewalt Dw079pkh Self Levelling Rota..pdf

 

Will this help?

mmm

Probably not - 1mm/m is way too inaccurate for our purposes

LOL

[Geoff Lister]

Both of the alt-az mounts on my Skywatcher Skymax 127 MCT, and Skyliner 250 Dob, have nice alt scales and a moving pointer by the OTA's clamp. By starting with a level mount, I can speed up alignment when the handset asks "slew to xxx yyy", I can set the alt on the scale and use a compass to get the az close enough for the finder scope.

The little bubble level on the tripod is reasonably accurate, when checked with a spirit level, and I have added a larger bubble level to my Dob turntable.

[ollypenrice]

On 03/03/2017 at 15:08, Zakalwe said:

A picture tells a thousand words. Even a finger painting by an idiot (me) in Photoshop

Each telescope has had their respective mount top levelled. The ones at the pole and equator are at right-angles to each other. The one at 45 degree latitude is between these two extremes. The only common thing is that all telescopes are polar aligned, so their Right Ascension axes are all parallel and are pointing at the NCP.

Remind me again why levelling a tripod is necessary?

 

Levelling a tripod ONLY places it tangentially to the surface Earth, which itself is tilted at an angle. The only thing that is necessary is to have the RA axis pointing at the celestial pole. Everything else is irrelevant.

 

 

No, but you see I like the base of my EQ mount to be parallel with my bird table. This has nothing to do with astronomy but that's how I like it to be. You see my bird table is orientated NNE and at 12 degrees from the horizontal. It always has been, and the birds like it that way.

lly

[Stub Mandrel]

9 minutes ago, ollypenrice said:

No, but you see I like the base of my EQ mount to be parallel with my bird table. This has nothing to do with astronomy but that's how I like it to be. You see my bird table is orientated NNE and at 12 degrees from the horizontal. It always has been, and the birds like it that way.

lly

Bird tables or not, I still think the simple answer is 'how do you think they polar align the Hubble Space Telescope?'

[Gazabone]

Personally I always level the mount, not so much from a pointing accuracy perspective, more for safety. A friend of mine put up a heavy refractor on an EQ5 (not goto) at a public event. I ended up aiming it at something someone requested and because it was on a bit of a slope, the whole thing toppled on top of me. Fortunately neither the scope or me came to any harm but a salutary lesson nevertheless. 

[newbie alert]

1 hour ago, Stub Mandrel said:

Bird tables or not, I still think the simple answer is 'how do you think they polar align the Hubble Space Telescope?'

No earths axis to worry hubble

[Stub Mandrel]

8 hours ago, newbie alert said:

No earths axis to worry hubble

Exactly, the earth is purely incidental to the alignment of our telescopes, it's just a convenient surface to place it on - with the inconvenient habit of rotating.

[Zakalwe]

11 hours ago, ollypenrice said:

No, but you see I like the base of my EQ mount to be parallel with my bird table. This has nothing to do with astronomy but that's how I like it to be. You see my bird table is orientated NNE and at 12 degrees from the horizontal. It always has been, and the birds like it that way.

lly

 

Dammit man....we need more information!  How many tonnes of concrete are under the bird table?