Leveling a Pier: who's right ?

[saac]

3 hours ago, Mr Spock said:

II suspect the 'doesn't need to be level' mostly comes from people who use a program to track in both RA and Dec. In which case 'level' doesn't really matter.

Nope,  it mostly comes from not being required for a GEM mount!

Jim 

Edited June 21 by saac

[ollypenrice]

On 20/06/2024 at 18:01, Swoop1 said:

I get it that a pier does not have to be perfectly level on the vertical and horizontal planes but, what about the mount that is affixed to the pier?

Should the base of the mount be level?

I ask this because, to my not too robust intellect, a mount that is not level will cause issues won't it?

You spend time reaching perfect polar alignment but, when the mount is directed to aim the OTA at a particular celestial target, the non level mount will cause tracking issues wont it?

Shirely tracking accuracy will depend massiveley on a level platform to work from?

Signed Swoop1 D&C (Dazed and Confused)

No.

This is really very easy if you try a thought experiment...

Spend 3 hours leveling the top of your pier to perfection. Polar align your mount to perfection. Now pass a snug fitting steel shaft through the polar axis of your mount and weld it to brackets fixed on the floor and wall. Your polar axis (polar alignment) is now absolutely fixed and cannot go wrong. Agreed?

Now unbolt your pier from the ground and loosen your mount's altitude and azimuth adjusters. Your polar alignment cannot change because of that steel shaft through the polar axis - but you can now point your pier where the hell you like and doing so has no effect whatever on your polar alignment.

On 21/06/2024 at 19:58, Mr Spock said:

Tracking with a 'level' EQ5 

This is with a Nikon D500 and StellaLyra 6" CC at 1836mm. Image purpose is to determine field scale and magnitude limit for future variable star estimates. It isn't meant to be aesthetically pleasing. Image is of ε Boö.

Not bad tracking I would say  Scope looks good too!

 

Tracking looks fine but this has absolutely nothing to do with where your pier or tripod was pointing. See above. My watch keeps excellent time and has a black face. This does not mean that only watches with black faces keep excellent time. You mention programs which track in RA and Dec but these don't exist, unless you mean encoder-guided mounts. Unguided mounts can only track in RA. Where would they get information about accumulating errors in Dec? Guided mounts get this information from the guide star position and encoder-guided mounts get it from the encoders which have been calibrated against a sky model.

On 21/06/2024 at 18:58, saac said:

If not level it will impair pointing accuracy and repeatability I think for the particular sky model. It will certainly do so when using manual setting circles. 

Jim 

Using a fixed sky model on a mount which which was assembled and disassembled would be very optimistic and I don't think anybody does that, do they? High grade, fixed observatory mounts with absolute encoders bolted to 6 tonne concrete bases need their sky models renewing maybe 2 or 3 times a year. I host a couple of these. Similarly, re-using an alt-az sky model after moving a mount really ain't going to work.

If you get a good polar alignment (which has nothing to do with level piers) you really only need a one star alignment for a perfect sky model, but a perfect polar alignment is difficult so a 3 star alignment will give one with built in PA error (and cone error) correction. The sky model is made from the position of the star relative to the polar axis, not relative to the top of the pier - about which the software knows nothing.

If a level pier top is needed, please explain how the Mesu seen earlier in the thread, with its pier top tilted to the equatorial angle, can give a periodic error around ten times better than an EQ6 on a level pier.

Olly

Edited Saturday at 19:57 by ollypenrice

[Mr Spock]

8 minutes ago, ollypenrice said:

Tracking looks fine but this has absolutely nothing to do with where your pier or tripod was pointing.

For the record, I just plonked it down on the patio 🤣 I haven't polar aligned it or levelled the tripod for about 18 months... I know where to put it and it just works.

Yes, if you hold your polar axis still then you can loosen off the mount bolts and swing it around. Plays havoc with my OCD though and would most likely make me feel queasy. I'll settle for level 

[ollypenrice]

1 minute ago, Mr Spock said:

For the record, I just plonked it down on the patio 🤣 I haven't polar aligned it or levelled the tripod for about 18 months... I know where to put it and it just works.

Yes, if you hold your polar axis still then you can loosen off the mount bolts and swing it around. Plays havoc with my OCD though and would most likely make me feel queasy. I'll settle for level 

Certainly a level mount will help calibrate an obsessive-compulsive disorder to zero.  

Olly

[tomato]

I did it all wrong apparently, a cubic metre of concrete and a rat’s cage with the Altair pier but I had my reasons:

1. There was no way I was going to under size the concrete base with a hefty dual rig going on there.

2. Without the cage I would have nowhere to put my mug of tea down.☺️

3. The Altair pier came free with my second hand dome.

[Mr Spock]

Never underestimate the importance of mug space.

[ollypenrice]

8 hours ago, tomato said:

I did it all wrong apparently, a cubic metre of concrete and a rat’s cage with the Altair pier but I had my reasons:

1. There was no way I was going to under size the concrete base with a hefty dual rig going on there.

2. Without the cage I would have nowhere to put my mug of tea down.☺️

3. The Altair pier came free with my second hand dome.

Now we all know that, never in a million years, are you going to reach for that mug, in the dark, while imaging. What could possibly go wrong? You need one of our hot drink-bearing, hands-free hats and, knowing your other tastes, I think the Biggles model would be for you...

 

lly

[saac]

16 hours ago, ollypenrice said:

If a level pier top is needed, please explain how the Mesu seen earlier in the thread, with its pier top tilted to the equatorial angle, can give a periodic error around ten times better than an EQ6 on a level pier.

Olly

It depends on the type of mount used Olly. Alt Az and Dobs need to be levelled for manual use to achieve a reasonable pointing accuracy with setting circles.  Stick electronics on it and you can remove the need for levelling.

Jim 

Edited Sunday at 11:57 by saac

[saac]

15 hours ago, tomato said:

I did it all wrong apparently, a cubic metre of concrete and a rat’s cage with the Altair pier but I had my reasons:

1. There was no way I was going to under size the concrete base with a hefty dual rig going on there.

2. Without the cage I would have nowhere to put my mug of tea down.☺️

3. The Altair pier came free with my second hand dome.

Ingenious - but that cup could do with some bright red anodising to improve your tracking  

Jim