Leveling a Pier: who's right ?

[StevieDvd]

22 minutes ago, ollypenrice said:

What would you say to someone who asserted that only piers painted red could provide perfect polar alignment?

Olly

That would be rediculous.

People (possibly Peter Piper) prefer purple painted piers providing perfect procedural polar alignment.

[Mr Spock]

Piers have to be painted white. It’s some kind of law I think. 

[Albir phil]

1 hour ago, ollypenrice said:

What would you say to someone who asserted that only piers painted red could provide perfect polar alignment?

Olly

Very little, leave them to it😵‍💫

[Xilman]

I am a heretic. Let's get that out of the way straight away.

An earlier poster said that all too often, too many of us obsess over inconsequential details and gave an example of seeing conditions outweighing any supposed benefits of precise alignments.

Personally I believe that polar alignment is over-rated, within reason. These days of autoguided mounts with movement in both axes will keep an object centred essentially for ever, which is fine for visual observation. Field rotation will be a problem only for long exposures and seriously misaligned axes. Even then, a field rotator will compensate. Stacking multiple exposures deals with moderate amounts of field rotation without any difficulty whatsoever.

An alt-azimuth mount is about as polar un-aligned as is possible (unless you are based at the geographic poles, of course). Essentially all professional telescopes built in the last fifty years and many amateur instruments (for example the SeeStar) have alt-az mounts; all take superb quality images.

[ollypenrice]

19 minutes ago, Xilman said:

 

An alt-azimuth mount is about as polar un-aligned as is possible (unless you are based at the geographic poles, of course). 

Don't forget the equator!

lly

[Swoop1]

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)

[Xilman]

2 minutes ago, Swoop1 said:

...

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?

See above for my comments which apply if your scope has an autoguider and your mount can be driven in both RA and Dec.

"Massively" is gross over-statement. "Trivially" or "negligibly" is much more accurate under almost all circumstances. See also my comment about driven alt-az mounts.

And don't call me Shirley.

[saac]

32 minutes ago, Swoop1 said:

You spend time reaching perfect polar alignment 

There is your answer Swoop1.  In adjusting your mount to reflect your local latitude and polar aligning you have done what no amount of levelling could ever do.  It is the latitude adjustment and polar alignment above all that is important - in the equation of "everything being alright",  the symbol for levelling the pier does not feature. 

Jim 

[Ags]

Surely a pier should be pointing at Celestial north, not at the center of the Earth?

[Elp]

I used to level my tripod. Now I don't as long as it's fairly "flat" and the balance won't tip any of the legs.

The only reason I see to have a level base is if you're really OCD and need your azimuth adjustments to be near enough perfectly left-right and altitude up-down. Once PAd, none of this matters.

I think it would affect an alt az mount slightly.

[Elp]

5 minutes ago, Ags said:

Surely a pier should be pointing at Celestial north, not at the center of the Earth?

Depends what end you're looking at...

[Xilman]

1 minute ago, Elp said:

Depends what end you're looking at...

Which end of the Earth you mean?

The Ozzies, for example, might not want to look at the NCP. Too much rock in the way, much like my eastern horizon.

 

[Elp]

1 minute ago, Xilman said:

Which end of the Earth you mean?

The Ozzies, for example, might not want to look at the NCP. Too much rock in the way, much like my eastern horizon.

 

I'd be concerned if my pier was not mounted vertical into the ground (layman's direction toward the centre of the earth)...

[Xilman]

5 minutes ago, Elp said:

I'd be concerned if my pier was not mounted vertical into the ground (layman's direction toward the centre of the earth)...

Ok, Fairy Nuff.

Pointing it at the relevant celestial pole has some very useful advantages. No need for a meridian flip on a GEM for a start.

 

[bwj]

I will add something here, and being comparatively inexperienced, maybe it doesn't apply. 

The large majority of posters on here assume a GEM or equivalent that can be polar aligned. As was mentioned, there are a lot of alt-az mounts out there, and there are a lot of people who don't or can't use autoguiding for various reasons.

That is my case. For this situation, having the mount base level is very important to getting good go to and tracking. It seems a lot of the models in the computerized mounts assume you are starting level. It also seems to me that for those with manual mounts, leveling makes it easier.

Clear Skies@

Bill

[Ags]

5 hours ago, Elp said:

I think it would affect an alt az mount slightly.

It has a big effect, with my AZ-GTi I take care to make sure the mount is as level as possible. It's irrelevant for EQ mounts, I agree.

[saac]

17 hours ago, bwj said:

I will add something here, and being comparatively inexperienced, maybe it doesn't apply. 

The large majority of posters on here assume a GEM or equivalent that can be polar aligned. As was mentioned, there are a lot of alt-az mounts out there, and there are a lot of people who don't or can't use autoguiding for various reasons.

That is my case. For this situation, having the mount base level is very important to getting good go to and tracking. It seems a lot of the models in the computerized mounts assume you are starting level. It also seems to me that for those with manual mounts, leveling makes it easier.

Clear Skies@

Bill

Yep we assumed we were talking about GEM mounts - these do not need level piers. Alt AZ mounts on piers do need to be levelled if using any form of goto or even manual setting circles. Similarly Dobs, as discussed on a separate thread, also need levelling where goto or manual setting circles are in use. Of course if you have one of the new purple piers you can ignore all of this. 

Jim

[Mr Spock]

If my mount isn't level, it won't track properly. It may track in RA ok if it's still polar aligned, but Dec will drift. When it's level, it will track for hours. Same goes for the EQ platform the Dob is on.

I 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.

[Xilman]

11 minutes ago, saac said:

Yep we assumed we were talking about GEM mounts - these do not need level piers. Alt AZ mounts on piers do need to be levelled if using any form of goto or even manual setting circles. Similarly Dobs, as discussed on a separate thread, also need levelling where goto or manual setting circles are in use. Of course if you have one of the new purple piers you can ignore all of this. Jim

Not strictly true, for all kinds of mount, if autoguiding in both axes is possible.

It really doesn´t matter where the axes point, or even if they are at right angles to each other, as long as camera can see the same star from one second to the next and as long as the computer can tell the mount where to move so as to keep the guide star at the same place in the FOV. How the computer knows that is, of course, learned from a calibration phase before guiding for real. Ok, you may need to calibrate at the start of each observing session if the mount is positioned differently each time, as is typical for portable set-ups.

[Xilman]

3 minutes ago, Mr Spock said:

If my mount isn't level, it won't track properly. It may track in RA ok if it's still polar aligned, but Dec will drift. When it's level, it will track for hours. Same goes for the EQ platform the Dob is on.

I 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.

Exactly, which is what I just stated in the post which overlapped in posting time with yours.

[saac]

Just now, Xilman said:

Not strictly true, for all kinds of mount, if autoguiding in both axes is possible.

It really doesn´t matter where the axes point, or even if they are at right angles to each other, as long as camera can see the same star from one second to the next and as long as the computer can tell the mount where to move so as to keep the guide star at the same place in the FOV. How the computer knows that is, of course, learned from a calibration phase before guiding for real. Ok, you may need to calibrate at the start of each observing session if the mount is positioned differently each time, as is typical for portable set-ups.

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 

[Xilman]

Just now, 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 

I did say that you may need to recalibrate at the start of each session.

Because my mount doesn't have absolute encoders I take a sighting image at the start of a session, plate solve, and use that to let the software (Maxim DL in my case) know the orientation of the telescope to within a few arc seconds. I tend to re-solve after a large slew to ensure the pointing accuracy remains at the few arcsec level.

 

[saac]

15 minutes ago, Xilman said:

I did say that you may need to recalibrate at the start of each session.

Because my mount doesn't have absolute encoders I take a sighting image at the start of a session, plate solve, and use that to let the software (Maxim DL in my case) know the orientation of the telescope to within a few arc seconds. I tend to re-solve after a large slew to ensure the pointing accuracy remains at the few arcsec level.

 

I put manual setting circles on our school's 16 inch Dob a few years back - they are fairly big, coming in at 33 inch in diameter so a bit of an art using them.  I've also fitted encoders to each axis, and these feed the coordinates to an LCD display. When using the setting circles for the first time I was disappointed how poor the pointing accuracy was until I realised that I had been a bit casual with levelling of the scope.  While it's a bit of a pain, we have since found that the time we take setting up pays dividends with pointing accuracy. 

Jim

Edited June 21 by saac

[Mr Spock]

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!

 

[Pompey Monkey]

2 hours ago, Mr Spock said:

If my mount isn't level, it won't track properly. It may track in RA ok if it's still polar aligned, but Dec will drift. When it's level, it will track for hours. Same goes for the EQ platform the Dob is on.

 

This does not make any sense to me.

If you are polar aligned, there will be no drift in declination. That's what polar alignment does.