Jump to content

Banner.jpg.b89429c566825f6ab32bcafbada449c9.jpg

A pier question!


Andrew INT

Recommended Posts

After dithering about for ten years, I have finally decided to start building my own observatory. The first step was to order a telescope pier (and twenty bags of ready mix cement)

Have put in a reasonable amount of research, I purchased an altair skyshed pier which is yet to be set in cement until the weather warms up a little more.

My question is this: do any owners have vibration issues with this pier? The reason I ask is that I came across this link today which has made me re think things a little more: https://youtu.be/AOeLnecOMeg The guy is talking about the "rat cage" part of the pier head. Is this REALLY an issue, or just (mainly) a sales pitch angle.

Hopefully someone will help put my mind at rest that my new purchase is actually ok!

 

(Edited for typos)

Edited by Andrew INT
Link to comment
Share on other sites

They are trying to sell a not too cheap pier, which they claim is better....

But after reading around, I made my own using 2x2M tubes (air-con ducting 250mm & 150mm diameters) filled with concrete. A bit of a pain to drill the hole, but it is rock solid. 

  • Like 1
Link to comment
Share on other sites

Yes, there was a bit of sales spin, but nothing sounded too outlandish.  I just  wondered if some features,  such as the "rat cage" do produce any noticeable issues. Im pretty pleased with the build quality of my skyshed, but I havent tested it yet.

Link to comment
Share on other sites

My pier has the 'rat cage' but there are rat cages and rat cages.

I have seen some using 150mm long x 3 bolts at full length - no matter how sturdy the pier the rat cage will wobble.

The thicker the bolts, the more of them and the smaller the gap between top plate and pier the less it will wobble - simple physics.

I am not saying mine is perfect but it uses 8 x 15mm bolts and the gap between top plate and pier is about 30mm

This is my guide trace from a breezy night.

For ease of adjustment and fabrication the rat cage takes some beating.

 

 

 

post-33941-0-43512900-1452886176.jpg

  • Like 1
Link to comment
Share on other sites

If I have the right video in mind another member described it as 'snake oil,' which struck me as being about right.

People go to a lot of trouble to make their pier tops adjustable so as to be levelled. In fact a mount can be perfectly polar aligned when the mount is not fitted to a levelled pier top. As I've often pointed out, up- market Takahashi mounts have no facility for levelling - because it isn't necessary.

My own take on the 'snake oil' video was that the ground fastenings of the wonder pier being purveyed were too close to the pier itself. I always make piers with a reasonably large footprint.

Olly

  • Like 2
Link to comment
Share on other sites

I think I know the video in question and whilst I agree that there is no need for the rat cage, I don't think it's necessarily as detrimental as the vid makes out. It also made me laugh when he started banging on about the welds being part of the tentioning (i'm paraphrasing here). For crying out loud, the distortions due to the welds are unavoidable and there is next to no way of replicating the same "warp" with every pier. I think he's done the diy astronomer a great dis-service insinuating that we are nearly all incapable of building a descent mount. for the money he charges, I could probably build a handful.

 

  • Like 2
Link to comment
Share on other sites

I have the Skyshed pier and have no problems with it at all using an NEQ6, I like the design, it's is easy to install.

I did have a bit of problem when I previously had a CG5 GT on the pier as being smaller I could not see through the polarscope as the top pier plate was right where my chin needed to go, but once I swapped that for an NEQ6 that problem went away.  

Works better with a piggy backed guidescope than a side by side arrangement as less risk of scopes clashing with the pier plate.  

Contrary to what has been said about not needing the pier level, I did accidentally "slightly unlevel my top plate" once when removing the mount for Astro camp (this is because the top plate needed to be removed in order to get the central rod out).  I had not realised I had done this and it took me quite a long time to fathom out why I could not get a decent polar alignment or do an alignment procedure properly.  I also could not do a polar alignment using Alignmaster until I levelled that top plate.  

I don't remove the mount any more and no further problems.

 

Edited by carastro
  • Like 1
Link to comment
Share on other sites

29 minutes ago, Daniel-K said:

if the stars are round why stress ?:happy6:  

Because round stars don't indicate good guiding. Random errors will produce round stars - but large round stars.

10 minutes ago, carastro said:

I have the Skyshed pier and have no problems with it at all using an NEQ6, I like the design, it's is easy to install.

I did have a bit of problem when I previously had a CG5 GT on the pier as being smaller I could not see through the polarscope as the top pier plate was right where my chin needed to go, but once I swapped that for an NEQ6 that problem went away.  

Works better with a piggy backed guidescope than a side by side arrangement as less risk of scopes clashing with the pier plate.  

Contrary to what has been said about not needing the pier level, I did accidentally "slightly unlevel my top plate" once when removing the mount for Astro camp (this is because the top plate needed to be removed in order to get the central rod out).  I had not realised I had done this and it took me quite a long time to fathom out why I could not get a decent polar alignment or do an alignment procedure properly.  I also could not do a polar alignment using Alignmaster until I levelled that top plate.  

I don't remove the mount any more and no further problems.

 

I don't use Alignmaster and don't know how it works, but there is absolutely no doubt that mounts do not, in principle, need to be level. Try this thought experiment: take a perfectly aligned mount and get Harry Potter to hold it permanently in place by magic. In this situation you can remove the pier or tripod completely and Harry's magic will keep it perfect. Or you could shorten the tripod legs so they no longer touched the ground and then you could use the levelling adjusters to point the pier or tripod wherever you liked. The point is that this will have no effect at all on the polar alignment.

The best fast PA routine bar none is Takahashi's and their tripods have fixed legs.

Olly

  • Like 1
Link to comment
Share on other sites

12 minutes ago, ollypenrice said:

Because round stars don't indicate good guiding. Random errors will produce round stars - but large round stars.

I don't use Alignmaster and don't know how it works, but there is absolutely no doubt that mounts do not, in principle, need to be level. Try this thought experiment: take a perfectly aligned mount and get Harry Potter to hold it permanently in place by magic. In this situation you can remove the pier or tripod completely and Harry's magic will keep it perfect. Or you could shorten the tripod legs so they no longer touched the ground and then you could use the levelling adjusters to point the pier or tripod wherever you liked. The point is that this will have no effect at all on the polar alignment.

The best fast PA routine bar none is Takahashi's and their tripods have fixed legs.

Olly

Not ideal if you're on the side of a hill, but Iget your point ;) 

Link to comment
Share on other sites

10 hours ago, auspom said:

Not ideal if you're on the side of a hill, but Iget your point ;) 

:icon_biggrin: It would have to be quite a steep hill, in reality. This is actually metioned in the manual. And if Tak users live too far north for the rather limited adjustment in altitude they routinely put something under a foot to tip the tripod.

By the way, I don't see how Alignmaster could have any knowledge at all of how the altitude angle was acheived (whether by tilting the pier/tripod or using the adjusters. The result is identical. Rather intelligently the levelling bubble on Avalons only runs east west, it isn't a circular bubble level.)

Olly

  • Like 1
Link to comment
Share on other sites

I still can't get my head around how a mount can follow the Earth's rotation unless it is level.  

You have the latitude bolts for tipping the mount up and down in a forwards and backwards manner, but what if the mount is unlevel sideways, how on Earth (excuse pun) does the RA follow the Earth's rotation then?

I can only speak from what works and what didn't work for me.  As soon as I had the plate level then my PA worked, I could Polar Align with alignmaster and GOTOs went to where they were supposed to.  Nothing worked as it should before I realised the plate was unlevel.  

Carole 

 

Link to comment
Share on other sites

Hi Carastro,

I suppose that by altering the mount alt az when polar aligning, you are effectively leveling the mount. The axis will be correctly aligned even though the pier or tripod is not level.  However my heq5 has only limited parameters for adjustment to the pier head cant be TOO unlevel/ off north.

I thinks thats what is being said within the thread?

Link to comment
Share on other sites

48 minutes ago, carastro said:

I still can't get my head around how a mount can follow the Earth's rotation unless it is level.  

You have the latitude bolts for tipping the mount up and down in a forwards and backwards manner, but what if the mount is unlevel sideways, how on Earth (excuse pun) does the RA follow the Earth's rotation then?

I can only speak from what works and what didn't work for me.  As soon as I had the plate level then my PA worked, I could Polar Align with alignmaster and GOTOs went to where they were supposed to.  Nothing worked as it should before I realised the plate was unlevel.  

Carole 

 

I know it can be odd at first but this isn't really hard to grasp.  

What does Polar aligned mean? It means that the mount's RA axis is parallel with the earth's axis of rotation. So if, in imagination, you took out your polarscope once the mount was aligned and fitted a steel shaft through the middle of it, fixed at each end to your observatory, it would then be impossible for your polar alignment to be imperfect. (It would get in the way of the scope but we're just thinking aloud here.)

So now your mount has a steel shaft through its RA axis and cannot be moved by any means from perfect alignment. Now unbolt the pier from the floor and loosen the polar alignment bolts. In fact throw them away!! You can now tilt the pier forwards, backwards and sideways and the PA remains perfect. So there is no relationship between the angle of the pier and the PA.

The main reason for levelling is simply to set the 'clock' in the polarscope reticle to vertical. (On Taks, with their potentially tilted tripods, you do this by means of a bubble level on the RA housing.) The other reason is that, in doing drift alignments, there is less interaction between drift tests in the south and then in the east or west. Maybe this is what Alignmaster didn't like when the mount wasn't level.

My real point is that in an observatory mount there is no need to compromise a pier's rigidity by making it highly adjustable. Better rigid than adjustable if you can't have both.

Olly

  • Like 3
Link to comment
Share on other sites

Consider the opposite way where your mount was fixed and had no adjustment bolts. If your pier/tripod started perfectly horizontal  you would need to adjust it to centre the mount axis with the NCP. 

It does not matter too much if you adjust the pier or the mount as long as the axis ends up correctly aligned, it's just a little easier (and cheaper) to use the mounts adjusters.

 

 

 

 

 

 

Link to comment
Share on other sites

52 minutes ago, ollypenrice said:

Dec isn't level. If Dec is level you'll be looking at the horizon!

Olly

I think Carole means east / west, anyways for the time it takes to level you might as well do it, I have a wedge (was that a big sigh I hear from Olly :) ? ) that doesn't perform too well if it's not level East/ West, North / South obviously makes no odds.

On the three tons of concrete subject, if your imaging something like Saturn and jump up and down near your pier the image will jump about no matter how much concrete you use, if you just stand your tripod on the ground and view it from a distance while imaging the image will be no worse than on a pier IMHO

Dave

  • Like 1
Link to comment
Share on other sites

I have a Pulsar pier (The one in the video) and TBH the lack of adjustment doesn't bother me. I made sure the mounting block it was going on was reasonably level and after that it was a first iteration with the Eqmod PA tool then drift align in PHD2.

TBH I need to give it a few more iterations of drifting and then a 3 star alignment, when we have a clear night with little or no Moon. Yearh, right :(

Link to comment
Share on other sites

I agree, the pier most certainly does not have to be level. The way I describe this to non-believers is this:-

Imagine an infinitely long round pole with a diameter that is a perfect fir in the polarscope's mounting hole. Assume that this pole cannot be bent and that it reaches light years into space aimed at the North Celestial Pole (NCP). Now slide the mount (an EQ6 will do fine) onto this pole through the polarscope's mounting hole. The polarscope hole is now pointing at the NCP.You can rotate the whole mount around the pole to ANY angle you like and it will remain polar aligned. So, let's go wild and rotate the mount to , let's say, 31.6 degrees from vertical and get a local builder to build us a wall that touches the the flat base of the mount and then blot the mount to the wall at this crazy angle. The mount is still polar aligned!

Is there an advantage to having a level mount? Yes, a perfectly level mount will not show any interaction between the azimuth adjustments and the altitude adjustments when you carry out a polar alignment adjustment but really, this is no biggy!.

  • Like 1
Link to comment
Share on other sites

It's also useful if you're setting up on three marks on the ground as I do with the SW Star Adventurer, if I use the built in bubble to level it then Polaris is always visible in the Polar scope and just needs a small tweak to PA.

Obviously straying from the OP's original question a bit but just thought I'd mention it :)

Dave

Link to comment
Share on other sites

3 minutes ago, carastro said:

OK, I get the polar aligned bit, but I am still to be convinced about whether GOTO would then work accurately if it's not level.  

Carole  

I think it's one of those thing's it's best not to think about at my age, just set up level and save the brain ache :)

Dave

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.