1) The telescope with mount and counterweights has 60kg. The whole thing is balanced, which means there will be no change of the centre of gravity during the observation/imaging.
2) The equivalent surface of mount (from the wind's point of view) is 0.3 m2, Also, lets assume the mount is perfectly rigid, so it does not contribute to the flexure (and FOV shift)
3) the speed of wind gushes is 25km/h (is that severe enough to pack up and go home)?
4) There is no earthquake, walking around pier and/or pulling cables etc.
I think the question may be something like this:
What is the minimum diameter for concrete or steel pipe pier 750 mm high, that will suffer flexure less than 0.3arcsec under above conditions?
Marples - what do you mean you wish Bolton was here - first time I've ever heard anything like that out of your mouth (usually its - damn Bolton is here).
This turned into a tome do dont bore yourself reading from here on if you arent interested - musing of an old Engineer on piers.
I do note that you have an accomplished Structural Engineer in the discussion (Gday Mr Piggo) and probably others. I agree with Troy that the variables involved make it a very complicated calcultation. Troy and I (and probably others - sry I only know Troy) have finite element packages on our computers in front of us that could model it quite well IF we had time. And as I have said before out at the farm it is no good modelling structiral elements unless I know the loads I going to put on it. What scope - how big - weight - GEM or fork (sry if you've discussed this but im at wrok and dont have time to read all the posts - I have to pretend im intersted in undergrads). i'll read them all tonight.
I agree with Bojan that diffeential flexure is the problem - If I have a scope on one side of the mount on say a GEM at a max distance from the mount (ie max moment at the top of the piers) and im taking a 2 hour image the distance the load is from the centre of the pier is not going to change much in 2 hrs - ok there will be slight difference in distance (a bit like the PDelta effect on columns in reverse Troy I suppose) at least based on my empirical experience. If it is a fork mount there is going to be next to no change in moment. In fact thinking about a correctly balanced frok mount should have bugger all moment at the base or top of a pier.
Anyway when I get time and if you give me the dimensions of the piers you want to compare (leave out gussets Pete - I think I know the answer already and I suspect you will be surprised how low the defelctions are). I will do a simple static analysis like - the pier is sticking out horizontal from the wall with a moment at the end and you can compare deflection of conc and steel like the thread says (and this cantiliver model will be far worse than a real world model) - I do think however at the loads I am thinking about - say a 12 inch Meade on GEM (forget about forks it wont happen) the differential deflection and thus differential flexure is going to be anything at all.
I have a 4 inch water pipe with top and btm plates bolted to the floor of my observatory with no conc pier or anything under it - I have a Astro Physics 5 inch, A Tekevue 4 inch and an Orioin ED80 with 4 large skywacther counterweights, motorised filter wheels, CCD cameras etc etc hanging off it and I get no (ie zero) differential flexure over periods of up to 4 hours of imaging the same object. I do realise that others have far more load however but how much are wetalking about -as much as you weigh maybe sry Pete - no joke here.
Imagine your pier solidly bolted to a wall - now stand on the end of it and measure the height from the floor - note that the moment you induce in the pier from this will be far more than it will ever get from a scope (unless you have a 36 inch RC or something on a GEM) - now decrease the moment by stepping say 300 mm closer to the wall and measure again - the difference in these 2 final measurements is what is important- it wil be extremely low and tranforming this change in deflection to arc seconds in a 'normal' focal length telescope (say 2.5 to 3 m focal length) is what we are talking about. Remember too the pixel scale of your equipment (2.5 to 3 metre f/l) when comparing this - is your set up capable of imaging at 1 or 1.5 arc second resolution? maybe but well thats another variable.
I think we as astonomers get a little carried away in design - is bigger better - yep definately but I have never seen pier flexure causing problems in a normal amateur observatory - I dont doubt it has occurred - just i've never seen in it 30 years. What I see more often is flexure induced by overloading (or incorrect side by side loading ) of GEMs.
My 2c anyway. Im sure some will disagree but I can only comment on what i've seen. If i'm off topic - well im old and I spend my days rambling incoherently.
Good points there by Mark... Im a fan of steel (being an industrial metal worker and all)
Only thing I will point out in Marks' post is that even if you have a 36" RC on a GEM, you will still not get as much flex in a pier as if a person stood on the end of the pier when its bolted to the wall.. This is why we use counterweights (along with the fact that we dont want to burn out our mounts motors).
Lets say, you have a mount on a tripod with a 20kg scope, the mount and tripod weigh 40kgs, and when the mounts RA axis is horizontal, the scope's load center distance is say, 80cm off to one side... Can anyone tell me what happens to the tripod if you remove the counterweights at this point? The tripod falls over, or becomes very unstable.
The same goes for a pier.. More often than not there would be minimal lateral force on it, because as 20kgs of telescope starts to hang off to the western side of the pier, 20kgs of counterweight is going out to the eastern side.. Provided you balance your setup correctly, your pier is not under a great deal of strain...
What am I using? I'm using a steel H beam girder for a pier with top and bottom plates welded onto it, and the bottom plate is bolted to a 2'*2'*3' its solid as a rock, and the section of girder I'm using weighs more than the mount, the scope/camera setup, myself and my laptop combined. Better than a round pier? At this level, who really cares? Do I ever notice problems in my images on account of the pier being inadequate? Thats a no.
BTW, if you want to get really fussy, do a Tpoint model. Pier flex and sag is automatically measured and modeled. There are terms both for german EQ and fork mounts.
If the scopes, mounts, and counterweights are all balanced as they should be, ie within normal working range of the mount, the lateral loads on these piers is nominal. Even wind loads will be nominal.
Using Bojan's figures above, 25km/h wind is about 7m/s, and using assumed shape factor of 1.2 for scope/mount etc and applied over 0.3sq.m area produces a force of about 0.01kN. A 100kg person weighs about 1kN, so we're talking 1/100 of the weight of a person. You can see how nominal these lateral loads you're talking about are. And as Bojan intimates, would you be imaging in those sort of winds?
That CN site is recommending about a 219x6.4 CHS section (I adopted sections available here). Putting 0.01kN lateral load on a 750 high pier of that size yields a deflection of about 0.12 arc seconds based on my very rough analysis.
Seriously guys, don't get caught up in the numbers. Use that link above from Cloudy Nights, and just adopt the pier sizes recommended there. They'll be well and truly sufficient and then some, and that's about as much time as you need to spend on it.
You gotta love software compensation! Tpoint is the goods.. Perhaps a discussion for another thread, but it will compensate for almost anything.. even SCT mirror flop
For what its worth, Here is my concrete, slightly coneular pier. No reo, no steel, no welding, cheap, and a fairly weighty PME/12" SCT sits on it with no bother I can detect.
The thread may have drifted slightly from concrete versus steel piers but I think the overall information presented here from all the combined knowledge is very valuable indeed. I have learnt a lot. Again thank you all.
The thread may have drifted slightly from concrete versus steel piers but I think the overall information presented here from all the combined knowledge is very valuable indeed. I have learnt a lot. Again thank you all.
PeterM.
Although my original question was concrete v stell, the resulting discussion has been extremely interesting, so no complaints from me about thread-drift.
However, I'm still uncertain whether I'll build a concrete pier, or a steel one ;-) (But pretty certain I'm stick with my original plan of a steel pier, built as solidly as I can make it!)
As promised I present my initial results on my new Pegasus Pier (I had best declare here and now that a friend of mine also an amateur astronomer manufactures these piers). I have now ran the scope (12inch LX200R on alt/az) on the Pegasus Pier through a hefty multiple galaxy script (105 galaxies in 2 hours) and all seems very well indeed. No evidence of any deflections in the pier causing any issues whatsoever. The night was very steady with the odd 1-2km breeze that would have caught the flexible dew shield extending above the observatory walls, nothing was noted in the images, but they are only 25 second images. My pier is 900mm x 12mm plates top and bottom with 4 gussets top and bottom. The pier has been filled with dry white fine sand. The pier is solidly dynabolted to the concrete floor with 4 x 12mm x 60mm dyna bollts. There are no engineering specs provide as such re the deflection but I think from all figures presented here and my own run last night it would be below 0.5 arc seconds (realising there are other factors to be taken into account as Bojan has correctly noted above). The pier looks superb, it's professional look and sturdiness compliment the telescope. A good investment I am trusting to support my excellent optics. Spinnaker I don't think you will have any issues with a steel pier.
You might like to add extra in for load imbalances and cable drag.
As the mount swings through meridian the cables and any other eccentric load (side mounted) guide cam, finder scope, etc) can change by double.
You cant balance these out completely except with a very complicated set of eccentric counterweights - which are not practically used.
When the camera rotates 180° after a meridian flip a similar thing can happen.
If you are using a large camera, say with 8 filter wheel and depending on your camera angle (the eccentric load may be pointing out or in toward the pier and its cables protruding yet further out or in) this eccentric imbalance can end up being quite a lot more than your wind induced loads - I would estimate by a factor of maybe 100 or more based on my own experiences.
Depending on where the scope is pointing that imbalance differential can be a little (say at zenith) or a lot (say lower on the horizon) - so it is very dynamic.
I am not sure where you calculated the position of the wind load, but depending on the OTA, it could be well in excess of 1m above the top of the pier and I suspect that will increase the deflection in your calcs.
But I agree 25kmh winds mean the end of any imaging session !
750mm height for a pier may be OK for some piers with small scopes where the floor level is also the pier footing level, and low walls, but for most amateur observatories constructed of wood above the ground, and for larger scopes the pier needs to be taller by maybe 300mm to 1000mm to get above the obs floor and maybe another 500mm to provide clearance for the scope and wall clearance to get a reasonable view (say 30-35°) above the horizon.
(much depends on the particular Obs design)
Since the deflection is proportional to the square of the pier length (height) this will affect things considerably, Amateurs need to know that they cant just scale it linearly.
Double the length and the deflection increases 400%, triple it and its up by 900%.
So I would argue that the 8" Nominal Bore pipe (8.625") you used 219mm OD with 6.35 wall thickness may not be sufficient for many situations.
I am truly not trying to be a trouble maker !
But the issue is not always so simple and I am not only trying to talk theoretically here - these are all problems I have had to deal with either for myself or calculations of real life piers that have been constructed at lengths greater than 1.75m - even as much as 2.7m.
Yes Alex - TPoint is wonderful - but it doesnt understand camera rotation yet ! (aka eccentric load rotation). Only rigidty can help that one - in the OTA, adapter Mount and pier !!!
You might like to add extra in for load imbalances and cable drag.
Absolutely. I've been saying all along that there are many variables that affect the outcome of this, and it's just not worth the effort of going into detailed calcs. What I was doing above was directly responding to Bojan's model for the sake of it. It was a quick and simple model to post.
Quote:
Originally Posted by rally
As the mount swings through meridian the cables and any other eccentric load (side mounted) guide cam, finder scope, etc) can change by double.
You cant balance these out completely except with a very complicated set of eccentric counterweights - which are not practically used.
When the camera rotates 180° after a meridian flip a similar thing can happen.
If you are using a large camera, say with 8 filter wheel and depending on your camera angle (the eccentric load may be pointing out or in toward the pier and its cables protruding yet further out or in) this eccentric imbalance can end up being quite a lot more than your wind induced loads - I would estimate by a factor of maybe 100 or more based on my own experiences.
I'm not denying that any of those actions occur. However, this thread is about the pier design. My thoughts on this are:
Wouldn't your mount normally be pretty well balanced about both axes when in a static position? If not, you'd be stressing your mount quite a bit.
If your balance is out by enough to affect the pier, I'd seriously be concerned about your mount. In your mount is one of those massive ones like a Paramount ME with huge capacity, we wouldn't be talking about such small piers and again the pier wouldn't be an issue. It's all relative.
I think the actions you are talking about are perhaps momentum of the moving mount? If all of your gear was reasonably close to perfect balance, there should be negligible lateral loads on the pier. The reaction at the connection of the mount/pier should be practically nothing in shear. There may be some torsion, but that is not a lateral load.
I'd expect there'd be far more movement/slop in the mount than there would be in the pier. By the time the mount settles down, the pier would well and truly be static.
And if you're talking about side by side setups versus piggy-back setups, you need to consider deflection in the plates and all connections too. It's all additive.
And you wouldn't be imaging in those milliseconds/seconds after a bit slew anyway, would you?
Quote:
Originally Posted by rally
Depending on where the scope is pointing that imbalance differential can be a little (say at zenith) or a lot (say lower on the horizon) - so it is very dynamic.
I am not sure where you calculated the position of the wind load, but depending on the OTA, it could be well in excess of 1m above the top of the pier and I suspect that will increase the deflection in your calcs.
But I agree 25kmh winds mean the end of any imaging session !
As I said above, I was simply addressing Bojan's numbers directly. If the centroid of whatever is catching wind is higher, the deflections will indeed increase by the difference of the square of the heights.
Quote:
Originally Posted by rally
750mm height for a pier may be OK for some piers with small scopes where the floor level is also the pier footing level, and low walls, but for most amateur observatories constructed of wood above the ground, and for larger scopes the pier needs to be taller by maybe 300mm to 1000mm to get above the obs floor and maybe another 500mm to provide clearance for the scope and wall clearance to get a reasonable view (say 30-35°) above the horizon.
(much depends on the particular Obs design)
Since the deflection is proportional to the square of the pier length (height) this will affect things considerably, Amateurs need to know that they cant just scale it linearly.
Double the length and the deflection increases 400%, triple it and its up by 900%.
So I would argue that the 8" Nominal Bore pipe (8.625") you used 219mm OD with 6.35 wall thickness may not be sufficient for many situations.
If you look at that CN link we keep referring back to, he correctly provides different pipe dimensions for different heights, for the reasons you mention here.
The 219 diameter pipe I mentioned was quoted specifically for the example used for Bojan's model. I think I've said this many times in this thread before. Change the height, or change the wind speed, or change the area, or change any of the other factors used in the calcs, and the pier size should be adjusted accordingly.
But again, it appears to me that the CN article adequately addresses most of those issues for amateur imagers.
Quote:
Originally Posted by rally
I am truly not trying to be a trouble maker !
No worries. As others are saying, it's an interesting discussion. I'm learning too.
Quote:
Originally Posted by rally
But the issue is not always so simple and I am not only trying to talk theoretically here - these are all problems I have had to deal with either for myself or calculations of real life piers that have been constructed at lengths greater than 1.75m - even as much as 2.7m.
Yes Alex - TPoint is wonderful - but it doesnt understand camera rotation yet ! (aka eccentric load rotation). Only rigidty can help that one - in the OTA, adapter Mount and pier !!!
One thing that seems to have been forgotten in this whole discussion is that the so called figures being used are based on piers without gussets and more importantly, there is no mention of the hundred variables that could affect the test results.
Variable such as scope tube movement, a mount that is slightly loose or of inferior quality and so on.
The reality is that the figures are usleless if the tests were not done on piers independently in a test machine and free from any mount and, attachment to the ground or any other outside influence.
If the results have been gathered from piers attached to the ground and with scopes already on then there are so many variables that could have influenced and skewed the resultts it is not funny.
Surely no one can disagree with sound scientific analysis which it seems the figures some are using as gospel, were not derived from.
Since this thread has started I have looked through many scopes on different piers and noted no movement or deflection at all attributed to the pier on those scopes mounted on gusseted piers.
In fact even on the scopes that I viewed that were on un-gussetted piers the only movement came from inferior mounts and in most cases, scope vibration from the tube which died settled within a second of testing.
It is obvious that the figures eveyone is basing there assumptions on are not based on proper testing or on gussted piers either.
Too much emaphasis is being placed on pier peformance when it is clear for those who look closely, there are clearly other factors which could have skewed these results.
It is OK to question and I would think it is bad practice placing too much importance on partial reasearch and then trying to apply that as a standard.
You say you have looked through many scopes and verified this to all be nonsense.
The whole point of this pier execise is about astroimaging not visual observing !
You have completely missed the point.
Can you tell me what the seeing was in arc seconds on those occasions and how did that affect a long exposure ?
What is the limit and range of your observational skills in determining the FWHM of the stars you see through an eyepiece to validate you claims ?
How much did the FWHM differ according to the diffreent scopes and piers you used ?
For visual observing you can use any old tripod and pretty much any old mount or not even use one at all, the eyes cant detect the small displacements we are discussing here which are in the orders of 1- 6 arc seconds and even if they could, the eyes and brain will compensate for any system movement and even substantial target movement.
The camera will not compensate - it will faithfully record every microscopic movement at whatever your image scale allows and every error - it will bloat or smear your stars and destroy the fine detail in nebulosity by adding noise.
I recall a Seminar where the speaker showed the difference between stars and galaxies that were taken in different seing conditions ranging from about 2-6 arc secs - 2 being good and 6 being about the end of the road for good astroimaging - Most imaging systems (all other things being equal which they usually aren't) are capable of resolving between say 0.4 and 4.0 arc seconds.
He then showed a picture of a human eye that was treated to a blurring filter that effectively added the noise representing the same amount that a perfect star could be blurred to represent the same range of arc second seeing.
The human eye at 2 arc secs was sharp and clear, at 6 arc secs no longer had any iris detail and the eyelashes were no longer recogniseable.
This corresponded nicely with the loss of detail in his astro images and makes for a good analogy.
The astro imagers job is to try and get their system down to a point where the atmospheric seeing is the limiting factor, not the scope, not the focus, not the guiding, not the camera read noise, not the mounts tracking (PE and pointing), not pier induced noise etc etc
Astroimaging requires these levels of stability otherwise we end up with noise in our images.
Any additional noise from mounts that are loose or of inferior quality (as you say), OTA flex and OTA movement due to poor attachment etc etc etc simply add quadratically to all the other noise.
They are all separate problems that each need to be resolved separately and independently.
One does not simply mask the other it adds to all the others.
What we have been referring to is trying to solve the noise in our images and pointing inaccuracies etc that are caused by lack of pier rigidity in observing/imaging conditions and environments that are less than perfect.
The astroimagers biggest job is to eliminate all the noise making problems they possibly can within their own budget and the actions taken in order to get the best image they are comfortable with.
The Pier and its footing is just one of many, but it is the first of many sources starting from the ground up !
It is also the easiest and cheapest of all of them to eliminate.
Only today I was asked about the pipe dimensions necessary for a 48" pier for a requested deflection that was 1/3 to 1/4 of the Mount's approximated flexure under a defined load the person concerned believed the lateral loads we used for his system was probably conservative !
This criteria (given his optical and imaging system) meant that his system would be "mount limited" and that is what he needed to do make the system, such that the weakest link was now his expensive mount because to go the next level would have cost a fortune.
The steel pier dimensions required given its height was 14" Nominal Bore with 15mm wall thickness - based on off the shelf pipe.
He had already done his own calcs and was aware that the pier required was necessarily large.
You seem to have a great understanding of these things - maybe you can provide details of the test machine you refer to and the constraints we need to work to - eg what is minimum movement of the telescope in arc seconds to achieve the resolving accuracy you need for your particular optical system based on your preferred sampling rate and the image scale and the types of targets in mind together with the affects of imaging system rotation and their unresolvable OTA imbalances impacted by pointing in different areas across the sky from the initial "balance".
When it gets down to the numbers we can then talk in "scientific" terms and provide some answers based on historically proven engineering principles rather than rely on hearsay and fundamental misunderstandings of what the issues are.
My only argument throughout all of this is this :
- The pier is an integral part of the imaging platform and it is a ridiculously cheap item to make rigid. In fact apart from maybe some of the cables - it is probably the cheapest major component of your system.
- The Imaging system (Scope, Mount, Camera and accessories) cannot always stay in balance (no matter what you might think) if rotation is involved or pointing across meridian is involved - except in a relatively few special cases and as such needs to be supported by a pier that will not flex beyond a certain limit.
- Other factors affect the stability of the imaging system - wind on the OTA and the pier needs to transfer these to the ground and resist flexure.
1. You can choose the limits of flex and the ultimate image quality you want your system to resolve
2. You can choose the amount you want to pay to achieve this
3. You can choose the amount of effort you want to expend
4. You can choose to believe the engineering maths or not.
1,2,3 are very optional and everyone's situation is very, very different - their system, their budget, their needs, their desired image quality, their observatory, their viewing conditions, their pier height etc . . .
1,2,3 ultimately define how the pier will perform according to your choices and the maths.
4 is more akin to believing the earth is flat or not, you don't have to believe it, but your pier and therefore your optical system will deflect and react and give your images extra noise just the same whether you do or dont believe it !
Its just a question of how much and how much you are prepared to live with - that is all.
Obviously we need a pier (or tripod) so we are really arguing about how much pier we need !!!
It just happens to be a bit more in diameter and or thickness than we think.
I'd just like to make one last post here about these piers. Been having some PM discussions with another member here about the sizing of these things, and more about the variety of different gear going on them. I feel that I need to qualify some more of the assumptions behind my comments just so we're all on the same page.
If you've read this far in the thread, you can tell there are many different factors to consider when designing these piers. If you've read my posts in this thread, you should understand that I've been making certain assumptions on the gear being analysed. I usually try to state what all of the assumptions are, but sometimes they get missed.
So what I've been assuming is that the mount and scopes being supported by the pier are completely balanced about all axes. Think I did mention that a few times, but it's important to reiterate. I'm talking about mounts like EQ6 type scale or smaller. Ones that won't take huge eccentric loads, and won't support bigger and heavier scopes like, I dunno, 12" or bigger?
It has been pointed out to me that some of the larger arrangements may have big eccentric loads - whether it's due to the mount, scope, or cameras supported. These will induce bending moments in the piers as the mount/scope moves, and the pier size will need to be bigger to limit that.
Bottom line... it is very, very, very difficult to accurately analyse all different load cases and combinations on these there. You only need to forget one little thing, or make one assumption, and the detailed analysis is useless. It's not worth skimping on the pier size trying to get the absolute minimum size you think you need.
Whilst i would respect your opinions greatly you really need to re-read the comments I have made again, slowly.
I am in fact referring to imaging as well as visual. It is YOU that has missed the point most respectfully.
Your own comments have more than clearly demonstrated my points and given weight to my concerns.
There are far too many variables that not have been addressed or mentioned.
I have raised several questions which still go unanswered by yourself and others and which play such an important part in how the "test results" were arrived at.
I am happy to back any printed test results as long as they are scientifically validated and all I am asking for is this before making decisions.
I am sure others share the same view.
The request for answers would be considered more than reasonable before investing money on someones unsubstantiated hearsay.
For some reason the simple questions I have asked are worrying some people and being ignored or criticised which really surprises me being that we are all astronomers and should not automatically accept claims without scrutiny.
Rather then being on the defensive, just address the questions raised.
I am sure many people would agree that the answers to these unbiased and neutrel questions have a bearing on how much importance is placed on these so called results.
I again ask the following;
1. Have the figures been obtained from gussetted or ungussetted piers?
2. Were the test results based on a pier attached to the ground and with a mount and scope on? or
3. Were the results based on a pier that was free of outside influence; (ie was it tested independently in a machine or device that could scientifically measure any defelecture or was it the backyard method?)
4. How were the measurements taken and determined? By eye, a computer, camera or stanley tape measure or some other method???
5. rally brings up a very good point about seeing. What were the seeing conditions when these tests were done?
Rally himself indicates that this could make a difference.
This whole thread is based on some figures that were published without scientific backing and without adddressing the above very important facts that without any question DO INFLUENCE THE FIGURES.
Until someone can answer the above questions I think it is silly to place too much importance on figures that have no scientific validation.
In my own practical experience (yes I do have some like other astronomers) I have seen no deflecture in any piers under 1 metre high. Incidently these same piers have gussets and generally have a wall thickness of around 6 mm. I have also seen first hand, multi hour images on the same like piers of many hours duration and there is simply no perceivable defect in the images attributed to any pier deflection.
From my observation the wall thickness means stuff all on piers under a metre high, contrary to unproven claims.
The proof is in the pudding as one would say and I have seen no evidence of any pier deflection in any multi hour images that I have seen. Perhaps someone could provide an image that purports to be pier deflection and with it, details of the mount, scope and pier as well as other details that could play a part in the image making.
Seeing that pier deflection is unproven and so far undetectable in multi hour images, just how far do you want to go and how much do you want to spend to get the NASA standard.
This is just a whole lot of rubbish. Before accepting unvalidated figures quoted as gospel, one really should ask the questions and check the facts before being critical of others. When the simple answers to the questions I have asked have been answered, then we can all have a deep and meanigful discussion
I also think that if you look at many,many award winning images posted around the place alot of these were done using tripods as well in the field. So I think that a well made, gusseted steel pier fixed properly to a solid foundation would have far less deflection than some of these tripods been used.
I will have alot more chance of getting a great image with my gear using one of those well made Pegasus piers that I have installed in my observatory.
My mount, alignment, focus, and I will say focus again, balance, and I will say balance on all axis, seeing and local winds, and user experience are going to let my imaging fail well before my solid professionaly built Pegasus pier will.
99.99% of imagers that use steel piers including some of the worlds best, including quite a few guys I know that get images published are using well made steel piers some home made and some professionally built like the Pegasus pier and they will all tell you that most image flaws are due to seeing, focus and I will say focus again, user error more so than microscopic pier movement.
I have never been told that "last night was crap my images failed because I had 3 arc seconds of pier deflection on every image I obtained yet my mount, focus, balance,seeing,local winds were all perfect and mister worlds best imaging guru was at his best last night".
I have always been told that " My images failed last night because focus, weather, seeing ,mount,balance were having issues,or mister average stuffed up".
Unless we can setup on top of Mt Mauna Kea or the moon for that matter then a well made gusseted steel or concrete pier is going to be more than enough for 99.99% of people.
I am more than happy with my Pegasus pier which is way better than my Giant field tripod that I was using.
I still haven't had the questions answered though from others and with all the hullabaloo it is sad that when challenged with direct questions, asking for scientific validation there appear to be no answers forthcoming on the subject.
Where are those images that show pier deflection or movement?? Heeeellooo..................?
Silence is a loud answer!
The point is well and truly proven that 5-6 mm tube has no issues at all, contary to ill informed belief/opinion.
I am curious though, I keep hearing about 12 mm wall thickness steel tube so perhaps someone can please explain where you can get some of this magical 12 mm tube. Please don't say the scrapyard or Council depot because the chinesse are buying every bit of scrap steel around and forget the Council, you have to go through so much paperwork it is not funny.
There seems to be no tube of any sort anywhere unless it is 4". The commercial major suppliers of steel only sell tube up to 6 mm wall thickness which, you guessed it, comes from China! (cheapest cost tube) You can get the aussie steel but be ready for the 30% increased bill at the end.
You get what you pay for though and that is what people need to remember. The commercial pier and mount makers build to what they think the market can afford and tolerate. If you want a NASA quality pier that is gold plated with anodised fittings and all the gadgets, then you will certainly pay a lot more. The sad thing that has crept into our society is that people don't value quality anymore and all they want to do is pay the cheapest price and cut corners and then whinge when it goes wrong or something doesn't fit.
For what it is worth the the local group pier is good but then you have the Pegasus pier which is obviously far higher quality. I sure if you pay enough dough you can get a better pier again that has the stubby holder, electronic anti earthquake control device as well as the 4" plasma screen and DVD player thrown in but you will pay for it.
I am not sure if it is Pegasus or the other maker but I hear on the grapevine from a reliable source that there is apparently some testing going on by one of the makers to provide some genuine accurate figures on tube flexure/plate flexure (if any) for that pier and once completed, apparently will be published for that pier so I await with great interest on the results, not that it makes any difference.
Last edited by hatman; 18-02-2010 at 09:49 PM.
Reason: typographical error
I don't know about the other guys, but I didn't take too well to your 2 comments about what rubbish you were reading. Perhaps the tone of your posts has yielded the replies they deserve.
I am curious though, I keep hearing about 12 mm wall thickness steel tube so perhaps someone can please explain where you can get some of this magical 12 mm tube. Please don't say the scrapyard or Council depot because the chinesse are buying every bit of scrap steel around and forget the Council, you have to go through so much paperwork it is not funny.
There seems to be no tube of any sort anywhere unless it is 4". The commercial major suppliers of steel only sell tube up to 6 mm wall thickness which, you guessed it, comes from China! (cheapest cost tube) You can get the aussie steel but be ready for the 30% increased bill at the end.
I got my pier made up with that wall thickness. In fact I think it might be 13mm thick. You can get engineering firms to get hold of that material. I paid nearly a grand for my pier. I don't know where you got this information from but clearly this is incorrect. I also know someone else who has a 2.1m length of this for his pier. I hope you are not suggesting we are not telling the truth???
I do agree though that most errors come from everything else other than my pier. I think that I would need a considerable amount of equipment to cause any deflection that would affect my images. Just my opinion of course and anyone is free to disagree. Images tend to be the proof.
Tpoint is the goods.. Perhaps a discussion for another thread, but it will compensate for almost anything.. even SCT mirror flop
