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broadsword

Still struggling with GOTO alignment

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I seem to be suffering from a worsening problem with my NEQ 6 GOTO accuracy. I'm fairly comfortable that I'm polar aligning OK now, having carefully levelled the tripod with a spirit level and finding that Polaris stays on the reticule circle throughout the session. I use the 3 star alignment method, having been careful to enter the exact time and right date.

What I'm finding is that the mount follows a similar pattern each time. After starting in the park position, it misses the first star by quite an amount, usually ending up about a quarter of the way from the centre to the edge of the finder scope in a horizontal direction to the left. Following a tip from an earlier post, I loosen the clamps and re-centre the target star by hand before retightening the clamps and pressing enter (this I believe should correct any error in the park position accuracy). I then choose the second star and this one is usually placed very close to centre. However, the third is usually just as way off as the first, in a different direction. After recentering and pressing enter the usual result is alignment failed. Going through the whole process three or four times finally gets an alignment accepted result, but from then on the accuracy is terrible and a lot of drift is observed during imaging.

Am I doing something wrong, or could there be a mechanical problem with the mount? The error seem to be rather systematic each time. It seems to have developed recently and has got a lot worse....any help appreciated.

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Personally I fail to see how loosening the clamps and moving the scope is going to help at all. I would think it would give a incorrect position for the first point. The idea is to teach the scope how far and in what direction it has to travel to reach each point. Moving it without the computer "knowing" doesn't help.

I find that the first star is generally off and the second. However once in action it usually fine.

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You shouldn't release the clutches during or after alignment. First star is always a way off for me too but I believe it's because I don't accurately polar align or set the home position. Second star is usually nearish. After that its all ok (for visual). Never had an alignment fail yet. I think the problem you are getting is due to releasing the clutches.

Once aligned use the polar realignment function to see how good your polar alignment is.

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Like I said,loosening the clutches on the first star was advice from an earlier post and seemed to help the first time. Guess I should go back to not using it.

you both say the first star is usually way off, but how far? Mine's out of the eyepiece (25mm used on a C11). Also, how do I access the polar alignment function?

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Like I said,loosening the clutches on the first star was advice from an earlier post and seemed to help the first time. Guess I should go back to not using it.

you both say the first star is usually way off, but how far? Mine's out of the eyepiece (25mm used on a C11). Also, how do I access the polar alignment function?

It doesn't actually matter how far wrong it is, it is just a guess. Most of the time it is out the eye piece and I need the finder to sort it out. Centering each star enables the computer to figure out what is right. That is the whole purpose of the alignment process.

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It doesn't actually matter how far wrong it is, it is just a guess. Most of the time it is out the eye piece and I need the finder to sort it out. Centering each star enables the computer to figure out what is right. That is the whole purpose of the alignment process.

Also the alingment stars should form a nice big triangle across the sky. If they are too close togethere the alignment wont be as accurate as it could be.

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This all boils down to the home position. Where is it really? OK, we know it is scope up and weights down but how accurately are we setting this position?

When we power-up the handset, it (the h/s), ASSUMES that the mount is in the home position. Precisely.

As there is no feedback from the mount to the h/s, it hasn't got a clue where the mount is pointing.

This is the reason for loosening the clutches to centre the first star. (And only the first star).

After this step you should then park the mount to the home position and power-down.

Now when you power-up, the mount is, as near as damn it, in the 'true' home position.

Without releasing any clutches this time, go through the aligment routine. The stars 'should be' pretty close to central now. Famous last words.

BTW, it isn't necessary to level an EQ mount.

Steve

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I read the earlier post as well - didn´t see any merit in releasing the clutches during alignment. You are effectively moving the star to the wrong position, rather than moving the mount to the correct one.

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Unless the mount has dual encoders loosening the clutch will throw off allignment. Check if the home markers really are home. Was a problem on some celestron scopes a while back. Given they all come from the same factory some production quality sloppyness could have crept onto the skywatcher line. Not unusual for some chinese factories to have nearly 100% labour turnover at holidays

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Unless the home position is important ro you, ie your in an obs, ignore the whole thing of loosening the clutches.

Heres what I do and get spot on alignment all through the night.

Level the mount roughly, it doesnt have to be spirit level accurate.

Get a good polar alignment. Use the handsets cloxk position at least to get a polar fix.

I assume you have aligned the finder, make sure the finder is very well aligned to the optics, should have said this first really.

Set the mount to the home posn. I have marks on my mount that set the position accurately which were done in daylight. These marks mean thes no guesswork about whether the scope is at its home posn in the dark.

Enter lat lon etc

Select two star alignment.

Firts star slew.....usually off by a ways. Use the handest and come to the star in a donsistent manner dor all stars when aligning. Ie approach from left and below. Firts star is usually off.

Assuming you had a good alignment between your finder and the main kptics use the finders crosshairs for alignment. This gakes the guesswork out of whether the star is centred.

Secondstar is usally very close, aligne to it in same manner as first, ie below and left.

Job done.

The star alignment on synscan corrects for cone error only, it doesnt refine the scopes fix onthe sky it only allow the mount to calc. How much cone error is present. Under normal circumstances for visual only and not using anything whacky the cone error will be negligible.

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Well people, there still seems to be differences in views here! I think I'll try most of these things and see which works. Anyone know a good tutorial on making the home position marks?

Also, someone mentioned a polar alignment checking function - anyone know where to find it?

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Different views indeed - I am firmly in the' release the clutches and manually move the mount to centre the FIRST alignment star' camp. This is a simple way of fooling the system (which has NO feedback loop) into believing that it started from a 'perfect' park/home position. It is almost impossible to accurately gauge when the weights are pointing perfectly downwards so, as Spock would say 'you are proceeding from a false premise' which is why so often, the first alignment star is not correctly centred. The simple act of releasing the clutches and manually moving the mount to centre the star and then accepting it with the handset addresses this problem. Obviously this should only be done on the first star alignment with the subsequent second and third star alignments adjusted using the hand controller movement keys.

It is a pre-requisite that as accurate a polar alignment as possible should be carried out and I can confirm that the mount does not have to be levelled first although it does make fine adjustment of the polar alignment a little easier as it stops interaction between the altitude and azimuth axes.

If you have a permanent installation then there is a further bonus in that parking the mount returns it to a now corrected Park position in readiness for the next session.

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I also think the releasing the clutch thing isn't right, however, the correct home position is vital.

tutorial will show you how to get the perfect home position (about half way through the video), there is no need to mark the mount, this method will take minutes each time you set up. I had similar problems to you, untill I followed this video, now I'm rarely out, however, the first star is always miles out but the second is usualy bang on. I carry out 3 star, just to check on accuracy, it only takes a minute. Don't use a watch for the time, I always use my I Phone as its far more accurate

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I know that people say that levelling the mount isn't necessary.....but again, it takes 2 minutes, why not just do it. During setup, the handset always asks "start from park position". Only answer Yes, if the mount has not been moved in any way since the last session. .......not sure if that would make a difference, but again, it takes 2 seconds to get it right.

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I disagree wholeheartidly. Assuming that the gears and steppers do their thing, loosening the clutch on the very first star is the only way to get a proper home position. It has never failed me and tt is logical. If the home position is perfect, the first slew is bound to put the star on-chip. Since the NEQ6 doesn't have any way to determine the home position with any accuracy, the clutch is your friend.

Another thing that can affect is time. One second off puts you 15 arcseconds off target. A minute wrong yields an arcminute of error.

Then, there's the worm gear slack which is easily fixed.

Mount leveling is only important if you rely on polar alignment procedures that slew to a star and let you center it with the dreaded altitude bolts and Az screws.

I find it very hard to understand why such a simple procedure as loosening the clutch for the first star should fail to impress.

All the best,

Per

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Hi Neil, been looking through the thread - I know this is way off topic, but have you tried the alignment with your other OTA - I know the mount will handle the C11, but wonder if you have tried set up, put the 127 on the mount (just to see if the alignment is any closer ???), balance and then try the alignment again with a much lighter payload on - not sure if you've tried this but hope you don't mind the post mate - if your anything like me - it'll be doing your head in - regards Paul.

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Hi Neil, been looking through the thread - I know this is way off topic, but have you tried the alignment with your other OTA - I know the mount will handle the C11, but wonder if you have tried set up, put the 127 on the mount (just to see if the alignment is any closer ???), balance and then try the alignment again with a much lighter payload on - not sure if you've tried this but hope you don't mind the post mate - if your anything like me - it'll be doing your head in - regards Paul.

Hi Paul,

No I don't mind the post at all! You are right, it is doing my head in. I'm desperately trying to image M1, M45 etc before they go and with this godawful weather to lose a precious clear night due to bad alignment is soul destroying.

You raise a point I had been thinking about. I have balanced the mount with the DSLR on the C11, but when I'm aligning I just have the eyepiece on, hence a lot lighter. Could this be enough to put the drives out? I'll try the 127 as you suggest....

Neil

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What has been said in this thread about loosening the clutch on the first star does make a lot of sense. I will give it a try to what advantage I get. I followed the tutorial in the astronomyshed video to mark the home position on my mount. This works for me but the first star is well out of view on any eyepiece so need to use the finder.

The polar realignment feature was something introduced on v3.27 update of the SynScan software I think. It's then under the alignment menu. I find it useful to use as I struggle to see Polaris as my polar scope illuminator doesn't dim.

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Hi Neil, Thanks - I know that set up is critical, but when the mount is "balanced" you have a combined " load " of the OTA + counterweights "bearing down" on the Dec axis, using a lighter payload will decrease the load on the Dec axis - I know when the mount is set up the OTA is Balanced so when the mount is in "Park" mode - all the weight is over the "centre" of the mount, but aligning will place the OTA and the counterweights either side of the "centre" and place an increased downward force when moving to different parts of the sky.

I hope I've explained this ok - just try the lighter payload - it may still be the same (Astronomy is such an intruiging but overwhelming hobby - LOOK HOW MANY TIMES HAS THE "HUBBLE CONSTANT" CHANGED OVER THE YEARS !!!!! :argue: )- just compare the accuracy between the different set ups. I know this is a little off topic and I know that the mount is "balanced" but the EQ mounts (I have the smaller CG5), to me, look as though there's never enough "size" on the actual mount - Celestron have 11" OTA's on them.

The CPC, for me, I think is mounted just about right - the OTA sits a lot closer to the centre of the mount and the SCT is a very short OTA - the OTA and the forks sit over the "middle" of the mount - but lifting it out of the box to place on the mount is about on the limit of my "weightlifting" capacity.

Let us know how you get on mate and hope you get it sorted. Paul.

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Thanks Paul and to all for such a lively debate. To de- clutch or not to de-clutch - that is the question.....I've not seen such a difference in opinion on here before. Are there any gurus we should reach out to? Any way to escalate knotty questions on SGL?

I'll update on how I get on if I ever get out again....

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Much here on the home position. I can only see that as important if you will return the scope to home later on. If you will be packing the scope up at the end of the night the home postion as defined by the goto system seems to me irrelevant.

From the scopes physical home position ie weights down etc, at the start of a goto alignment the scopes electronics basically have a vague idea where the firts star is assuming that the mount is level, its polar aligned etc. it slews to its best guess and you then adjust its aim by using the handcontroller or the clutches. The. Scope then aims for the next star. If you have rleased the clutches ai cant see how the scope compensates for the 2nd star. The electronic would assume its firts slew was super accurate.

Secondly it not easy to lock teh clutches and jit have the scope move out of postion as the clutches bit so youd still have to do some micro adjustments through the handset.

My experience has always been

With a level mount and good polar align that the firts star is off but afte adjustment via the handset the second star is almost bang on. Sometimes almost on the cross wites.

Do what you do tha works, i always use the handcontroller and have no problems at all. The scope probably doesnt return to a perfect home position when parked, for me hat makes no difference as the scope isnst obs based.

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Just a small point ... This is called alignment, it's called alignment because it is aligning, if the first star was in the correct place the mount wouldn't need aligning :D

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From the scopes physical home position ie weights down etc, at the start of a goto alignment the scopes electronics basically have a vague idea where the firts star is assuming that the mount is level, its polar aligned etc. it slews to its best guess and you then adjust its aim by using the handcontroller or the clutches. The. Scope then aims for the next star. If you have rleased the clutches ai cant see how the scope compensates for the 2nd star. The electronic would assume its firts slew was super accurate.

Removing the home position error so that the firmware's slew was "super accurate" is the whole point of the exercise.

The mounts goto accuracy is determined by the summation of a number of potential errors that include: home position error, polar alignment error, cone error, optical distortions, atmospheric distortions etc. The handcontroller will of course do its best to compensate for what ever errors are thrown at it but it can only do this by extrapolating the errors it measures to cover the entire sky. It follows that you will get much more consistent "all sky" results if you can minimise the errors measured as part of alignment. Usually the most significant error contribution will be due home position error. By slackening the clutches and manually correcting the initial alignment goto (and you can only do it on the first) you can remove the majority of this error so that the handcontroller doesn't have to try to compensate for it on subsequent gotos.

As for positioning the mount manually, It doesn't matter if you can't precisely centre the alignment star on your cross hair - you just get it as close as you can and then use the hand controller (or EQMOD) to finish off the job. By doing this the hancontroller now measures only the small correction you've made to fine centre the first alignment star and so it only has to extrapolate this small error when calculating the goto for the second star.

Essentially, the less you give the handcontroller to do - the less opportunity it has to mess up.

Chris.

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Ditto, Chris.

It takes a set number of stepper steps to slew to the first star. If the home position is right, the thing is polar aligned, has no cone error and no flex the first slew would put the star smack in the middle.

Personally, I find the whole idea of setting something up wrong and then adding offsets to compensate for it somewhat repulsive ;)

/per

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I have always loosened the clutches to align the first star. It should be fine. I ask it to slew to the first star - its usually way off so I loosen the clutches - centre the star and then enter it. Its usually way off for the first one - and this also saves time. I previously had an EQ5 pro and that approach was fine and I also loosen the clutches for my first star on my CPC - it even says to do that as a tip in the instructions and the GOTO in the CPC is superb.

Broadsword - if you are after a "guru" look no further than Steppenwolf who has already responded.

Also with the synscan I found that if I didn't closely follow the handsets suggestions for alignment stars it would often fail. Very frustrating. Occasionally I could select a different star to the one suggested and it would work OK but if chose 2 different ones to that suggested there would likely be problems. try to stick as close as possible to stars suggested.

This is where I think the celestron alignment software are better than the synscan

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