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New User, Conventional wisdom and deliberate misaligning, unbalancing, is it necessary

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Dave Compton Posted: 05-17-2019 10:23 AM

I'm installing my first Paramount, a MyT, in a permanent dome.

As I set things up, I am considering if some conventional wisdom that I have seen here on this forum and elsewhere should apply regarding balance and polar alignment and if I should follow it.

1) Deliberate unbalance of RA to an 'east heavy' load to help the RA tracking/ PEC.  I myself would prefer to get the balance dead on. I don't intend to be in the dome most nights. I will be starting and shutting down remotely. Depending on which side of the meridian that night's target will start on will affect which is my 'east side'. I don't have a means without a visit to the dome to alter this.  So wouldn't balancing as good as possible be the best?  Does deliberate unbalance give any performance gain with a MyT on a permanent pier?

2) Deliberate misalignment to the celestial pole in order to give the declination axis something to push against in one direction.  The adage goes that it is easier to autoguide in declination in one direction only and to misalign the pole to make the declination drift on purpose to assist this.  But wouldn't it be better to be dead on polar aligned and to use protrack as the main tracking mechanism, and a very mild autoguiding aggressiveness setting only to correct occasional disturbances?

... And a question about protrack in that scenario. If polar alignment was set deliberately wrong, and then I ran a nice deep 150~300 point model and engaged protrack, wouldn't protrack cancel the declination drfit and cause it to track more or less on the dec axis, which would negate the value of that drift to the autoguider? The autoguider would see any occasional errors as plus or minus the DEC axis relative to the steady corrections being applied by protrack, and the advantage of DEC tracking in one direction would be lost.

I highly value any feedback because I want to get this install right the first time.

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Dave Compton:
1) Deliberate unbalance of RA to an 'east heavy' load to help the RA tracking/ PEC. 
This is not necessary with a Paramount mount.

Dave Compton:
2) Deliberate misalignment to the celestial pole in order to give the declination axis something to push against in one direction.  The adage goes that it is easier to autoguide in declination in one direction only and to misalign the pole to make the declination drift on purpose to assist this.  But wouldn't it be better to be dead on polar aligned and to use protrack as the main tracking mechanism, and a very mild autoguiding aggressiveness setting only to correct occasional disturbances?
Yes, this can be helpful to ensure that declination corrections are made in one direction.  See this related post for additional information.

Dave Compton:

... And a question about protrack in that scenario. If polar alignment was set deliberately wrong, and then I ran a nice deep 150~300 point model and engaged protrack, wouldn't protrack cancel the declination drfit and cause it to track more or less on the dec axis, which would negate the value of that drift to the autoguider? The autoguider would see any occasional errors as plus or minus the DEC axis relative to the steady corrections being applied by protrack, and the advantage of DEC tracking in one direction would be lost.

The key issue is to avoid declination axis reversals when making autoguider corrections in Dec.  When drift is in one direction (from the deliberate misalignment in the altitude of the polar axis), ProTrack and guiding corrections will be complementary (they'll work with each other, not against each other) to produce optimal tracking results. 

Daniel R. Bisque

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Thanks for the quick and on point reply!

So it looks like best set up is to balance RA about even, and do an accurate polar alignment but don't get too persnickety on altitude +/- 1 arcmin.

Is it necessary to disable the guiding in theskyx guider options in one direction in DEC, or will just leaving the altitude off by an arcmin or so be sufficient to prevent it reversing direction?

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Dave,

If you disable guider corrections in one direction in declination you will lose the ability to dither images. On the other hand I think that if l plunger tension is properly adjusted you will not be bothered by the cross talk issue. There are a bunch of posts re this issue should you actually run into the problem.

Peter R

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Another thing I was wondering about being off on polar alignment is that if you do it on purpose during the ‘accurate’ wizard, it will update your model to assume you centered things precisely.   But I guess you could also just do a quick 6 point decal to establish the PA terms. 

I guess with a slight misalignment and still allowing guiding in both directions, the majority moves will be to one side and keep them tension. 

I have seen the Richard W and others like to go unguided because it simplifies things.  If deliberately misaligned I presume Protrack will account for that and still give good unguided performance. 

Maybe if the tornadoes leave us alone a while I can just try it and see. 

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You will not be able to image with your C11 unguided. A refractor, certainly, but not your C11. Until you get a lot more experience operating your mount, I would run it like everybody else does here. Just evenly balance it and follow the regular APA instructions. Give it a season, learn how to guide, how to massage aggression. Then you can start tweaking things. You’ll have a baseline to compare the changes against. 

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In theory yes.

But you are going to want to do a re-calibration using more like 20 to 25 points on both sides of the meridian. And at least a couple of points above 80 degrees declination (not at 90 degrees but above 80 degrees). This will give TPoint the data it needs to address the change to polar alignment.

Also this is a recalibration run for a portable mount. This is precisely why this recalibration exists in the first place. So that you can do exactly what you are "trying" to. Float the polar alignment terms so that they can be re-established.

Basically a portable recalibration run is nothing more than an automated pointing run picking at least 20 to 25 points. When that is done properly TPoint should be able to address the pointing/tracking rates (when using ProTrack). Of course assuming that the first model you created was at least 50 pointing samples or more, and preferably more like 100 to 150 pointing samples. If you have fewer 50 points just create an entirely new model instead of trying to use a recalibration. Often times creating a new model with 100 points or more is hardly any more effort than creating 25 points. Just takes a bit longer but you should be able to sit back and let the scope do all the work. Or go off and do something else while it is modeling.

Here is a post with exact details on how to do this.

And then the number of points and distribution of points.

This should work extremely well with again the caveat that the original model you created was done with a reasonably extensive number of points first. If not then creating an entirely new model from scratch is in order.

Hopefully this makes sense.

 

Thomas M. Bisque

Software Bisque, Inc.

862 Brickyard Circle

Golden, Colorado 80403-8058

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Thanks again for all the advice and help. 

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