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#1 wargrafix

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Posted 16 January 2014 - 02:52 PM

Hi all. I did a test setup for my weekend session and encountered an issue. My yard has a bit-of a slope. Not very steep though. When I did my 2 star alignment + 1 and then polar align. Repositioned the mount using the handset. When I started searching, my mount always lands a little to the left (if looking through the finderscope)

So very very odd. If I use the handset and center it, the object will stay in the eyepiece just fine. What gives?

#2 Falcon-

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Posted 16 January 2014 - 03:10 PM

You might try adding more alignment stars. I found that the go-to accuracy increased dramatically when I went 2+4 instead of 2+1.

#3 dragonslayer1

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Posted 16 January 2014 - 04:04 PM

This is what I wonder about, did you polar align moving the mount or with the handset? Kasey
" When I did my 2 star alignment + 1 and then polar align. Repositioned the mount using the handset."

#4 guyroch

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Posted 16 January 2014 - 04:33 PM

You always polar align the mount with the adjustment bolts on the mount, not the handset.

Remember that polar alignment is the act of aligning the mount with the pole so this implies adjusting the mount.

Hope this helps,

Guylain

#5 guyroch

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Posted 16 January 2014 - 04:34 PM

Oh, is your mount levelled? Make sure the mount is levelled on that slope yard before attempting any type of polar alignment.

Guylain

#6 Falcon-

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Posted 16 January 2014 - 07:53 PM

You always polar align the mount with the adjustment bolts on the mount, not the handset.


dragonslayer1 might have meant to ask if the handset built in ASPA feature was used. :)

#7 wargrafix

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Posted 17 January 2014 - 07:59 AM

Wow, thanks all. Let me see if I can address it in steps.

I am going to put the mount out tonight,its friday and skies look promising.I will try adding a few more calib stars tonight. the south to north part of my driveway is level, the slight incline is road (east) to the property (west). Should I raise a tripod leg to balance it?

I used the handset to do the aspa feature. I will try to use the adjustment bolts. weird question though if the star moves while I am doing the adjustment, what should I do? Or will the star stay while the the adjustments are being made?

My GOTO has been getting better, but the fine points of getting everything lined up for astrophotography is the final challenge. I too photos and hope to convert to jepg to start posting. I am getting annoyed with not having posted any stuff here yet. You all help alot and I really want to give back.

#8 guyroch

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Posted 17 January 2014 - 08:56 AM

Should I raise a tripod leg to balance it?


Absolutely. If your mount in not leveled to begin with is like running a marathon with crutches.

The best way to leveled the mount, I find, is to remove the mount's head from the tripod and place a level on the tripod where the head would go. Then adjust the tripod legs to get the tripod leveled. Once it's leveled add the mount head back on the tripod. If you place your mount relatively at the same place from night to night just don't touch the tripod leg adjustment you just made and your tripod will be leveled each night as-is :)

Guylain

#9 wargrafix

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Posted 17 January 2014 - 10:08 AM

Hmm, I am excited to try it out. I need to ask though, if the balanced was off along east to west, shouldn't the object be off up or down in the finderscope, not left or right ie north south?

#10 WadeH237

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Posted 17 January 2014 - 10:12 AM

It's important to understand the difference between "polar alignment" and "alignment" and how it affects things.

Polar alignment is a physical adjustment of the mount so that the RA axis is parallel with Earth's rotational axis. You do this on a Celestron mount with the "All Star Polar Alignment" routine. It does not matter if the mount is level or not, but it may make the process a bit easier. If your polar alignment is off, it will affect the mount's tracking. A polar misalignment will not affect goto. The mount is capable of doing accurate gotos even if the polar alignment is far off (it just won't track the object well after pointing to it).

The 2 star alignment that you do through the hand controller is how you sync the mount's internal map of the sky to the actual sky. The accuracy of this alignment will dramatically affect goto performance. It does not affect tracking (since that is related to polar alignment).

After the 2 star alignment, you may optionally do up to 4 calibration stars. Strictly speaking, this is very different than the 2 alignment stars. These 4 stars don't sync the sky to the mount. Rather, they help the mount characterize mechanical error. If you have a perfectly orthogonal system (nobody does), then this step would be unnecessary. By adding these stars, you help the mount to compensate for issues like slight misalignment between where the telescope optics point and where the mount's RA axis points. Personally, I always do 4 stars. It only takes a minute and it gets the best results. The calibration stars have a large affect on pointing accuracy (but not tracking).

In doing both the 2 star alignment and the 4 calibration stars, technique is very important. My experience has been that most of the problems that people encounter with pointing boils down to this.

By far, the most important thing is to make sure that when you look in the eyepiece, you are centering the star that you think you are. For example, if the hand controller wants you to center Alkaid (the end of the big dipper handle), make sure that you are not actually seeing Mizar (the middle star in the big dipper handle) in the eyepiece. The critical thing here is to make sure that your finder scope (or, even better, get a Telrad) and your telescope are pointing exactly the same. To ensure this, go out before dark and point the telescope at something unique on the horizon. The farther away, the better. A tower or an unusual tree top makes a good target. Then, after the scope is pointed at the object, adjust your finder scope (or Telrad, etc.) so that the object is centered there, too.

Note that based on the pointing performance described here, where the object is always in the eyepiece, but off center, it is pretty certain that the correct stars were centered. I've just included the above step for completeness.

Ok, so now you have the correct star in the eyepiece. The next thing is to make sure that you center it properly. First off, an eyepiece with an illuminated reticule is best because you can easily see the exact center of the eyepiece. If you don't have one, then a good tip is to defocus the star so that it's a big donut (or circle if you have a refractor). It's much easier for your eye to identify centering of a big donut than it is for a focused spot.

Finally, now that you have a way to accurately center the star, you need to make sure that you do it consistently every time. And for a Celestron mount, there is one right way. Specically, you must complete the centering process with only the "up" and "right" buttons on the controller. If your last button press is either "down" or "left", you will get some pointing error. The reason for this is that the mount has some mechanical slop (backlash) in the gears. To make sure that you take up this backlash in the same way that the mount does when it points, you need to do it the way that I describe. To do this, I always begin the centering process by hitting "down" and "left" into the star is on the edge of the eyepiece and needs to move up and right. When you do this, you may see the effects of backlash as either a delay when the star moves, or some jumpiness when it first starts to move. The reason that I go down and left all the way to the edge is to make sure that all the backlash is taken up. Then, you can use the "up" and "right" buttons to center the star. If you go past center, then go all the way back down and left to the edge and do it again. Note that it's often helpful to go down to a really slow move rate to make this easier.

One final note is that I mentioned polar alignment first because it was easiest to describe. When you actually do this, the order of operation will be:

1. Set up the mount

2. Turn it on and enter date, time, etc. Different Celestron mounts have different steps here. Note that the date, time and location are not critical for pointing at deep sky objects. If the date, time and location are off, it will affect pointing at solar system objects and it will affect how close the mount gets when it points to where it thinks the first alignment star is. Even if that initial pointing is far off, the alignment will work fine as long as you center the correct star.

3. Do the 2 star alignment

4. Do all 4 calibration stars

5. Use goto to point at a star in the southern sky. This will be the star that you use for the ASPA routine. I like to use a star somewhat near the southern sky near the celestial equator. I believe that you ideally want a star that's 90 degrees away from the North Celestial Pole. But it's not critical. In the summer, I often use Antares or Altair, etc.

6. Do the ASPA routine.

At the conclusion of the ASPA routine, the mount is ready to use. Some people like to power it off and repeat steps 1 through 4. I've found that if you've carefully done everything as I described above, this is unnecessary. Once ASPA is done, I just use the mount.

I hope that this helps.

#11 wargrafix

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Posted 17 January 2014 - 10:22 AM

That was alot of help Wade. :-)

I should say that I do the step you outlined and I have a measure of success. The problem occurs where I am finally going to the target, the target is a bit off, most of the time to the left of the finderscope, or best case, on the left of the eyepiece. if I use the handset and I center it, it tracks fine. all well and good for bright targets but for dim ones, you can see where this is an issue. Its very very weird.

#12 WadeH237

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Posted 17 January 2014 - 12:00 PM

Pointing on the Celestron mounts is very good, but not perfect. I assume that you are using your 9.25" scope. If you are using a high power eyepiece, it may be somewhat normal for the object to be off center, or maybe out of view if high enough power.

You have a couple of options to try and improve it.

First off, if you sync on a bright object in the area you are viewing, it can noticeably increase pointing accuracy. Also, keep in mind that the ASPA routine includes doing a sync on the star that you used for polar alignment. It's possible, if that star is in a different part of the sky, that the mount is still sync'ed there and this could be affecting your results. When in doubt about this, just do an unsync.

Finally, for hunting really dim objects that are at the edge of detectability, I usually use the "Precise Goto" feature. This will have you center a nearby star and then it will do a special slew from that object to the desired target. I've never known it to miss.

-Wade

#13 Peter in Reno

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Posted 17 January 2014 - 12:17 PM

Keep in mind that mirrors in SCT scopes flop when slewing from one object to another. For example, I center/sync a star with the findersccope and the main OTA. Then slew to another object far away, the star would be center in finderscope but in in main OTA. That's because the SCT's mirror shifted (flopped) during slews. I see it all the time.

Like Wade said, during ASPA it does a sync on a "polar" star and after you are done with ASPA, you should "unsync" before slewing to objects. I don't know why Celestron engineers left the "sync" enabled after ASPA.

Also, I think you should re-do the star alignments (2 + 4) after ASPA because you moved the mount by adjusting Alt and Az controls. This can guarantee better GoTos. It worked well for me for my previous CPC0800. Don't forget to "unsync" first before re-running star alignments as explained in Celestron manual.

Like Wade said about Precise GoTo, it's an awesome feature.

Peter

#14 dawziecat

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Posted 17 January 2014 - 01:12 PM

Oh, is your mount levelled? Make sure the mount is levelled on that slope yard before attempting any type of polar alignment.

Guylain


I was faced with doing some imaging in this same situation. I took pains to level the mount . . . but not the chair.

"Don't fall ouut'a ^&*$@ chair!" I said to myself.

Yep. Fell outt'a my chair on the very first night! :crazy: :crazy:

#15 rmollise

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Posted 17 January 2014 - 01:56 PM

Oh, is your mount levelled? Make sure the mount is levelled on that slope yard before attempting any type of polar alignment.

Guylain


Level makes no difference for polar alignment.

OP: Two things right off the bat... Not sure what you mean by "repositioned the mount with the handset," but if you mean you did the polar alignment that way, that is not how you do it. The final part of the AllStar alignment requires you to move the mount with the mount altitude and azimuth adjusters. Also, always do at least three calibration stars for best results.

#16 wargrafix

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Posted 17 January 2014 - 02:35 PM

Ok, you guys got me super excited here. I am spotting a few things to do differently. I strongly suspect that i didn't un-sync and this could result in it getting close to the target but missing a bit.

A question I asked earlier might help me. Obviously, in the moving of the alt-az knobs a little time will pass, how o ensure that i maintain the star on target?

#17 WadeH237

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Posted 17 January 2014 - 03:47 PM

Obviously, in the moving of the alt-az knobs a little time will pass, how o ensure that i maintain the star on target?


I'm sorry. I don't understand the question.

#18 rmollise

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Posted 17 January 2014 - 03:52 PM


A question I asked earlier might help me. Obviously, in the moving of the alt-az knobs a little time will pass, how o ensure that i maintain the star on target?


Just follow the instructions. At the end of the AllStar procedure, the mount will slew off the star. Center it with the alt-az adjusters and...you...are...done. ;)

#19 Peter in Reno

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Posted 17 January 2014 - 04:15 PM

Oh, is your mount levelled? Make sure the mount is levelled on that slope yard before attempting any type of polar alignment.

Guylain


Level makes no difference for polar alignment.


That's true but ASPA likes the mount to be reasonably level so that the mount will most likely be polar aligned on the first try. The more unlevel the mount is the more likely to run two or more iterations of ASPA. There was a very long thread about this and Celestron responded back to me saying that it's better for mount to be leveled for ASPA.

But if you polar align using old school drift alignment, the it makes absolutely no difference whether the mount is leveled or not. It will probably take longer and more iterations to get it polar aligned than if the mount was initially level.

This is what Celestron said to me:

"It's kind of a yes and no answer that is rather subjective. To get a proper ASPA, you do not have to be perfectly level. This is where it gets somewhat subjective though. You can't get a good polar alignment out of a severely off balance tripod. The further away from level that you get, the worse your polar alignment will get. We've had many users in the past who will set up their tripod on a slight hill and not spend much time leveling the tripod and get great results. So it really depends alot of how off balance the tripod is."

Peter

#20 guyroch

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Posted 17 January 2014 - 04:16 PM

Level makes no difference for polar alignment.


I disagree.

Guylain

#21 WadeH237

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Posted 17 January 2014 - 05:03 PM

Level makes no difference for polar alignment.


I disagree.

Guylain


Polar alignment is achieved when the mount's RA axis is perfectly parallel to Earth's rotational axis. It makes no difference at all whether the mount is level or not. It could be hanging upside down from a (very steady) tree branch and still be polar aligned if that criteria is met.

The process of getting the mount polar aligned can be made somewhat easier or more difficult, depending on whether the mount is level or not.

The reason for this is that your are adjusting the mount in altitude and azimuth. If the mount is perfectly level, a change in altitude does not affect azimuth and vice-versa. If the mount is not level, then a change in altitude will affect azimuth to some degree, and a change in azimuth will affect altitude to some degree.

This does not preclude you from achieving polar alignment. You either need to anticipate and account for the movement in the other axis, or you could do additional iterations of whatever method you are using to keep reducing the amount of error in the other adjustment.

It's this latter part that is the reason to get the mount level. But it's not an all or nothing deal. If the mount is reasonably close to level, then you'll have no problems. If the mount is leaning over 45 degrees, then you'll have a harder time of it.

I think that the main thing to remember is that there is not a whole lot to be gained by spending a huge amount of effort leveling the mount. Close is good enough.

This is especially true on a mount like the CG5 mentioned in this thread. The altitude and azimuth adjustments are so coarse, that it's impossible to make really tiny adjustments. I have many Celestron mount, including a couple of CG5s. I would say that it's impossible to get closer than say within 15 arc minutes of the NCP (unless you get lucky) just because of this.

Finally, everything that I've said here is really splitting hairs. For visual use, you can be a couple of degrees off the NCP and it won't result in problematic drift. Even for imaging, as long as you're guiding, you'll be fine with one iteration of ASPA.

#22 rmollise

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Posted 17 January 2014 - 05:06 PM

Level makes no difference for polar alignment.


I disagree.

Guylain


You can disagree all you want. A few minutes considering the geometry of the situations shows you are clearly wrong. ;)

#23 rmollise

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Posted 17 January 2014 - 05:09 PM

I have been polar aligning the CG5 for years. It is more than possible to get the mount right on the money with the adjusters. I can easily get the AllStar star dead in the crosshairs of the Mallincam which yields fairly high "magnification." Similarly, it's no problem to drift align the mount to a point way closer than 15'...

The main caveat? Be careful tightening down the azimuth, as that can throw you back off.

#24 rmollise

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Posted 17 January 2014 - 05:20 PM


"It's kind of a yes and no answer that is rather subjective. To get a proper ASPA, you do not have to be perfectly level. This is where it gets somewhat subjective though. You can't get a good polar alignment out of a severely off balance tripod. The further away from level that you get, the worse your polar alignment will get. We've had many users in the past who will set up their tripod on a slight hill and not spend much time leveling the tripod and get great results. So it really depends alot of how off balance the tripod is."


I have no idea where this guy was going with the business about "off balance tripods." I don't see that this has much/anything to do with level. The only thing being level can do for you is make it a little easier to center the stars in some instances. That is all.

#25 WadeH237

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Posted 17 January 2014 - 05:36 PM

I have been polar aligning the CG5 for years. It is more than possible to get the mount right on the money with the adjusters. I can easily get the AllStar star dead in the crosshairs of the Mallincam which yields fairly high "magnification." Similarly, it's no problem to drift align the mount to a point way closer than 15'...

The main caveat? Be careful tightening down the azimuth, as that can throw you back off.


You may be right. I was thinking about the CGE's azimuth adjustment, which is a pain to work with. Even when drift aligning the mount, it's really hard to get dialed in perfectly.

Still, even on the CG5, if I shutdown the mount and redo the 2+4 stars, then query the polar alignment, it shows errors typically in that neighborhood. I've never tried to drift align a CG5 to compare to what the hand controller reports.






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