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3 Star Alignment issues with Atlas EQ-GOTO

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#1 chitown

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Posted 21 May 2009 - 07:29 AM

So last night i was finally able to put polaris in the little circle of the polar scope.

The weight end went up and the scopes virtually down.

I selected Vega, and the mount started to slew... banging my C6 on the tripod leg and then mis-aligning it of course.

I removed the eyepiece from my Tak and diagnol from my C6 to make space, selected next star and same thing. One of the ends of my C6 would end up banging the tripod leg.

So i thought, possibly the default position is weight end down, scopes up. This time polaris was not in the little circle of the polar scope, but same hour position as the polarfinder software provided.

I selected Vega again, this time the mount moved in more desireable location. Right near Vega, but off target.

I am not sure what and where I am doing wrong. But seems like the default position should be weight end down.

Any ideas?

#2 neptun2

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Posted 21 May 2009 - 07:47 AM

First i recommend you to make the polar alignment as described in astro baby's webpage:
http://www.adur-astr...HEQ5/HEQ5-1.htm

I know that it is for sirius and not Atlas but the polar scope should be the same and differences are not big i hope. After you finish with setting the date and time using the setting circles and you managed to put polaris into the circle using the azimuth and altitude adjustment you have pointed correctly to the north celestial pole.Now all you need to do is to release the ra index scale lock and the RA and DEC locks and manually slew the scope to it's home position as described in the user manual of synscan. Then tighten again the RA and DEC locks and continue with alignment following the instructions in the user manual. I recommend you to make 3-star alignemnt and to use reticle eyepiece to center the stars better or if you do not have reticle eyepiece use eyepiece with narrow FOV. You can also slightly defocus the star to make it bigger and easier to center.

Edit: Polaris needs to be in the circle only in the beginning when you make polar alignment. The idea here is to calculate using the setting circles where should polaris be at the day and time when you are making the polar alignment. Polaris is not at north celestial pole but near it. The polar scope is made in such way that when polaris is in the circe the mount is pointing to the NCP. So if your calculation with the setting circles for the psition of polaris is correct and you put it into the circle then your mount is pointing to the NCP and only if you touch the azimuth or altitude adjustment or your tripod is moved your polar alignment will be broken. So do not worry that after the polar alignment polaris will no more be in the circle.This is not problem.

#3 rdegoutier

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Posted 21 May 2009 - 07:53 AM

After putting Polaris in the correct position on the circle (this gets the mount aligned with the NCP), you need to set the scope so that it is (roughly) pointed at the NCP. This would be with the weight end straight down and the OTA in line with the polar scope.

From your position, last night at 9:30 PM, Polaris should have been just about at the top of the circle, or 12:00 position. If you have a Synscan HC, it should give you Polaris position after you complete setup.

#4 chitown

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Posted 21 May 2009 - 07:56 AM

This part i do not understand:

"Now all you need to do is to release the ra index scale lock and the RA and DEC locks and manually slew the scope to it's home position as described in the user manual of synscan. Then tighten again the RA and DEC locks and continue with alignment following the instructions in the user manual"

Can you explain step by step..

#5 chitown

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Posted 21 May 2009 - 07:58 AM

Not getting this part, please explain to me:

"you need to set the scope so that it is (roughly) pointed at the NCP. This would be with the weight end straight down and the OTA in line with the polar scope. (It cant be, as if i move the RA to move scopes, polaris will move away from the circle of the polar scope reticle.)

AND

If you have a Synscan HC, it should give you Polaris position after you complete setup."

#6 neptun2

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Posted 21 May 2009 - 08:06 AM

Ok i will try to be more precise. ILook at his page:
http://www.adur-astr...HEQ5/HEQ5-3.htm

This is the final step of plar align which you make on the field. Read carefully the "Align to plaris part" of this page. After you have done this just release the RA index scale lock, manually slew the scope to it's home position as described in user manual, tighten the RA and DEC locks and follow the instructions in user manual to make the 3-star align.

#7 David Pavlich

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Posted 21 May 2009 - 08:11 AM

Step 1: Make sure that you start with home position, scope pointed north, counterweights straight down.
Step 2: Align the polar scope by moving the RA axis until Polaris aligns in the circle, adjusting with the Alt/Az adjustments.
Step 3: Return the scope to HOME position.
Step4: Do 2 stars on one side of the meridian and the third star on the other side. This takes care of cone error. Use a high power eyepiece, preferably a reticle eyepiece.

Now, enjoy your gotos!

David

#8 rdegoutier

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Posted 21 May 2009 - 08:12 AM

Not getting this part, please explain to me:

"you need to set the scope so that it is (roughly) pointed at the NCP. This would be with the weight end straight down and the OTA in line with the polar scope.

AND

If you have a Synscan HC, it should give you Polaris position after you complete setup."


When you align the mount, you are setting its axis to point to true north. This is done with the OTA in horizontal position. Once this step is completed, loosen the clutches and slew the telescope so that it is pointed (roughly) to Polaris or the NCP. Weight bar will be pointing down, OTA will be on the top, and your OTA and Polar Scope will be pointing in the same direction. This is called the Park position, and you must start from this position before beginning aligment.

When you finish setup from your hand control, the HC screen will tell you what position Polaris should be in your Polar Finder. Alternatively, there is a neat little program called Polarfinder by Jason Dale that does this very nicely. You can get this at: http://myastroimages..._by_Jason_Dale/

#9 chitown

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Posted 21 May 2009 - 08:14 AM

ive seen this. My mount does not have "date and time" circle.

#10 chitown

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Posted 21 May 2009 - 08:17 AM

Step 3: Return the scope to HOME position.


But if i do this, then polaris will escape the reticle circle of the polar axis scope?

#11 chitown

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Posted 21 May 2009 - 08:21 AM

When you finish setup from your hand control, the HC screen will tell you what position Polaris should be in your Polar Finder.


Where is this information displayed, is it the PolarisHC prompt?

#12 rdegoutier

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Posted 21 May 2009 - 08:38 AM

[quote
Where is this information displayed, is it the PolarisHC prompt? [/quote]

Yes. My scope is put away, but I believe it is the second number.

To clarify the procedure(s), the Polar alignment step has nothing to do with the star alignment procedure, other than pointing your mount accurately to the NCP. Once this step is done, put the caps back on the Polar Finder and don't look at it again. As long as you don't move your tripod, it will stay positioned correctly.

#13 Skylook123

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Posted 21 May 2009 - 08:42 AM

Forgive me if, in my humble opinion, folks make the whole polar alignment exercise into a mental and physical contortionism.

First preliminary comment is that the Atlas does not come with the date-time circles, so there are two alternatives; the fuss and bother of trying to align the RA setting circle and OTA to get the little circle in the right location, or fuggedaboutit and do it the easy way, IGNORE THE LITTLE CIRCLE. Too much irrelevant information.

1. Set up mount so it points as close as possible to True North in azimuth and your latitude in elevation. Don't worry about home position yet. Leveling the mount does help the whole thing work easier.

2. Polaris needs to be on the big circle in the polar scope. All the convoluted instructions on getting the little circle oriented are unnecessary. The hand controller, when the correct date and time are entered, tells you where the little circle should be (the second number in the polar data). Or, use a planetarium program with the current date and time and notice where Polaris is with respect to the North Celestial Pole. I have a target circle of 1.5 degrees I center on NCP, Polaris lands on it.

2. Either use the hand controller Polaris location, which takes into account the horizontal and vertical flips in the polar scope refractor, or mentally flip the planetarium orientation in both axes. That's where Polaris should appear on the big circle in the polar scope. Piece of cake. Much easier to do than to type up.

3. So, you set up the mount, you know where Polaris should appear on the big circle from the hand controller or from your planetarium program, just look into the polar scope and put Polaris at that clock position on the big circle. Done. No crazy RA rolls, no "match the Cassiopeia/Big Dipper" orientation". Too dadgum simple, but it's all you need. And you didn't lose your home position rolling the OTA around.

Set the weights down, DEC=90 with whatever method you use to establish your Home/Park position, power cycle to get the HC to make use of the home/Park position, and go forth and align.

#14 chitown

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Posted 21 May 2009 - 09:07 AM

Sorry for being a pain, but please look at my comments below..



1. Set up mount so it points as close as possible to True North in azimuth and your latitude in elevation. Don't worry about home position yet. Leveling the mount does help the whole thing work easier. <<< I use the latitude meter on the side of Atlas and poistion it on "42" as per what i found on google. IS that what you are mentioning?

2. Polaris needs to be on the big circle in the polar scope. All the convoluted instructions on getting the little circle oriented are unnecessary. The hand controller, when the correct date and time are entered, tells you where the little circle should be (the second number in the polar data). <<< moving the RA to match that setting. Hence moving the RA so that polaris matches that data i see on HC? if so, then weight end would go up and scopes down.

2. Either use the hand controller Polaris location, which takes into account the horizontal and vertical flips in the polar scope refractor, or mentally flip the planetarium orientation in both axes. That's where Polaris should appear on the big circle in the polar scope. Piece of cake. Much easier to do than to type up. << Meaning just put polaris on the circle? Without moving the RA? Keeping scopes up and weight end down?


3. So, you set up the mount, you know where Polaris should appear on the big circle from the hand controller or from your planetarium program, just look into the polar scope and put Polaris at that clock position on the big circle. Done. No crazy RA rolls, no "match the Cassiopeia/Big Dipper" orientation". Too dadgum simple, but it's all you need. And you didn't lose your home position rolling the OTA around. <<< Home positions means, again, weights down and scopes up pointing north?



#15 jmasin

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Posted 21 May 2009 - 10:07 AM

Chitown,

No offense intended at all, but I would recommend some time with the user manual, as most of this is defined there. That said -

The polar scope has a few items in the view -
1) the NCP (cross)
2) a large circle representing the track that polaris will follow around the NCP if the mount is aligned.
3) A small circle
4) Big Dipper and Casseopeia

The small circle is merely a helper tool so you can estimate where to put polaris relative to the NCP and Big Dipper/Casseopeia. This small circle IS NOT to be used to dictate where to start the telescope for alignment. It is ONLY to be used to position relative to the constellations.

It is not necessary to use this smaller circle and contort the mount in RA, you can use the larger circle only, this is easier.

For this, you need to know where on the big circle Polaris should be.

Go here: http://astrotips.com...ar_Finder.phtml

Download the program polarfinder. This small program will tell you exactly where on the LARGE circle polaris should be located for any given time (be sure to enter your longitude in the program).

Then, through your polar scope, put Polaris on the large circle in the location dictated by the polarfinder program. At your location, this time of year, ~9PM this will be in the ~1:30 position on the LARGE circle.

You can do all this with power off.

Then, return your scope to HOME position, as dictated in your manual, with power OFF. I.e. loosen clutches and physically move the scope so the counterweight shaft is pointing directly to the ground and the scope is pointing toward the NCP.

The mount assumes you are in this HOME position when you start your alignment (this is outlined in the manual).

#16 chitown

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Posted 21 May 2009 - 10:25 AM


Then, return your scope to HOME position


But I thought that I began with everything in HOME position. All I have to do is match polaris as clock on the big circle?

#17 Skylook123

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Posted 21 May 2009 - 10:35 AM

Sorry, Chitown, I should not have been in a hurry to type and run to work. Your questions are understandable without a bit of experience with the mount. I'll try to clarify.

1. The latitude scale on the side of the Atlas is, charitably, inaccurate. Anecdotally, folks report an error of anywhere from 3 to 7 degrees in the scale. So, even if you were to perfectly level the mount, the odds are that Polaris will be outside the polar scope field of view. Actually, I spent weeks polar aligning on the wrong star, mine was so off. There are two tricks I use to get the latitude close (and remember, the mount needs to be level for the latitude setting to be useful, and BTW the bubble level on the mount is off as well. Sheesh. I use a bulls-eye level on the tripod before adding the mount head). One is to set the dovetail slot to as close to a pseudo north as possible, and use an inclinometer in the dovetail slot. I bought one for a couple of dollars at Home Depot. It's sort of like a big protractor with a pointer that points down, and it's used to measure the angles of walls and shelves. I put the base of the inclinometer in the slot, and adjust the elevation until the protractor reads my latitude. And notice that my latitude indicator on the mount is four and a half degrees off. So, this is a long winded way of saying latitude is good, right latitude is better.

Second method to set latitude is more counter intuitive. It's called an iterative polar alignment. First set the mount up as usual, try to level if possible to keep the settings repeatable. Next, start up the mount an enter all the values. Do a 1-star alignment. Might be many, many degrees off, but that's OK, we'll fix that. Next GOTO Polaris. Notice how far off you are! Take out only half or a bit more of the offset with the azimuth and latitude mechanical adjustments on the mount. Do another 1-star to the same star. GOTO Polaris. Take out 1/2 or a bit more again (never take all of the offset out at one time; your axis error has a sign and you could force it to get worse; only ever take out 1/2 to 3/4 of the error with the mechanicals). Iterate this way (i-star align,then GOTO Polaris) until the errors are very small. Viola. You have your latitude. And terminal boredom, probably.

2. NO NO NO. Don't ttouch the RA; leave the mount set up like the Orion catalogue picture. CW down, OTA roughly pointing North. All you want to do is use the azimuth and latitude mechanicals to put Polaris in the correct clock position on the BIG circle. Ignore the little circle and the pretty constellation pictures; not necessary. Oh, here's a hint; if you use the 1-star iterative method above, eventually Polaris will be in the FOV of the polar scope and you can finish by now adjusting the mechanicals until Polars is on the big circle where it needs to be. Actually, if now you were to roll in RA, Polaris should be always on the big circle. THAT'S Polar aligned! But don't do that; why spoil Home/Park if you have it already.

2. Man, my counting is off; hope the IRS doesn't notice! Anyway, YES YES YES, By Golly, That's It!!

3. Correct again. Remember the inclinometer? I fool around with either that, or the bubble level, on the CW shaft to get the shaft perfectly level. Lock the RA setting circle. Move the CS shaft down until exactly 6 hours RA from when it was horizontal. That's the magic spot. To get the DEC=90 is a bit trickier, but here's a way that works. While you are getting the CW shaft level, once you've got it level, lock the RA clutch and leave it level for a moment or two. Go to the OTA (assumes you have the mount fully set up; actually, this finding the home position is a companion process to do right after you balance the scope). With the CW shaft perfectly level, loosen the DEC clutch and use the inclinometer or bubble level on the side of the OTA and make that level. Set the DEC setting circle to your latitude such that, when you roll it back upright, the DEC numbers will decrease to 0 when you are straight north. Now, when you roll the CW down to the point of 6 hours RA from where it was level, adjust in DEC until it reads 0. Hint: some folks will set the DEC = 0 when it's leveled, then adjust it to the latitude when the CWs are down. Easier to remember. Also, note that in this case the DEC values are meaningless astronomically; you're using the setting circles as fancy protractors, just to get the angles.

If you do the above level the mount, then get the Home position nailed down, then start the polar alignment using a 1-star alignment, setting Polaris on the big circle at the hand controller's value for the clock position, you'll be the Synta alignment expert and can sell your services at star parties. And really, since all of my setups are remote desert or school locations, it only takes me 20 minutes for the full process of adjusting for the latitude, finding Home, and polar and stellar alignment.

Good Luck!

#18 Skylook123

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Posted 21 May 2009 - 10:42 AM

Jon's instructions are of course correct; I just use the hand controller polar value, or just use my planetarium Polaris position and flip it in both axes to get the "sight picture" I should have in the polar scope.

#19 chitown

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Posted 21 May 2009 - 11:00 AM

Please correct me if I am wrong.

This is what I have understood from all the help above:

Steps:
1. Start with the mount facing north in Home position
2. Home position is weight end down, scopes facing north straight
3. All levers locked (RA and Dec)
4. By looking at either the polarfinder software or the clock value on the HC, match the polaris on the BIG cirlce of the polar scope. Ignoring the pictures on it and the polaris small circle
5. Adjust the position of my ENTIRE rig to match polaris on the big circle. WITHOUT touching the RA.
6. Once its in the right position, turn on mount. And start with 1 Star alingment. And select Polaris as GOTO
7. Adjust again if necessary
8. Begin with the rest of the 3 Star Alignment

Please correct me if I am wrong in the most simplest words.

Thanks

#20 jmasin

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Posted 21 May 2009 - 01:56 PM

Chitown,

You basically have it. You may not need to do steps 6 & 7 if you are able to get it good with the polar scope to start.

Clear skies!

#21 rdegoutier

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Posted 21 May 2009 - 02:11 PM

The only thing is that you won't be able to see Polaris when the scope is in the Home position. There is a shaft inside the mount with a hole in it, and the scope has to be horizontal for the hole to line up with the Polar Scope. So change step 1 to:

1. Start with the mount facing north in HORIZONTAL position. Once polar aligned, swing the scope vertical to Home position, put the caps on the Polar Scope, turn the mount on and start star alignment.

#22 Skylook123

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Posted 21 May 2009 - 04:14 PM

Please correct me if I am wrong.

This is what I have understood from all the help above:

Steps:
1. Start with the mount facing north in Home position
2. Home position is weight end down, scopes facing north straight
3. All levers locked (RA and Dec)
4. By looking at either the polarfinder software or the clock value on the HC, match the polaris on the BIG cirlce of the polar scope. Ignoring the pictures on it and the polaris small circle
5. Adjust the position of my ENTIRE rig to match polaris on the big circle. WITHOUT touching the RA.
6. Once its in the right position, turn on mount. And start with 1 Star alingment. And select Polaris as GOTO
7. Adjust again if necessary
8. Begin with the rest of the 3 Star Alignment

Please correct me if I am wrong in the most simplest words.

Thanks


<big grin> OK, I'll cut down the rambling. Sort of correct, except 6 and 7 go ahead of 4 and 5; it's that iteration that will bring Polaris into the polar scope field of view. Then you can put Polaris on the big circle in the right place.

But, as pointed out above, if the mount is in the usual delivered condition, the polar scope opening will be blocked when the OTA is pointing north so first, loosen the three allen screws and make the scope point north when the hole is open. I did mine three years ago and forgot that part.

If you get your routine down, if you are level, and get Polaris onto the big circle where it belongs, and your OTA is square with the mount RA axis, you might only need a 1-star alignment. The point of the 3-star on Synta mounts is to correct for cone error (OTA and RA axis slightly off from each other). If you're "good", a 3-star can make GOTOs less accurate because the hand controller is trying to fix a problem you don't have. If your NCP pointing (polar alignment)is good, and you do a good 1-star, the 1-star provides information for alignment in both axes and that's all you need (but you must be leveled for this to be true). A 2-star will adjust for slight errors in polar alignment and off-level. Three star alignments can give disappointing results for the EQ6/Atlas EQ-G mounts if your mount setup does not have a little cone error.

This is due to the SynScan algorithm; in general, the more stars the better but SynScan tries to fix cone error, so a 3 star might not give you the results you're after. Be very rigorous in your setup (level, polar aligned, good home position), and try a 1-star, then 2-star, then 3-star and see how the GOTOs do. You might be surprised that a 1-star ain't bad when the mount is level and polar aligned.

#23 David Pavlich

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Posted 21 May 2009 - 08:40 PM


Step 3: Return the scope to HOME position.


But if i do this, then polaris will escape the reticle circle of the polar axis scope?


Yes, it does, but that's ok. The exercise to rotate the RA axis to match the sky then putting Polaris in the circle is to polar align the mount and that's it. So unless you move the mount's legs or loosen the Alt or Az bolts, you'll be fairly close to a polar alignment. It will aid in your gotos to be a bit more accurate.

David

#24 Charlie Hein

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Posted 22 May 2009 - 08:38 PM

chitown: stick with Skylook123 for a bit and let's see if you can get this down - everyone is trying so very hard to be helpful but it seems you may be getting confused at all the input... I think that you're just about there!

#25 John Miele

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Posted 23 May 2009 - 12:53 PM

...try a 1-star, then 2-star, then 3-star and see how the GOTOs do. You might be surprised that a 1-star ain't bad when the mount is level and polar aligned.


I can attest to the accuracy of the 1 star alignment. I was lazy one night and started doing a 1 star alignment instead of 3. I have had the best pointing accuracy yet using just the 1 star! Now I level my mount and I do a good polar alignment. And I also use a reticle EP to center my alignment stars. The other night, I was imaging with a DSI II at a focal length of about 700mm. Every target landed on the chip. 1 star aligning is now all I ever use.

John






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