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Atlas GoTo Question

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#1 tclehman1969

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Posted 05 May 2013 - 02:14 AM

Evening!

So, last night I had a chance to get my scope out for an extended time. Sadly, it was not the best of seeing conditions, but I'll take anything!

Anyway, I have moved past the problems I had initially with polar alignment -- it's so easy, don't know how I couldn't get it right to begin with -- but have a question re: GoTo. Last night I did a 3-star alignment. My stars were, in order, Arcturus, Capella, Spica. After running this and each of the stars being way off the mark, not even in my C8 with a 36mm eyepiece, the hand controller came up and said, "Alignment May Be Poor." Yikes!

Sure enough, it was most certainly off. But, since I was looking at getting wide field astro pics, I didn't worry about it too much. After a bit I thought I would like to get some pics of Saturn at prime focus. So, moved my camera down to the C8 and popped my Bhatinov mask on. For focusing, I figured I'd use Arcturus to take my focusing images. Used the hand controller and entered Arcturus. Mount swung over and bang! Arcturus was dead center. I'm guessing because it was an alignment star I used. Anyway, got focused and used the hand controller and entered Saturn. Again, essentially dead on center. Then later used the hand controller and selected M13. Again it was dead on.

So why after star alignment couldn't find anything and then later I get some objects dead on?

Just curious if anyone has some insight on this.

Thanks!

#2 neptun2

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Posted 05 May 2013 - 04:23 AM

Well that's strange. I personally have never seen such message with my heq5 pro (sirius). It is normal the first star to be way off (even out of the field of view of finder scope) but the next 2 stars are always either close to the center of the finder scope or even in the field of view of my dslr (i use it for centering and not eyepiece).

#3 Tapio

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Posted 05 May 2013 - 04:40 AM

My guess is it's because Arcturus was synced and Saturn and M13 (and Arturus) are all same part of the sky.
Maybe Capella or Spica were off.

#4 rmollise

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Posted 05 May 2013 - 07:22 AM

Evening!

So, last night I had a chance to get my scope out for an extended time. Sadly, it was not the best of seeing conditions, but I'll take anything!

Anyway, I have moved past the problems I had initially with polar alignment -- it's so easy, don't know how I couldn't get it right to begin with -- but have a question re: GoTo. Last night I did a 3-star alignment. My stars were, in order, Arcturus, Capella, Spica. After running this and each of the stars being way off the mark, not even in my C8 with a 36mm eyepiece, the hand controller came up and said, "Alignment May Be Poor." Yikes!

Sure enough, it was most certainly off. But, since I was looking at getting wide field astro pics, I didn't worry about it too much. After a bit I thought I would like to get some pics of Saturn at prime focus. So, moved my camera down to the C8 and popped my Bhatinov mask on. For focusing, I figured I'd use Arcturus to take my focusing images. Used the hand controller and entered Arcturus. Mount swung over and bang! Arcturus was dead center. I'm guessing because it was an alignment star I used. Anyway, got focused and used the hand controller and entered Saturn. Again, essentially dead on center. Then later used the hand controller and selected M13. Again it was dead on.

So why after star alignment couldn't find anything and then later I get some objects dead on?

Just curious if anyone has some insight on this.

Thanks!


Go-to accuracy can be different in different parts of the sky, usually due to poor alignment star choices.

The current SynScan firmware does some filtering of the alignment star choices, but it is still up to you to choose good ones. Most important, the first two stars must be separated by 3 - 4 hours of right ascension. Have a look at the manual's tips and use those in accepting alignment stars. If I do that, the C8 will easily put anything in the field from horizon to horizon.

#5 Phil Sherman

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Posted 05 May 2013 - 08:11 AM

Another cause of pointing errors is cone error, where your scope's optical axis isn't aligned with the mount.

The biggest source of alignment error is not being able to correctly set the home position of the mount. The Atlas, when powered up, assumes that the mount is perfectly set in the home position, something that's almost impossible to do. The first GOTO you do assumes perfect polar alignment and home position.

I resolve this by unlocking the clutches and pushing the scope to the first alignment star. Final adjustments are made using the hand controller buttons after relocking the clutches. This procedure aligns the scope to the hand controller's concept of where the first alignment star is located. The other alignment stars are entered as described in the manual.

Assuming that I have a good initial polar alignment, this procedure has always given me goto results that place the target inside the middle 2/3 of a low power eyepiece.

Phil

#6 pjensen

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Posted 05 May 2013 - 08:38 AM


Go-to accuracy can be different in different parts of the sky, usually due to poor alignment star choices.

The current SynScan firmware does some filtering of the alignment star choices, but it is still up to you to choose good ones. Most important, the first two stars must be separated by 3 - 4 hours of right ascension.


Wow, this explains what happened to my GoTo accuracy two nights ago. I got out a bit late so Sirius had already set (usually my first alignment star). The controller offered Castor and Procyon as the first two alignment stars (RA: 7hr 24' and 7hr 39'). So these two star were only 15 minutes apart in RA!! And here I thought the controller was smart... Smart but not smart enough. :)

Thanks,

Paul

#7 tclehman1969

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Posted 05 May 2013 - 11:59 AM

Well that's strange. I personally have never seen such message with my heq5 pro (sirius). It is normal the first star to be way off (even out of the field of view of finder scope) but the next 2 stars are always either close to the center of the finder scope or even in the field of view of my dslr (i use it for centering and not eyepiece).


Yeah, this is the first time I have seen the poor alignment message. Ironic I got the message on a night I was particularly critical with my polar alignment procedures.

#8 tclehman1969

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Posted 05 May 2013 - 12:02 PM

Go-to accuracy can be different in different parts of the sky, usually due to poor alignment star choices.

The current SynScan firmware does some filtering of the alignment star choices, but it is still up to you to choose good ones. Most important, the first two stars must be separated by 3 - 4 hours of right ascension. Have a look at the manual's tips and use those in accepting alignment stars. If I do that, the C8 will easily put anything in the field from horizon to horizon.


Thanks, Rod. Seeing as how my first 2 stars were separated by only 40 mins or so of RA, that could pose a bit of a problem.

#9 tclehman1969

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Posted 05 May 2013 - 12:25 PM

Another cause of pointing errors is cone error, where your scope's optical axis isn't aligned with the mount.

The biggest source of alignment error is not being able to correctly set the home position of the mount. The Atlas, when powered up, assumes that the mount is perfectly set in the home position, something that's almost impossible to do. The first GOTO you do assumes perfect polar alignment and home position.

I resolve this by unlocking the clutches and pushing the scope to the first alignment star. Final adjustments are made using the hand controller buttons after relocking the clutches. This procedure aligns the scope to the hand controller's concept of where the first alignment star is located. The other alignment stars are entered as described in the manual.

Assuming that I have a good initial polar alignment, this procedure has always given me goto results that place the target inside the middle 2/3 of a low power eyepiece.

Phil


I have often wondered about this. When I bought the mount from Orion, I asked how to align the scope with the polar axis and they said it didn't matter, that where the scope is pointing doesn't effect anything and that it would work out. I couldn't figure this out because if the main scope is several degrees off true from the home position, if you select Sirius as your first star, the main scope, if not aligned well, could be pointing at Betelgeuse. Obviously, I am being a little exaggerated with this but just to illustrate. Technically, if I put the polar scope crosshair on Polaris, shouldn't the main scope and your finder scope also be pointed at Polaris?

I have also verified the polar scope is aligned appropriately by pointing at Polaris, setting Polaris on the circle of the reticule and then rotating the RA and the star scribed perfectly with the finders reticule. So, obviously, I don't want to mess with that.

But, coming back to your point, Phil, the method you describe, unlocking the clutches on the first star to get things closer and then fine tune with the controller then move on to stars 2 and 3, was something I wondered about on my way home that night. Sounds like you have had good success with that. I am curious if anyone else has done it this way and had success.

This is a new mount to me and I'll tell you, I am having the best time learning how to use it! I am probably over-analyzing the heck out of it, but I don't care as it gives me something to think about that isn't work related! :jump: And once I am happy with that, then I'll over analyze how to take pictures and such! This is a fun hobby :jump: :grin:

#10 rmollise

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Posted 05 May 2013 - 01:58 PM

Another cause of pointing errors is cone error, where your scope's optical axis isn't aligned with the mount.

The biggest source of alignment error is not being able to correctly set the home position of the mount. The Atlas, when powered up, assumes that the mount is perfectly set in the home position, something that's almost impossible to do. The first GOTO you do assumes perfect polar alignment and home position.

I resolve this by unlocking the clutches and pushing the scope to the first alignment star. Final adjustments are made using the hand controller buttons after relocking the clutches. This procedure aligns the scope to the hand controller's concept of where the first alignment star is located. The other alignment stars are entered as described in the manual.

Assuming that I have a good initial polar alignment, this procedure has always given me goto results that place the target inside the middle 2/3 of a low power eyepiece.

Phil


Home position only affects how close you come to the initial alignment stars, not the final alignment quality.

#11 Skrenlin

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Posted 05 May 2013 - 10:09 PM

Unlocking the clutches was how I've gotten Saturn in the eyepiece a few times before sunset on my orion sirius mount. I set up the mount with polar scope pointed to magnetic north, went through a 1 star alignment, just said ok on whatever the first star it picked was, then did a goto to the moon (these times were during outreach events at/near dusk). Once the mount beeped for GOTO complete, I unlock the clutches, center the moon in a 32mm, redog the clutches, then try a GOTO to Saturn (or Jupiter). If its not in the eyepiece, GOTO back to the moon, do the escape-recenter alignment and try the planet again. I've nailed it a couple times this way. Seeing Saturn against a blue sky is pretty cool, indeed!

#12 johnpd

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Posted 06 May 2013 - 04:52 AM

Go-to accuracy can be different in different parts of the sky, usually due to poor alignment star choices.

The current SynScan firmware does some filtering of the alignment star choices, but it is still up to you to choose good ones. Most important, the first two stars must be separated by 3 - 4 hours of right ascension. Have a look at the manual's tips and use those in accepting alignment stars. If I do that, the C8 will easily put anything in the field from horizon to horizon.


For 2-star alignment in Az-Mode, the manual mentions that the stars should be:

1) between 15 and 60 degrees in altitude with an altitude difference between 10 and 30 degrees.

2) between 45 and 135 degrees difference in azimuth with around 90 degrees as the optimum.

I played a little with an iPhone/iPad app (ALTitude AZimuth ALIGNment) for aligning Alt-Az mounts. It generates a pair of stars which, if you draw a line between them, the line passes as close as possible through the zenith. The further the distance between the two stars the better. It seemed to give pretty good results.

JohnD

#13 jgibson1@emich

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Posted 08 May 2013 - 06:39 PM

I haven't read all the replies above.....

But FWIW, I ALWAYS perform a 1-star alignment with my Atlas EQ-G (after very precise drift polar alignment!!!!). I tend to pick a single star in the east near the celestial equater and at least 30 degrees off the horizon.

The alignment star is almost always WAY off. I manually stop the auto-slew and then manually slew to the selected alignment star. Once centered in my DSLR (attached to my 8" f/4.9 Newt) I hit enter and am off and running.

After this alignment, the mount will place any object in the eastern sky within the center 25% of the DSLR's FOV. If I slew to an object on the western sky then I may find the target within the center ~50-75% of the DSLR's FOV. Since I am imaging this is more than accurate enough for my needs.

To ask more of a "budget" mount is probably not nice ;) IMO. I have been doing this same routine with great success since I bought the mount in 2006!!!

Clear Skies,
Jason

#14 Phil Sherman

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Posted 09 May 2013 - 08:16 PM

When a SYNTA mount/hand controller is powered up, it uses a sky model that includes the following assumptions:
1. The tripod surface is perfectly level
2. The date and time are a perfect match to the actual values.
3. Your location is exactly what you entered.
4. The mount is perfectly polar aligned.
5. You have no cone error between the mount and the scope's optical path.
6. The home position of the scope is perfect.

Items 1-5 are usually set quite accurately. The biggest issue I've run into is the home position. There's no surfaces on the mount that will let you set it perfectly with a level or inclinometer. When you loosen the clutches for ONLY the first alignment star, you're bringing the scope into synchronization with the hand controller's sky model.

When you move the scope with the directional buttons then press the sync button, you are changing the hand controller's sky model to match where the scope is pointing.

Phil

#15 vorkus

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Posted 09 May 2013 - 10:54 PM

I use EQMOD and my mount is on a pier but here's how I establish home. Eyeball the counter weight shaft and the altitude adjustment bolt. I then use my guide camera and guide scope to center polaris. I use a polar align tool that tells me where polaris should be as an offset of dead center and I put it there by adjusting the declination axis. If I do this right, then the first star is in the fov of my guide camera.

#16 rmollise

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Posted 10 May 2013 - 09:59 AM

When a SYNTA mount/hand controller is powered up, it uses a sky model that includes the following assumptions:
1. The tripod surface is perfectly level
2. The date and time are a perfect match to the actual values.
3. Your location is exactly what you entered.
4. The mount is perfectly polar aligned.
5. You have no cone error between the mount and the scope's optical path.
6. The home position of the scope is perfect.



1. This doesn't make any difference.
2. This is important for go-tos to solar system objects, and the alignment stars the HC offers. It does not have to be any more precise than what your watch says.
3. As above. Precision doesn't help much here either.
4. The mount does NOT have to be perfectly polar aligned. The polar scope is more than adequate.
5. If, like most users, you have some cone error, you use a three star alignment, which takes that into account.
6. This doesn't have to be perfect, either. How close you are to home only affects how close you come to the initial alignment stars.

What really matters most? Alignment star choice. Follow the tips in the manual religiously even if you ain't religious. :lol:

#17 Phil Sherman

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Posted 10 May 2013 - 03:42 PM

When a SYNTA mount/hand controller is powered up, it uses a sky model that includes the following assumptions:
1. The tripod surface is perfectly level
2. The date and time are a perfect match to the actual values.
3. Your location is exactly what you entered.
4. The mount is perfectly polar aligned.
5. You have no cone error between the mount and the scope's optical path.
6. The home position of the scope is perfect.



1. This doesn't make any difference.
2. This is important for go-tos to solar system objects, and the alignment stars the HC offers. It does not have to be any more precise than what your watch says.
3. As above. Precision doesn't help much here either.
4. The mount does NOT have to be perfectly polar aligned. The polar scope is more than adequate.
5. If, like most users, you have some cone error, you use a three star alignment, which takes that into account.
6. This doesn't have to be perfect, either. How close you are to home only affects how close you come to the initial alignment stars.

What really matters most? Alignment star choice. Follow the tips in the manual religiously even if you ain't religious. :lol:


We could argue about these points until the end of time and still both be right.

1 - N-S levelling errors will be compensated for with the altitude adjustment when doing polar alignment. E-W levelling errors will NOT be compensated for if you set the home position using alignment marks you added to the mount. If you use a level to set the home position, then, as you said, the tripod doesn't need to be E-W level. If you're planning on doing a drift alignment then a level mount decouples the azimuth and altitude adjustments, making drift alignment a bit easier.

2,3 - Errors between what you entered and the actual values should be less than a few minutes of arc and are not a significant factor in the initial alignment star pointing error. A wide field finder would still have the target in its FOV.

4 - Polar scope alignment should get you within a dozen minutes of perfect polar alignment. With practice, you can do better. Again, this wouldn't be enough to move the initial alignment star out of a finder's FOV.

5 - Cone error could be a couple of degrees which is significant. Hopefully, you've adjusted your scope in its rings to eliminate most of this. As you said, a three star alignment will compensate for it.

6 - If you can look at your mount in the home position and determine that it's 3-5 degrees off vertical then you're a lot better at guestimating a vertical line than I am. When I unlock the clutches for the first alignment star, I'm assuming that the hand controller has pointed the mount to the correct place and that any aiming errors are the sum of all of the individual errors. Pushing the scope to that target zeros out those errors.

We all have to practice setting up our mounts and work out the techniques that work best for ourselves. My setup procedure when I'm planning on imaging for a few days is a lot different than what I use at a star party where the public is clamoring to see something long before the end of astronomical twilight.

I solved my biggest headache, setting the correct time, by keeping a watch, clock, and the timeclock on all of my computers set to GMT. No more DST and no more time zone issues when I travel.

Phil

#18 rmollise

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Posted 10 May 2013 - 05:03 PM

How close you are to home position only determines now close you come to the alignment stars and has zero effect on the quality of the final go-to alignment. I'm not interested in arguing anything. I've been using the mounts for some time now and stand by my statements on every point, however. ;)

#19 Madratter

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Posted 10 May 2013 - 08:41 PM

Apart from the argument about how to best align this mount, I'm interested in the statement Phil made that his gotos end up "inside the middle 2/3 of a low power eyepiece."

I'm used to my CG-5 and gotos tend to be VERY accurate with my mount once aligned. I would say my gotos are usually with 5' of dead center.

Is the Atlas actually that bad? While goto accuracy isn't the only thing, which is why I'm strongly considering the Atlas for AP instead of my CG-5, it sure is nice.

#20 Phil Sherman

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Posted 11 May 2013 - 10:01 AM

Apart from the argument about how to best align this mount, I'm interested in the statement Phil made that his gotos end up "inside the middle 2/3 of a low power eyepiece."

I'm used to my CG-5 and gotos tend to be VERY accurate with my mount once aligned. I would say my gotos are usually with 5' of dead center.

Is the Atlas actually that bad? While goto accuracy isn't the only thing, which is why I'm strongly considering the Atlas for AP instead of my CG-5, it sure is nice.


My statement about pointing accuracy was intended to apply to a rapid setup used for a star party. Imaging is a whole different story. It's my belief that, for AP, You can't beat the Atlas mount for pointing accuracy unless you're willing to move up to the $10k class mounts. If you're using using Pinpoint or AstroTortilla to analyze a star field, any of the GEMs in the lower price range will give perfect pointing.

The Atlas mount, using the hand controller, Is not the best approach for AP. You'll need to use a computer for imaging so you'll also want to run the mount from the computer. The best tool for this is EQASCOM (aka EQMOD). This freely downloadable software, combined with any planetarium program that will drive an ASCOM mount, will give you pointing accuracy that's within a few arcseconds of your target. If you use your mount on a permanent pier, you can save and restore the pointing model from session to session. A well built pointing model automatically handles atmospheric refraction, another bonus. EQMOD will also merge a PEC control file into the mount control, further improving tracking.

As to its accuracy, I imaged comet ISON this past February. I determined its location using S&T's finder chart, pointed the scope using RA and DEC, and imaged away. ISON was just about dead center in the FOV of my T3i images. I located the comet by doing a MAX combine of an hour's images and saw the short trail left by the starlike comet. A second set of images showed the comet's slow journey through the star field starting after the end of the first set.

Guiding the Atlas with EQMOD is very easy to do. I've been using an 80ST as a guidescope with a DSI I Pro camera as the guide camera. PhD runs the DSI and guide signals are fed to the mount using pulse guide which eliminates the need for an ST4 adapter and cable.

I use CdC as my planetarium program. CdC will use many different star catalogs including the Hubble Guide Star (HGS) catalog, which I've installed. Again, CdC is a free download.

I run my mount using different computers. The smallest is an older ASUS Eee with 2G memory and an 800mhz Celeron CPU running WinXP. This underpowered system will run the mount, guide, and capture images without problems. The only thing it won't do is image processing - too little memory and not enough CPU for that. It's a great field use computer because the external power input for it is 12V, allowing a direct connection to a deep cycle battery. My "big" laptop is a Lenovo T410 running Win7 (64 bit) with an Intel I5 CPU. All of the software I use on XP runs on this system and to speed up image processing, I copy images to an external SATA SSD before working on them.

Phil

#21 Madratter

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Posted 11 May 2013 - 12:32 PM

Thanks Phil. That is a very thorough answer and what I was looking for. I had completely forgotten that you can build an elaborate pointing model with EQMOD. I had read that before, but it slipped my mind. That is very reassuring.

I image from my observatory and my mounts are often setup for long periods of time, even though I don't have a pier (my 20" f/5 sometimes gets used from there as well).






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