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Celestron Nexstar vs Skywatcher Synscan GOTO pointing accuracy

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#26 Moromete

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Posted 05 July 2013 - 12:17 PM

I owned and tested both the CGEM and Atlas mount side by side. I still have the CGEM. I found that the accuracy of the CGEM with a 2+2 alignment was dead on accurate, while the 3 star alignment with the Atlas was within the field of view of a wide field eyepiece, meaning it was not quite as accurate. One of the big issues for me though was that the CGEM offered more alignment star choices than the Atlas. This can be a issue if you have a lot of trees or obstructions in your observing area like I do. There were a few times when I could not find three alignment stars with the Atlas.

Patrick


@Patrick thx for your valuable feedback. Seems logical what you said and I know Celestron software is better.

What keeps me away from CGEM unfortunately is its weight, cogging issue and DEC issue which is hardware related. Otherwise Celestron software attracts me more than Skywatcher.

Without beeing able to compare Celestron and Skywatcher mounts I feel that software difference in respect of GOTO resides in polar alignment. I feel that Skywatcher needs much better polar alignment for precise GOTO and Celestron is much more forgiving because its software computes better human error in this process due to different math formulas and more callibration stars. When coming down to photography I suppose both mounts need almost as accurate polar alignment for longer exposure and maybe in this case the software difference fades away.
Still this difference in computing precision could be important when ASPA because Skywatcher I think can not compute as well Celestron the polar alignment error and maybe it needs more itterations to reach Celestron's precision. Am I thinking correctly?

Patrick, how scrupulous were you with polar alignment with Skywatcher when you said the object was to the border of the FOV and scope and eyepiece have you been using?

I generally put Polaris in the middle of the polar scope with CG5-GT and I do 2+2 star alignment.

@Uncle Rod maybe I have too much expectations from AZ mode but I was thinking at 1-2 minutes exposures with C11 at F/3 for video astronomy. For photograhpy I would be using EQ mode only with C11 at F/6 on AZ-EQ6 for exposures of up to 5 minutes guided. Am I still crazy?

#27 Moromete

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Posted 06 July 2013 - 07:48 AM

The following 2 questions refer only to Skywatcher Synscan hand controller with the latest firmware 3.35 and not EQMOD software.

If you perform a Pointing Accuracy Enhancement (PAE) on 3 stars AFTER doing a 3 star alignment with EQ6 hand controller, is this similar to Celestron 2+4 star alignment and give the same GOTO accuracy with EQ6 mount or not?

Keeping the same idea and the same procedure described above, will ASPA with EQ6 give the same polar alignment precission as with ASPA on Celestron CG5GT/CGEM or not?

#28 rmollise

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Posted 06 July 2013 - 08:54 AM

Without beeing able to compare Celestron and Skywatcher mounts I feel that software difference in respect of GOTO resides in polar alignment. I feel that Skywatcher needs much better polar alignment...


The SynScan software now has exactly the same polar alignment routine as the NexStar branded scopes. "AllStar," IOW. The go-to alignment process is also considerably more automated with respect to good alignment stars, now. Frankly, I find the SynScan go-to accuracy and the NexStar pretty much the same, now.

Synta/Celestron has also released beta firmware that appears to eliminate the cogging problem (which never affected all users).

#29 rmollise

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Posted 06 July 2013 - 08:56 AM

The PAE can work, but I never use it. It's like Sync, will throw your go-tos off in different parts of the sky, and, frankly, is not needed if you do a good go-to alignment.

The polar alignment routine in the SynScan version doesn't seem any different from in the NexStar branded HCs.

#30 Mike X.

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Posted 06 July 2013 - 09:41 AM

It has a small difference in the steps to follow only.I guess in the performance must be pretty much the same.
The main difference is that in the Synscan version the HC asks to center the star in 2 different steps.One only in Altitude and one only in Azimuth.But that's about it. ;)

#31 Moromete

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Posted 06 July 2013 - 11:26 AM

I suppose Skywatcher makes calculations GOTO the same as Celestron software because ASPA is done the same and you have to use Up and Right arrows when doing final alignment on a star. Even AZ-EQ6 hand controller is presented now to have a database of 42000 like Celestron.
There should be some legal difficulties probably or management decision which prevent using a 100% Nexstar software on a Skywatcher mount but the GOTO calculations done in software seem to be the same.

I'm waitting to see 2+4 star alignment and CPC Auto 2 Star alignment on AZ-EQ6. I think it's a matter of time.

#32 Mike X.

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Posted 06 July 2013 - 06:28 PM

I'm guessing that it has to do with the fact that they use 2 entire different ways to make the gotos that make the 2 protocols incompatible.
Synscan counts steps to reach a position, while the nexstar uses the encoders on the motors to reach the desired position.
For implementing nexstar on a SW mount I'm only guessing that the motors should at least have encoders...but again never say never.

For sure both protocols are keep evolving in parallel so..who knows...maybe in the future Synta could come up with a different alignment method for SW mounts...but still..this one is pretty good..I doubt they would do it anytime soon.
I was in love with my celestron mount and I had similar doubts regarding accuracy but I confess to you that the synscan is equivalent to the nexstar regarding this matter.
It is less user friendly than nexstar that's true but it is accurate virtually as the nexstar.

#33 rmollise

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Posted 07 July 2013 - 08:10 AM

I suppose Skywatcher makes calculations GOTO the same as Celestron software because ASPA is done the same and you have to use Up and Right arrows when doing final alignment on a star. Even AZ-EQ6 hand controller is presented now to have a database of 42000 like Celestron.
There should be some legal difficulties probably


There are no legal difficulties. Synta owns both systems. It is the parent company of Celestron AND SkyWatcher. The problem is that the mounts are so different:

Celestron = servo motors and encoders.

SynScan = stepper motors and no encoders. ;)

#34 rmollise

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Posted 07 July 2013 - 08:12 AM

I was in love with my celestron mount and I had similar doubts regarding accuracy but I confess to you that the synscan is equivalent to the nexstar regarding this matter.
It is less user friendly than nexstar that's true but it is accurate virtually as the nexstar.


Exactly. I do note that later releases of the SynScan software seem to be less user unfriendly than the old ones, though. ;)

#35 Moromete

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Posted 08 July 2013 - 05:11 AM

The PAE can work, but I never use it. It's like Sync, will throw your go-tos off in different parts of the sky, and, frankly, is not needed if you do a good go-to alignment.

The polar alignment routine in the SynScan version doesn't seem any different from in the NexStar branded HCs.


According to the Skywatcher Synscan manual: "The pointing accuracy enhancement (PAE) function enables the telescope mount to obtain enhanced pointing accuracy in specific small areas.
After a 1-star, 2-Star or 3-star alignment, the telescope mount might still have a small pointing error due to many factors, such as the flexure of the telescope, atmospheric refraction or other mechanical issues. The amount of pointing error might vary in different portions of the sky.
The SynScan hand control divides the sky into 85 small zones, and users can calibrate the pointing error for each of these zones. The next time that the SynScan controller tries to locate an object in the calibrated zone (or a zone nearby), it will automatically apply the recorded calibration data to compensate the pointing error.
This function is useful for locating faint deep sky objects, and it is also helpful to obtain consistent pointing accuracy for a permanent observatory."


I don't know if I'm reading correctly but the Skywatcher PAE hand controller function doesn't seem to have the same effect like Celestron's Sync after which you have Unsync because, as you said Rod, the GGOTOs will be worse in other parts of the sky than the synced one.

Theoretically PAE should not degrade GOTOs in some parts of the sky because it needs no Unsync, is applied automatically during GOTOs and models the sky better after every added star to it. Seems similar to N-Point function from EQMOD.

Has anyone experience with Skywatcher GOTOs and ASPA after doing PAE on a few stars?

#36 rmollise

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Posted 08 July 2013 - 09:19 AM

I've used this function a time or two. I can tell you rat-cheer that PAE in one are of the sky will throw off accuracy in another.

#37 HowardK

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Posted 08 July 2013 - 04:29 PM

I've used this function a time or two. I can tell you rat-cheer that PAE in one are of the sky will throw off accuracy in another.


So Rod
U reckon its worthwhile using PAE?
Or does it mean that once u have used it in one part of the sky u have to keep using it in all others?

#38 rmollise

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Posted 08 July 2013 - 05:03 PM

I don't think it's worthwhile in most circumstances. It's better just to do a good alignment. A decent polar alignment with the polar scope and a 3-star using the guidance found in the manual, and the mount will put anything I request from horizon to horizon on the chip of My Mallincam Xtreme; that is good enough for me.

#39 Moromete

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Posted 09 July 2013 - 08:49 AM

I've used this function a time or two. I can tell you rat-cheer that PAE in one are of the sky will throw off accuracy in another.


If that's the case in practice than you have been right saying Skywatcher PAE is like Celestron Sync function. Thx for sharing your opinion and test results.


In respect of Celestron ASPA, after reading CG5-GT website support page and CGEM DX manual (newer) I discovered something very interesting regadring the number of callibration stars needed before doing ASPA.
According to point 18 of CG5-GT support page before doing ASPA you need to align on 2+1(or more) callibration stars. http://www.celestron...owledgebase&...
According to point 39 of CG5-GT support page before doing ASPA you need to align on 2+2 callibration stars. http://www.celestron...owledgebase&...
According to page 29 of AVX mount manual before doing ASPA you need to align on 2+1 (or more) callibration stars: "Before using the Polar Align feature, the scope must first be roughly pointed towards north and should be aligned with three stars in the sky. See the “Latitude Scale” section for help with finding north and adjusting the mounts latitude. Once your telescope is aligned on two stars and at least one additional calibration star, slew the telescope to any bright star in its Named Star database list."

According to CGEM manual before doing ASPA you need to align on 2+1 (or more) callibration stars.

In conclusion, for doing an useful ASPA Celestron needs a 2+1 star alignment, more callibration stars giving higher precision.

Considering many people say that 2 star aling is much better than 3 stars alignment with Skywatcher mounts for accurate GOTOs, I wonder how efficient is ASPA with Skywatcher mounts after doing only a 2 star alignment without any callibration star like Celestron.

#40 Moromete

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Posted 09 July 2013 - 09:02 AM

I don't think it's worthwhile in most circumstances. It's better just to do a good alignment. A decent polar alignment with the polar scope and a 3-star using the guidance found in the manual, and the mount will put anything I request from horizon to horizon on the chip of My Mallincam Xtreme; that is good enough for me.


If your EQ6 puts DSO on Mallincam's chip when using a C11 at F/3.3, than EQ6 GOTO's are OK with me too.

It seems you have no problems with 3 star alignment with EQ6 like other users do and you prefer this method to 2 star alignment. This sounds reassuring to me.

But what do you mean by "decent polar alignment"?

Rod, how long are your exposures in general with Mallincam + C11 + Meade 0.33x reducer?

In wonder if instead of buying a AZ-EQ6, my CG5-GT with C11 reduced at F/3 and a Mallincam like camera will be good enough for up to 60s exposures without star trailing.

#41 rmollise

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Posted 09 July 2013 - 09:23 AM

If your EQ6 puts DSO on Mallincam's chip when using a C11 at F/3.3, than EQ6 GOTO's are OK with me too.

It seems you have no problems with 3 star alignment with EQ6 like other users do and you prefer this method to 2 star alignment. This sounds reassuring to me.

But what do you mean by "decent polar alignment"?

Rod, how long are your exposures in general with Mallincam + C11 + Meade 0.33x reducer?

In wonder if instead of buying a AZ-EQ6, my CG5-GT with C11 reduced at F/3 and a Mallincam like camera will be good enough for up to 60s exposures without star trailing.


If your OTA is not completely orthogonal with the mount--which it probably won't be with an SCT--the 3-star makes a difference, since it take cone alignment error into account.

The secrets to the 3-star, as with the 2-star, are in the manual.

--The first two stars should be separated by 3 hours of right ascension if possible. That is more important than their separation in azimuth.

--Star 3 should be between Declination 30 and 70, north or south.

By "decent," I mean a reasonably careful alignment with the mount's polar scope, at least. I use the hour angle display on the HC to set the position where Polaris goes on the reticle.

My exposures with the Xtreme are generally between 14 and 30 seconds. I can go longer and still get nice stars, but I usually don't need to go longer, and going much more than a minute at my local observing site makes skyglow a problem.

#42 HowardK

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Posted 09 July 2013 - 12:11 PM

Thanks Rod

#43 Moromete

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Posted 10 July 2013 - 03:35 AM

If you only go up to 30s exposure with Mallincam at F/3.3 I suppose you have Gain On an it's set to a higher level.

Regarding your EQ6 practical experience and considering a decent polar alignment beeing done and the lack of Precision GOTO function in Skywatcher handcontroller, what do you do if in the first part of your observing sesion you go only visual with good GOTOs (objects in eyepiece FOV at ~100x) and than in the 2nd part you start using Mallincam and only some DSOs don't land on chip at all in some parts of the sky?

For this situation I suppose Celestron designed Precise GOTO function (which doesn't affect all sky alignment and GOTO pointing accuracy like Sync function does), but if Skywatcher lacks it what can we do to center faint DSOs on small video chips?

#44 Moromete

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Posted 10 July 2013 - 03:48 AM

Just another thing. I think you can use Precise GOTO with Celestron CPC scopes in AZ mode for 30s exposures with a Mallincam for better GOTOs and centering DSOs on Mallincam's chip. What can we do if we don't have Precise GOTO with AZ-EQ6 and we want to use it in AZ mode with Mallincam at 20-30s exposure but DSOs don't land on chip at all?

As a side, I have read that at this moment the GOTOs with AZ-EQ6 in AZ mode are not good, besides the cord wrap problem. Can a user of this mount confirm or infirm this?

#45 johnpd

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Posted 10 July 2013 - 04:45 AM

Just another thing. I think you can use Precise GOTO with Celestron CPC scopes in AZ mode for 30s exposures with a Mallincam for better GOTOs and centering DSOs on Mallincam's chip. What can we do if we don't have Precise GOTO with AZ-EQ6 and we want to use it in AZ mode with Mallincam at 20-30s exposure but DSOs don't land on chip at all?

As a side, I have read that at this moment the GOTOs with AZ-EQ6 in AZ mode are not good, besides the cord wrap problem. Can a user of this mount confirm or infirm this?


Moromete,

I think it was said that the Synta PAE is the same as the Celestron Precise GoTo although I find the Synta manual a little confusing as to what the procedure is. Celestron's is pretty clear. Select an object while in Precise GoTo mode and it gives you a nearby star to align on first. Synta's manual talks about a "reference object" to align on but does not say at what point you select the actual object you want to view.

I have submitted data to my dealer on both the pointing issue and the the cord-wrap issue. A couple of others have mentioned a similar pointing issue in EQ Mode. Hopefully Synta will resolve those shortly. They are supposedly already working on the pointing issue.

JohnD

#46 Moromete

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Posted 10 July 2013 - 05:00 AM

John, as Rod said, Synta PAE is like Celestron Sync and not like Celestron Precise GOTO which doesn't alter the pointing to other parts of the sky than the one were Precise GOTO was calculated.

Celestron Sync is targeting GOTO accuracy to a small part of the sky but affects negativelly than the GOTO to other parts of sky. In contrast Celestron Precise GOTO is targeting GOTO accuracy related to just a single DSO and not a little part of the sky like Sync does and because of this Precise GOTO doesn't affect the pointing on other parts of the sky. At least that's what I understood.

#47 rmollise

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Posted 10 July 2013 - 07:50 AM

If you only go up to 30s exposure with Mallincam at F/3.3 I suppose you have Gain On an it's set to a higher level.

Regarding your EQ6 practical experience and considering a decent polar alignment beeing done and the lack of Precision GOTO function in Skywatcher handcontroller, what do you do if in the first part of your observing sesion you go only visual with good GOTOs (objects in eyepiece FOV at ~100x) and than in the 2nd part you start using Mallincam and only some DSOs don't land on chip at all in some parts of the sky?

For this situation I suppose Celestron designed Precise GOTO function (which doesn't affect all sky alignment and GOTO pointing accuracy like Sync function does), but if Skywatcher lacks it what can we do to center faint DSOs on small video chips?


I'm not sure what you mean by "gain on". No, I don't have the camera in CCD mode; there's no reason for me to. What's "higher level"? I do have it at "6" which is high for some folks...but that and a 14-second exposure will reveal small 16th magnitude galaxies.

I do either video or visual, not both in one evening. I do a careful alignment either way, and have no trouble with go-to accuracy.

I've don't have to use Precise Go-to with the CG5. It's also very good about putting objects on the Mallincam--if I do a careful alignment. ;)

What can you do? You can do a good go-to alignment, which I've already described, following the guidelines for alignment stars in the manual. If you can't be bothered to do that, yes, your go-to accuracy will suffer.

#48 Moromete

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Posted 11 July 2013 - 01:29 AM

Ok, it's clear now.

You wrote on your blog that in practice with the new All-Star polar alignment procedure from Celestron we don't have to re-align the mount again after it like in the past (I didn't know it's possible to re-alignment, to be honest, and now I'm suddenly more happy with my CG5-GT :grin:).

In your experience, is the same thing possible with EQ6 (firmware 3.35) and Skywatcher's software Polar Align procedure or we need to re-align the mount to have good GOTOs?

#49 rmollise

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Posted 11 July 2013 - 08:18 AM

Ok, it's clear now.

You wrote on your blog that in practice with the new All-Star polar alignment procedure from Celestron we don't have to re-align the mount again after it like in the past (I didn't know it's possible to re-alignment, to be honest, and now I'm suddenly more happy with my CG5-GT :grin:).

In your experience, is the same thing possible with EQ6 (firmware 3.35) and Skywatcher's software Polar Align procedure or we need to re-align the mount to have good GOTOs?


It SHOULD be...but the caveat is that I have not been able to try the new firmware in the field.

#50 Moromete

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Posted 11 July 2013 - 09:00 AM

I read now in Synscan manual v3.35 that unfortunatelly you must re-align the EQ6 after doing a software polar alignment with the hand controller! :foreheadslap:
Why don't you copy updated Celestron software functions in your mounts Synta?! :confused:

Considering that Synta owns Celestron begining with 2005 and Skywatcher mounts hand controllers don't have implemented yet after so many years functions from Celestron software like Precise GOTO, All-Star Polar Align without re-alignment needed, more than 1 calibrations stars for initial alignment, no anti cord wrap feature for AZ mode and many other things I suppose Celestron developed alien techonology for their mounts which Synta engineers aren't able to understand and copy in Skywatcher mounts hand controllers. Otherwise, if this is management decision than it's a very bad one because if a mount like AZ-EQ6 had Celestron software features I pointed out, it could be a complete and polished package, a superb mount. Unfortunately now AZ-EQ6 seems handicaped because of incomplete software.






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