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Nexus DSC vs Synscan GOTO?


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Hi all,

I'm intrigued by the Nexus DSC system but don't know anything about mounting it or what system I'd need. Wifi not a must-have, unless it cleans up the interface and does away with a control pad. Cost is the main issue.

I was wondering if it was faster to align and more accurate in people's experience than the Synscan system on SW dobsonians? Primarily if I was able to increase accuracy once aligned on an object by pressing a button for a 'secondary' realign to correct for any initial error?

I have a non-GOTO 300p flextube and was wondering if it could be easily converted to push to, and roughly what I would need? Just the Nexus DSC unit, or a whole load of brackets, gears, cables etc plus the DSC unit?

Edit - if I make up azimuth markings for my dob base and get a digital inclinometer, I could almost just as easily replicate Nexus DSC for a tiny fraction of the cost, yes? I'd just get real-time coordinates off Stellarium, etc.

Thanks for any thoughts!

Edited by Ships and Stars
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It’s an excellent system, I’ve used a Nexus on a 16” Sumerian and the Nexus DSC on the AZ100. The Nexus only creates the connection to a phone or tablet to use SkySafari or similar, but that in itself works very well. The DSC can operate as an entirely standalone unit with very comprehensive databases on board, but also creates a WiFi link to a phone in the same way.

I find the DSC excellent if you just want to observe some familiar Messier or NGC objects for instance, but personally I find it easier to find more obscure doubles from SkySafari rather than finding them in the DSC catalogue. I’m sure others find different so it is down to personal preference. No doubt the DSC is very powerful.

Generally you just need encoders fitted which connect to the Nexus/Nexus DSC unit then you are away. AstroDevices are very proactive and would advise with what you need to fit I’m sure.

You can align on stars as you go to refine the accuracy although I believe it only uses the last two stars. I have found the accuracy to be excellent; trawling around the Virgo Cluster of galaxies with the 16” was fantastic, no problems identifying which galaxy I was looking at, just check the screen and there it was!

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2 hours ago, omo said:

to get an idea of what you may need, this should help, although its not for the skywatcher the GSO dob should be similar:

https://www.astrodevices.com/resources/GSO/GSO-Encoder-Installation.pdf

 

2 hours ago, Stu said:

I have found the accuracy to be excellent; trawling around the Virgo Cluster of galaxies with the 16” was fantastic, no problems identifying which galaxy I was looking at, just check the screen and there it was!

Thank you omo and Stu! I'm very intrigued by this, if it can pinpoint galaxies then that's exactly what I'm looking for. The Synscan on the 500p can be excellent 'if' aligned and balanced, but if it's a little off at the beginning, this has a substantial knock on effect.

The 300p with Nexus would be a brilliant mid-range scope, I'll contact AstroDevices and see what they say.

Thanks again 👍

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It is a great system with a few minor flaws. Serge (the owner) is top shelf. Multiple times I have emailed a support question and within an hour he has called me from Oz to help! Can't beat that with a sack of cats! I used mine on my two Dob's as well as my old Losmandy AZ8 and currently on my DM6. It is much faster than a GOTO EQ mount in terms of alignment.

The main flaw I have with it is getting updates or observing lists on it. You have to eject the mini flash drive on it, take it to the computer, upload what you need/want, then put it back in. If he had a way to do all that via the wifi then it would be all that and a bag of crisps. But this is a minor nit. It is overall a marvelous system.

Accuracy can be adjusted after alignment via the Sync option. It increases pointing accuracy in the neighborhood of the object you are Syncing on. 

Alignment compared to the SynScan is about the same. 

If you want a good amount of detail on the system here is the manual: https://www.astrodevices.com/resources/NexusDSCreleases/Nexus_DSC_User_manual_2.7.pdf

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8 hours ago, Dr Strange said:

It is a great system with a few minor flaws. Serge (the owner) is top shelf. Multiple times I have emailed a support question and within an hour he has called me from Oz to help! Can't beat that with a sack of cats! I used mine on my two Dob's as well as my old Losmandy AZ8 and currently on my DM6. It is much faster than a GOTO EQ mount in terms of alignment.

The main flaw I have with it is getting updates or observing lists on it. You have to eject the mini flash drive on it, take it to the computer, upload what you need/want, then put it back in. If he had a way to do all that via the wifi then it would be all that and a bag of crisps. But this is a minor nit. It is overall a marvelous system.

Accuracy can be adjusted after alignment via the Sync option. It increases pointing accuracy in the neighborhood of the object you are Syncing on. 

Alignment compared to the SynScan is about the same. 

If you want a good amount of detail on the system here is the manual: https://www.astrodevices.com/resources/NexusDSCreleases/Nexus_DSC_User_manual_2.7.pdf

Thanks very much. Lots of good information here. That is indeed excellent customer service all the way from Australia! The pointing accuracy adjustments are a big one for me as I often wonder if I'm actually in the right place for faint objects and especially galaxies unless it's an obvious one. It's hitting a balmy 17C here today in Scotland, must make the most of summer 🤣

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I use a Nexus DSC with my AYO II mount and the very portable Tecnosky Elle mount. The Nexus DSC is a very good system but important to remember that is is not necessarily better or more accurate than a Synscan system. Accuracy is more about the encoders and the efficiency of the mount than the Nexus itself, that is the data going in needs to be good for the Nexus to decode. You can speak to Serge as mentioned and also Gary Kopff at Wildcard who is extremely knowledgeable. (Also in Oz)  It is worth getting the best encoders you can afford as they are certainly not all equal, better quality lower count encoders can be far more accurate than higher count encoders of less quality. I am sure both Serge and Gary have a system for the mount you have. 

Although I like the the Nexus DSC there a few things to consider. If you want to control your dob with Sky Safari then you do not need the full blown DSC unit. Just get the WiFi Nexus box. There seems little point in having the full unit and then connecting a phone or tablet to it, it just makes it a very expensive WiFi box! Using the DSC stand alone can be very liberating as it is a one stop solution and one that can be customised to your hearts content. The GPS facility is useful if you are going to many different locations, the rechargeable internal battery has a very good standby and usage time, and the display is very clear and modern. The last firmware update also added a 1 star align although I have yet to test it. Two star works as well as anything else I have used based on decent encoders I know are not slipping! Accuracy can be improved using various commands in the system or even the MPOINT analysis feature.  I think there is enough in there to keep you occupied. You can download the manual from the web site https://www.astrodevices.com/Support/ManualsandGuides/index.html

Things I am not so keen on, the keyboard is small and wearing gloves in the Winter makes it very difficult to dial anything in. This is where the Argo Navis wins hands down due to the big scrollable wheel. The menu system is not altogether intuitive enough at times, I think like most the way an arrow points on the keypad should be the direction of travel in the menus, but in the DSC it is not like that and can mean it gets a bit fiddly to find what you are looking for jumping between menus. If you use it enough you will probably get used to it. If you get one ensure you mount it solidly, the units feel a bit fragile and will probably not survive a drop onto concrete, also ensure cabling is neat and tidy without any stressing when you use the mount, easy to damage the encoder port. 

The thing about all this is that this manual push to system is generally more expensive than a full GOTO with the perceived outlook that it does less for you. However it does mean observing in relative silence,  it does give you a lot more direction about catalogues and how you choose to set up a session. It cuts down the issue off power requirements and once set up feels like there is a lot less than can go wrong. The overall user experience of using a Nexus or an Argo is one of a lot more control and a faster way of finding targets than waiting for a GOTO to slew around. So in essence it will appeal to some but not others it is neither better or worse than GOTO, its just another way of finding what you want to see. 

Good luck on your choice and keep us updated!

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11 hours ago, Ships and Stars said:

Thanks very much. Lots of good information here. That is indeed excellent customer service all the way from Australia! The pointing accuracy adjustments are a big one for me as I often wonder if I'm actually in the right place for faint objects and especially galaxies unless it's an obvious one. It's hitting a balmy 17C here today in Scotland, must make the most of summer 🤣

Totally understand. Wow shorts and tee shirt weather for Scotland! ;) Depending on the Dob, Serge may have an encoder kit that will work for you or have one he can modify to fit your dob. I just upgraded my DM6 4,096 tic encoders to his 311K ones. Much better accuracy that way. In addition the algorithm that he uses for alignment is pretty straight forward. It generates a "Warp" factor that is an indicator of how good your alignment is. The lower the number the better. I would suggest using a 12mm illuminated reticle eyepiece to get it as close as possible to the alignment star. In addition the Mpoint alignment function will actually do better for you than the Sync function. Mpoint information starts on page 15 of the manual.

In addition I am attaching the algorithm that pretty much everyone uses for alignment. It is by a Mr. Taki who wrote it up for S&T many years ago. For example Celestron uses 2 alignment stars then 1-4 calibration stars. The calibration stars are like a short Mpoint run. Skywatcher also uses a two star alignment. This is my supposition as I have not confirmed with either Skywatcher or Celestron that this is what they are doing but logic tells me that if it walks like a duck, quacks like a duck, and acts like a duck it isn't a chicken. Ergo this is likely the algorithm they use as the base of their system. 

S&T 2-89-Taki.pdf

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14 hours ago, Dr Strange said:

Totally understand. Wow shorts and tee shirt weather for Scotland! ;) Depending on the Dob, Serge may have an encoder kit that will work for you or have one he can modify to fit your dob. I just upgraded my DM6 4,096 tic encoders to his 311K ones. Much better accuracy that way. In addition the algorithm that he uses for alignment is pretty straight forward. It generates a "Warp" factor that is an indicator of how good your alignment is. The lower the number the better. I would suggest using a 12mm illuminated reticle eyepiece to get it as close as possible to the alignment star. In addition the Mpoint alignment function will actually do better for you than the Sync function. Mpoint information starts on page 15 of the manual.

In addition I am attaching the algorithm that pretty much everyone uses for alignment. It is by a Mr. Taki who wrote it up for S&T many years ago. For example Celestron uses 2 alignment stars then 1-4 calibration stars. The calibration stars are like a short Mpoint run. Skywatcher also uses a two star alignment. This is my supposition as I have not confirmed with either Skywatcher or Celestron that this is what they are doing but logic tells me that if it walks like a duck, quacks like a duck, and acts like a duck it isn't a chicken. Ergo this is likely the algorithm they use as the base of their system. 

S&T 2-89-Taki.pdf 357.69 kB · 0 downloads

Ah that's brilliant, thanks very much! I'm hoping to get one more crack at galaxies before we lose total darkness. The pointing accuracy with your setup sounds very good, the synscan isn't bad, but I need to do some fine tuning in backlash. The 300p however would greatly benefit from a good push-tp to system. Fairly warm here again today, but rest of week looking so-so. Thanks again!

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On 10/04/2020 at 04:08, Ships and Stars said:

I was wondering if it was faster to align and more accurate in people's experience than the Synscan system on SW dobsonians? Primarily if I was able to increase accuracy once aligned on an object by pressing a button for a 'secondary' realign to correct for any initial error?

I'm curious why my AZ EQ6 needs to be leveled with the bubble with Synscan but my Sky Commander DSC could care less about being level? the SC can be accurate to 1/10 deg with 10,000 step encoders. I can easily get .25 deg in use with the 24" dob.

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On 11/04/2020 at 10:53, JG777 said:

The overall user experience of using a Nexus or an Argo is one of a lot more control and a faster way of finding targets than waiting for a GOTO to slew around. So in essence it will appeal to some but not others it is neither better or worse than GOTO, its just another way of finding what you want to see. 

Good luck on your choice and keep us updated!

Thanks very much for that, a goldmine of information there. It will be a little while, but I will keep everyone posted.

16 minutes ago, jetstream said:

I'm curious why my AZ EQ6 needs to be leveled with the bubble with Synscan but my Sky Commander DSC could care less about being level? the SC can be accurate to 1/10 deg with 10,000 step encoders. I can easily get .25 deg in use with the 24" dob.

I don't know on that one Gerry, I've heard others comment here or on CN a rough level will suffice for the synscan, but I like to get it as close as possible assuming it does indeed have an effect on pointing accuracy. Good point!

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1 minute ago, Ships and Stars said:

I've heard others comment here or on CN a rough level will suffice for the synscan, but I like to get it as close as possible assuming it does indeed have an effect on pointing accuracy.

One of the reasons the TSA120 is not used much is the mount-its VG but set up is challenging. Levelling the mount and then finishing "up and to the right" is a pain. It is nowhere near as accurate as the SC. I hear Nexus DSC are VG too.

I replaced the SW GPS (member Rainmakers suggestion) with one made in WPG, Man- I don't have to input anything. Once set up to track planets, the AZ EQ6 is amazingly accurate for this.

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1 hour ago, Ships and Stars said:

I do now! 

lol!

Well, they provide enough accuracy- actually more accuracy than typical mounting systems do...IMHO. By mount I also mean what the SCOPE SITS ON.

This is a crucial factor with both tripods and dobs. If the scope moves even a small amount and the encoder does not- wham, off target. Most think tripods are stable and they can be laterally. One little push down on a leg skews things in all directions. A dob on grass is not so stable either.

Then there is mount backlash... this is why we have to take it up by going up and to the right... but- the backlash remains and reveals itself in inaccuracy.

To recap- to improve on 10,000 step encoders everything else has to be perfect, zero scope movement without the encoders following. A mentor explained this to me. A typical dob has excellent encoder tracking- ie the encoder moves with the scope. I had pursued the thought of 40,000 step encoders before a lesson in enlightenment changed my mind and I now try to maximize other things in my control.

A third alignment point is also a huge advantage which used properly mitigates unwanted mount movement to some extent. ie a stable base. Of course these are just my current thoughts, probably wrong :icon_mrgreen:

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19 minutes ago, jetstream said:

A third alignment point is also a huge advantage which used properly mitigates unwanted mount movement to some extent. ie a stable base. Of course these are just my current thoughts, probably wrong :icon_mrgreen:

Thanks, all of this makes sense above. I suppose you could have a highly accurate encoder, but the overall system is only as strong as the weakest link(s), so a few small wobbles here and there with a leg flexing or a base settling into the ground can add up I suppose. 

It stands to reason a three star align would resolve or reduce error effectively, but not sure why manufacturers (that I'm aware of) don't offer it? Presumably it wouldn't be difficult to add a third alignment point, so perhaps it's a case of diminishing returns? I do note there are some tricks in the back of the synscan manual I've yet to try, that could be something to do this summer when the stars are ou, but too bright for most DSOs.

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Just now, Ships and Stars said:

Thanks, all of this makes sense above. I suppose you could have a highly accurate encoder, but the overall system is only as strong as the weakest link(s), so a few small wobbles here and there with a leg flexing or a base settling into the ground can add up I suppose. 

It stands to reason a three star align would resolve or reduce error effectively, but not sure why manufacturers (that I'm aware of) don't offer it? Presumably it wouldn't be difficult to add a third alignment point, so perhaps it's a case of diminishing returns? I do note there are some tricks in the back of the synscan manual I've yet to try, that could be something to do this summer when the stars are ou, but too bright for most DSOs.

Question- what accuracy does you 20" Synscan give?

My 2 dobs both easily find any object in .8deg TFOV and after using the "re align on object" (sort of a 3rd point) the accuracy is down to at least a quarter degree. What I do is re align on an easy object near my target and then the accuracy carries through to the target.

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1 minute ago, jetstream said:

Question- what accuracy does you 20" Synscan give?

My 2 dobs both easily find any object in .8deg TFOV and after using the "re align on object" (sort of a 3rd point) the accuracy is down to at least a quarter degree. What I do is re align on an easy object near my target and then the accuracy carries through to the target.

Generally it lands at least in the outer third of the FOV with a 21E or 20mm APM. I'd have to look up how many degrees fov that gives. When it's off, it's consistently off though! By this I mean sometimes it lands right on something and I think great, but then slews a few degrees away and settles. I'm thinking when it does this it's needing some backlash elimination, but it hasn't happened much lately. I do have a lot of weight added to the base, would like to lose 500-750g there. Overall it's decent, but not pinpoint by any means. It will get you pretty close though. I've been able to find a lot of planetary nebulae, etc fairly easily without knowing what size or how bright they are. It's the really faint galaxies and nebula like the Cocoon that makes me second guess if I'm really right there or not, but suppose that's the nature of some of these objects?

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1 minute ago, Ships and Stars said:

then slews a few degrees away and settles.

Sorry for my ignorance here Robert but your scope is driven? gears or direct?

If so then yes, there must either gears and a brake (motor maybe) or direct with a brake (motor?)

I would try what I do with the AZ EQ6- do your alignment with very narrow FOV eyepieces and slew in the same direction to do so. Then try an object slewing in that same direction again, I'm very curious about the results.

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9 minutes ago, jetstream said:

Sorry for my ignorance here Robert but your scope is driven? gears or direct?

If so then yes, there must either gears and a brake (motor maybe) or direct with a brake (motor?)

I would try what I do with the AZ EQ6- do your alignment with very narrow FOV eyepieces and slew in the same direction to do so. Then try an object slewing in that same direction again, I'm very curious about the results.

Yes it's driven, I tried your suggestion earlier this year and started using an 8mm plossl - this definitely helped tighten things up. I'll only use the up and right keys when centering on a star as per the synscan manual, but never thought to check targets slewing in that same direction if I follow you correctly. Interesting point!

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55 minutes ago, Ships and Stars said:

Yes it's driven, I tried your suggestion earlier this year and started using an 8mm plossl - this definitely helped tighten things up. I'll only use the up and right keys when centering on a star as per the synscan manual, but never thought to check targets slewing in that same direction if I follow you correctly. Interesting point!

Its worth a try Robert, all to gain and nothing to lose. Side note- for an undriven frac or SCT mount I think the Diskmount or possibly the AYO is the way to go, used with encoders and DSC.

The surface its sitting on is crucial too, my best is compacted gravel.

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22 hours ago, jetstream said:

I'm curious why my AZ EQ6 needs to be leveled with the bubble with Synscan but my Sky Commander DSC could care less about being level? the SC can be accurate to 1/10 deg with 10,000 step encoders. I can easily get .25 deg in use with the 24" dob.

It helps with the alignment a bit if the mount is level with the earth. Though I found that to be not quite the case with my AZ-EQ6. I didn't have to be spot on level in alt/az mode. The calculations it makes based on the alignment stars didn't seem to take level into too much account. But I used the mount only for visual in alt/az save for one time in EQ mode to image the blood moon. 

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One nice aspect of the encoders on the AZ100 is that there is no backlash or requirement for ‘up and left’ type positioning when aligning. You just centre the target and align. Very accurate and quick to do.

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