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Cable connections for autoguiding?

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#1 Xshovelfighter

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Posted 20 September 2017 - 09:20 PM

Sorry if this has been answered somewhere, but I have not found the answer anywhere.  As far as cable connections, what are my options for an autoguiding setup with the Celestron AVX mount and ASI 120mm camera?

 

I am aware that I can connect the mount to the computer via RS-232 to serial (and possibly serial to USB) connection. From here I would then connect the camera to my laptop and everything should be able to talk to each other.

 

However, can I also satisfy all the necessary connections/communications by connecting the laptop to the camera, and then the camera to the "autoguide port" on the AVX.  It seems like there are a few options, but wanted to confirm that both options work!

 

Thanks for the help!

Nathan



#2 ZL4PLM

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Posted 20 September 2017 - 09:45 PM

Nathan

 

forget the autoguider port smile.gif

 

PHD2 connects to the ASI120 - set the camera in the software for the focal length of the guide scope and pixel size (it should be able to 'guess' the pixel size too) -  make sure you can connect the camera ,.. I can't recall installing any drivers in Win 10 but you might need the latest installer off the ZWO site. 

 

Install ASCOM base software and the celestron drivers

 

Choose the Celestron ASCOM interface for the mount in PHD2  on the comms port it creates when you plug in the adapter (if you use one)

 

make sure you click the brain button on PHD2 and set the Focal length of the OTA etc 

 

Hit connect in PHD2 and it should connect camera and mount together

 

start looping

 

Choose a guide star - hit track and way you go

 

I found you  can get away with almost default settings apart from choosing the camera/guidescope/OTA and mount 

 

shout if you get snags .. but it does work that simple smile.gif

 

an awesome bit of software!

 

Cheers

 

Simon 


Edited by ZL4PLM, 20 September 2017 - 09:47 PM.

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#3 mahagen1

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Posted 20 September 2017 - 10:58 PM

I am not sure of the age of your AVX but I recently received mine and it has a mini USB port in the bottom of the hand controller.  You can connect a normal usb cable then to your computer and not need the rs-232 cable.  Secondly, the ASCOM driver for Celestron is a bit finicky.  You typically need to connect to the mount first to the computer.  Then plug in the usb cable for your guide camera.  I have this same issue running both windows 7 and 10.   If you use a powered USB hub, you can connect the mount to it first, then plug in the guide camera as well which allows you to have only one usb cable running back to your computer.


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#4 glend

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Posted 21 September 2017 - 12:29 AM

There are a couple of options, and in one it is not necessary to go to a full computer mount control, your hand controller can be used to get to your target and then you can guide directly with PHD2 once there and a guide star selected. ASCOM platform 6.3 is required, as is the ASI120 driver, but you don't need a mount connection, the oncamera option will use the  port on the camera to plug directly into the mount guide port. When you connect with PHD2 it will show the ZWO camera driver, push Connect on that, and below that line it will show the oncamera option, push that. I have used this setup for six months with my CGX and it works perfectly. 



#5 Xshovelfighter

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Posted 21 September 2017 - 06:47 AM

Thanks guys, so it does sound like I don't have to plug into the bottom of the hand controller to autoguide. Is there any advantage to this connection over connecting to the autoguide port on the amount?
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#6 rmollise

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Posted 21 September 2017 - 08:38 AM

Sorry if this has been answered somewhere, but I have not found the answer anywhere.  As far as cable connections, what are my options for an autoguiding setup with the Celestron AVX mount and ASI 120mm camera?

 

I am aware that I can connect the mount to the computer via RS-232 to serial (and possibly serial to USB) connection. From here I would then connect the camera to my laptop and everything should be able to talk to each other.

 

However, can I also satisfy all the necessary connections/communications by connecting the laptop to the camera, and then the camera to the "autoguide port" on the AVX.  It seems like there are a few options, but wanted to confirm that both options work!

 

Thanks for the help!

Nathan

 

There is no reason to "forget" the auto guider port as one poster advised. 

 

There are two ways to hook up.

 

One using that auto guide port. You connect camera auto guide (out) port to mount auto guide (in) port on mount using the supplied ST-4 cable. In the software you are using, like PHD, you set your guiding method to "on camera." The serial port, ASCOM, etc., etc. are not involved.

 

Or you connect your PC to the AVX hand control's serial port and guide through that port after telling PHD "ASCOM." 

 

Both methods work equally well, but some people find ST-4 simpler to implement, especially if they will be using other software with the mount, like a planetarium program.

 

If you want a more detailed answer, see this:  http://uncle-rods.bl...pe-academy.html


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#7 Stelios

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Posted 21 September 2017 - 11:27 AM

Thanks guys, so it does sound like I don't have to plug into the bottom of the hand controller to autoguide. Is there any advantage to this connection over connecting to the autoguide port on the amount?

Yes, there is.

 

By connecting to the mount directly (what you call "the bottom of the hand controller") you only need to calibrate *ONCE*, and you can calibrate on a star near the intersection of Meridian and Equator, which allows for the best calibration. This calibration is now good *anywhere in the sky*--moreover, PhD2 knows this and will not try to re-calibrate. 

 

If you are using the ST-4 connection, then you need to calibrate near your target, and if that is near the pole, the calibration won't be as good. 

 

Your calibration via direct connection (ASCOM) can also be good across *multiple sessions* as long as the angle of the guide camera with respect to the mount RA/DEC axes does not change. For example, if you mount the guidescope on a fixed position on your OTA and don't move the guide camera between sessions.

 

And there's a minor (but not insignificant) reason--one less cable to drag and potentially snag. To beginners that's unimportant, but as you get better, such things count. 


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#8 CaptG

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Posted 27 January 2018 - 03:46 PM

Have old lx200 and new ag zwo1290mc, could not get track commands to scope unless I used asi st4 ascom for mount with serial usb on s232 to scope, but would not feedback on scope position, then tried on camera in mount, and Meade classic on aux mount and now have PhD scope control with scope position data, which I needed for drift align.


Edited by CaptG, 27 January 2018 - 04:33 PM.


#9 rgsalinger

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Posted 27 January 2018 - 04:18 PM

Having used both ST4 connections and ASCOM guiding in a single night on three occasions for different reasons, I can attest that there is no performance difference between the two.

 

However, one of those occasions happened when my USB/RS232 adapter failed in the middle of the night. I took out the ST4 cable and just re-calibrated. I was off and running using my hand controller as a planetarium. I lost my pointing model but I could still plate solve and find stuff easily. On another occasion, for some unknown reason, I could not get MaximDL to calibrate my guide camera. It kept "losing" the star. I switched back to ST4 and it worked.

 

So, I think it's good that there are two ways to do this and I wouldn't "lose" the cable. There's also the use case of a stand alone guider.  I do think that it's better not to use an extra cable if you can avoid it. It's the same principle as using a hub at the mount rather than hanging 4 long cables off the PC going to various components. It's tidier and less prone to error, and using some guiding packages avoids multiple calibrations. This is not the case when guiding is integrated with pointing as it true in MaximDL and the SKYX.

 

One other thing. Not all ST4 cables are the same. Make sure to always use the one that comes with your particular guide camera or you may find (as I have) that a particular cable just won't work. I've always figured that was because the wiring was somehow different.

 

Rgrds-Ross



#10 CaptG

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Posted 27 January 2018 - 04:40 PM

To get mine to work I have the usb from the ag, usb to canon main camera, and usb serial from laptop to scope, and st4 from ag to mount to ccd port, I can live with the 3 cables to laptop, tried over and over other configs but this is only way I get comm with scope on pointing data and commands from phd2. 



#11 Bill Dean

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Posted 27 January 2018 - 06:01 PM

 

Thanks guys, so it does sound like I don't have to plug into the bottom of the hand controller to autoguide. Is there any advantage to this connection over connecting to the autoguide port on the amount?

Yes, there is.

 

By connecting to the mount directly (what you call "the bottom of the hand controller") you only need to calibrate *ONCE*, and you can calibrate on a star near the intersection of Meridian and Equator, which allows for the best calibration. This calibration is now good *anywhere in the sky*--moreover, PhD2 knows this and will not try to re-calibrate. 

 

If you are using the ST-4 connection, then you need to calibrate near your target, and if that is near the pole, the calibration won't be as good. 

 

Your calibration via direct connection (ASCOM) can also be good across *multiple sessions* as long as the angle of the guide camera with respect to the mount RA/DEC axes does not change. For example, if you mount the guidescope on a fixed position on your OTA and don't move the guide camera between sessions.

 

And there's a minor (but not insignificant) reason--one less cable to drag and potentially snag. To beginners that's unimportant, but as you get better, such things count. 

 

Not sure why you infer the ST-4 connection requires calibration or training near the target unless the autoguiding software is rudimentary, the method used for guide correction is independent of what you attest as the software that sends the guide corrections should account for the declination and which side of the meridian the telescope is pointed. Calibration would be required if the camera orientation were changed without an update of the previous calibration rotation angle but if "known" the calibration is valid allowing the use of instrument rotators.

 

Clear skies,

Bill



#12 Pauls72

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Posted 27 January 2018 - 07:53 PM

As rgsalinger mentioned there are 2 flavors of ST4 cables, a straight through and a crossover.

I've guided both ways (ASCOM and ST4) with no problems and see no difference in performance. Since I'm not on a permanent pier, I calibrate at the start of every session. It only takes a a minute or two.

 

ST4-PinOut5.jpg


Edited by Pauls72, 27 January 2018 - 07:55 PM.

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#13 rgsalinger

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Posted 27 January 2018 - 08:43 PM

Bill -

 

this problem seems to be a pecularity of PHD only. PHD is unaware of the declination of the telescope when doing ST4 guiding, then it cannot adjust the pulses to reflect the declination. Same with side of pier. That's been my understanding for a while. They have DEC correction implemented for ASCOM guiding but not for ST4 guiding. I believe this a legacy of the old days when ST4 connections were the only method availalble. It may have changed recently, best to read the PHD manual. 



#14 Real14

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Posted 27 January 2018 - 09:04 PM

Hi,

 

I recently developed a Solar guider and tested it on a iOptron mount as well as a Losmandy mount.

 

As we know that that crossing the meridian I need to reverse the guidiing commands I found out that my programming for the iOptron mount was correct but when I used the Solar guider om the Losmandy Gemini control system I did not need to switch to PM guiding and so the switching of the RA axis was inverted between iOptron and Losmandy wiring, eg RA+ and RA- were inverted 

 

confused1.gif

 

I thought ST-4 is a standard but seems that it is not ... confused1.gif


Edited by Real14, 27 January 2018 - 09:05 PM.


#15 Bill Dean

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Posted 27 January 2018 - 09:33 PM

Thanks Ross,

 

I assume the acquisition software would handle the vector transformations but I suppose some folks may be using PHD guiding in the most simplistic sense with say a DSLR without a computer. Brings back not-so-fond memories of using a Pictor 201XT autoguider but it did beat staring down a guider port and manually guiding when it worked.

 

Clear skies,

Bill



#16 WadeH237

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Posted 27 January 2018 - 10:23 PM

There is actually a performance difference between ST-4 guiding and guiding through ASCOM.

 

The ST-4 port works similar to a button the on the hand controller.  When the guide software wants to issue a command, it calculates the amount of time that the guide signal needs to be active.  It then starts the guide signal, waits the correct amount of time, and then stops the signal.  If the computer is busy or there's no thread immediately available at the right time, the duration of that guide signal may be longer than it should be.

 

The ASCOM guide commands support sending a single command to move the mount a specific amount.  It is not dependent on the computer timing to start and stop the signal at the precise time.

 

The difference is subtle and unlikely to have a significant impact, but it is there.

 

To me, the biggest reason to guide through ASCOM is that I don't need the extra cable to connect to the ST-4 port.  I only image with a computer, and I'm always connected to the mount, so the ASCOM driver is always available.  The most compelling case for ST-4 guiding is that you can skip the computer.  For example, you could image with a DSLR and a remote cable release, and then use a standalone guider that uses an ST-4 cable and is not dependent on a computer.



#17 rgsalinger

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Posted 27 January 2018 - 11:56 PM

I can't disagree with the theory that the computer could be too busy to start stop the mount, but I doubt that could ever happen with a modern computer running a modern OS. A USB 2.0 port can run at many megabits per second and I've never seen any of my computers --- going back 8 years now - that struggled in a manner where they might actually not be able to respond to a timer basically instantaneously. I'd be curious to see anything that documents this being a common use case or to hear from people who have this happening..

 

I've also learned the pulse guiding may not actually be implemented as true pulse guiding. I have an Atlas AZ/EQ6 and I control it with EQMOD. The firmware in the mount cannot support true pulse guiding. So the driver transforms the pulse command into what an ST4 cable would send but sends it directly to the mount firmware. I was schooled on this one a while back by someone who put a sniffer on the port! That also may explain why I never noticed any difference one way or the other with that mount, of course.

 

I do agree that there remain some use cases for the ST4 cable and it sure saved my evening when my FTDI (bought from astro-physics) serial/usb converter crapped out 90 miles from home.

I think that to do true pulse guiding the mount's firmware needs to be able to actually process a single command (start, rate, time) and I really wonder how many actually do so.  

 

Rgrds-Ross



#18 Stelios

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Posted 28 January 2018 - 12:19 PM

I've guided both ways. I used to be exclusively ST-4 when I had my CG-5.

 

It's abundantly clear to me that if you are imaging an object near the pole and calibrate there (using PhD2 and ST-4) then your calibration will be inferior to what can be achieved near meridian and equator.

 

But say you are not. Unless you are imaging a single object every night, who wants to be bothered to re-calibrate? As a matter of fact, who wants to calibrate at all when a saved calibration works? 

 

And as for cable failing, the ST-4 cable can fail just as well as the USB/Rs232 (if that's what one uses--most mounts today can handle straight USB). I carry spares for every single cable I use, as I can't afford to lose an imaging session because of a cable. 

 

Yes, it's no big deal in 99% of the cases if you use ST-4 instead of pulse. But when there's a clear (if minor) advantage and zero disadvantages to a method, that should be the method recommended. 



#19 Bill Dean

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Posted 28 January 2018 - 03:50 PM

Hi Stelios,

I may be confused, are your generalized conclusions based solely on PhD Guiding? I have used ST-4, pulse guiding and Direct Guide approaches with a host of mounts and controllers over the last 20 years with several different acquisition programs and aside from stability/feature issues with ASCOM drivers I haven't noted much difference. I currently use Direct Guide for efficiency but otherwise the correction performance under TSX and Maxim DL offers no fundamental difference. I vote for one less cable and about 20 seconds saved for calibration which is done only if I manually rotate the camera angle but it really is no big deal if you use better featured acquisition software.

Clear skies,
Bill

#20 rgsalinger

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Posted 28 January 2018 - 04:31 PM

The ST4 cable is effectively a backup for the USB/RS232 cable that most mounts IN USE today still need. While newer mounts like my paramount are now effectively USB all older mounts are still using the converters. And, since it can be used in a pinch that's one less cable to carry around (and remember to bring with you which I've seen happen too many times). 

 

I think that what Stelios is missing is the the problem he has points out is related to PHD and it's limitations. I think that this forum is mostly SGP users and they SGP leverages a number of third party products. No such limitation exists with regards to the ST4 cable when it comes to the SKYX or MaximDL. I think his point was that if you are imaging near the pole and are FORCED to calibrate there due to PHD's limitations, then you are going to have trouble getting a good calibration.

 

How much it matters given the cosine correction is beside the point I guess. I used ST4 for about 3 years with my CGE mount. One night after getting a new iOptron mount I switched over. Since then I haven't switched back except in emergencies. There's just no telling what happens when you are (as I am) 90 miles from home and you can't connect to the mount!

 

Rgrds-Ross



#21 xiando

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Posted 28 January 2018 - 04:38 PM

I've never even been able to calibrate using PHD2 anywhere near the pole star, let alone get marginal results. PHD just balks and flips me the proverbial finger.


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#22 Bill Dean

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Posted 29 January 2018 - 07:26 PM

Hi Ross,

 

I think you've hit the nail on the head, I understand the limitation of PHD (actually I'm a little surprised by this but I don't use it so I don't really care) and suppose my confusion lies with this as there's no mention of PHD in Nathan's original question. Hopefully he gets up and running in short order.

 

Clear skies,

Bill



#23 WadeH237

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Posted 29 January 2018 - 10:35 PM

I can't disagree with the theory that the computer could be too busy to start stop the mount, but I doubt that could ever happen with a modern computer running a modern OS. A USB 2.0 port can run at many megabits per second and I've never seen any of my computers --- going back 8 years now - that struggled in a manner where they might actually not be able to respond to a timer basically instantaneously. I'd be curious to see anything that documents this being a common use case or to hear from people who have this happening..

It's more complicated than just the speed of the computer.  Depending on how the guide software is written, it is quite possible that the guide commands could suffer delays even when the computer has plenty of CPU cycles available.  Without getting too technical, I have done performance analysis and low level code optimization on ridiculously fast computers (think hundreds of CPUs) and seen plenty of situations where a particular thread can be stalled even with the computer is near idle.

 

That said, I am in full agreement that this is not something that you are likely to encounter as a problem.  That's why I mentioned that it's subtle and unlikely to have significant (perhaps I should have said "noticeable") impact.
 

I've also learned the pulse guiding may not actually be implemented as true pulse guiding. I have an Atlas AZ/EQ6 and I control it with EQMOD. The firmware in the mount cannot support true pulse guiding. So the driver transforms the pulse command into what an ST4 cable would send but sends it directly to the mount firmware. I was schooled on this one a while back by someone who put a sniffer on the port! That also may explain why I never noticed any difference one way or the other with that mount, of course.

And this is also true.  Even though ASCOM supports what I described, it is up to both the mount driver and the guide software to take advantage of it.



#24 Bill Dean

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Posted 29 January 2018 - 11:48 PM

Hi Wade,

Interesting topic but I can't get past the fact that USB polling isn't what we expect it to be. It's been a while but the matter was discussed years ago in the context of the low latency AO requirements of the SBIG implementation at the driver level but my recollection is a little fuzzy. We certainly ran into issues with other issues non-astro but were temporal constrained which involved quite a bit of engineering overhead and led down some slippery slopes with respect to Windows and USB protocol. I agree with the overall desire for better control but I can't say that I share your optimism in light of the inherent clock drift sources inherent with what we're presented with what we have at a consumer level. I haven't seen the same as a huge detriment, overall the tools we have at this level seem adequate given the conditions we work under.

Clear skies,
Bill

#25 WadeH237

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Posted 30 January 2018 - 01:20 AM

I guess that I'm a little lost at this point.

 

An assertion was made that there is no performance difference between ST-4 and ASCOM guiding (see post #9).  The assertion is not true and I gave the reasons.  I also said each time that I mentioned it, that it's subtle.

 

In response to a reply, I further clarified that it may not be noticeable and agreed that it's dependent on ASCOM driver and guide software implementation - also true.

 

I admit that I'm being pedantic, but I just wanted to state the facts.

 

I never said anything about USB (IMO, it has lots of problems the way we use it, BTW).  I don't use USB to connect to my mount.  I connect via Ethernet.  My second choice would be RS-232.  I only involve USB if I have no alternative.




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