Celestron Unified Driver 6.1.7350, PHD2, and NexStar 8SE with Wedge

[G-Man 007]

I have a NexStar 8SE Alt/Az Mount but I also plan to use a Wedge to turn the mount into an equatorial mount.  On the StarSense Hand Controller, I plan to select wedge and plan to choose EQ North.  Based on this update, then I presume that in the ASCOM Driver, for CanPulseGuide it should state True.

Currently when I select Celestron Unified Driver 6.1.7350 on my mount before having a wedge for PHD2, PHD2 sends an error indicating "Mount does not support the required pulse interface" but I presume currently, CanPulseGuide in the ASCOM Driver indicates False which should change to True when Wedge and EQ North is selected.

As such, does anyone have experience with this proposal and will PHD2 be able to work with my NexStar 8SE Alt/Az Mount with a Wedge equivalent to a EQ Mount like a Celestron AVX Mount.  I have discussed the matter with Celestron and they indicated that Celestron Unified Driver 6.1.7350 can be used with the Celestron AVX mount which means the driver natively includes pulse guiding.

Look forward to review and response.

Thanks,

Edmund

[Dale Ghent]

It doesn't matter what's in the guts of the ASCOM driver if the mount
hardware, your NexStar 8SE in this case, does not support the commands
in its serial command protocol to effect the movements that pulse
guiding demands. The fact that pulse guiding is available when using the
driver with unrelated mount models such as the AVX is of no matter. The
driver either interrogates the mount hardware upon connecting to it to
ascertain its capabilities, or the ASCOM driver maintains a capabilities
table of mount models and firmware revisions. Either of which would
inform how it advertises the various ASCOM capabilities, pulse guiding
included.

To my knowledge, the only way to guide the NexStar series is via
old-fashioned ST4. This is where you physically connect the guide camera
directly to the mount via the "telephone" cable with the RJ12 6-pin
modular connectors. PHD2 sends guide corrections to the mount via the
camera, which basically acts as a relay and ST4 interface for your
computer. You will want to have PHD2 calibrate following every major
slew. The NextStar series are geared towards visual observing and
novice, no-frills imaging. It doesn't surprise me that it's not capable
of pulse guiding via its ASCOM driver.

[G-Man 007]

That is a bummer :(

Appreciate the detail and information provided - I think my confusion came in because based on some documents and forums , all wrong I guess, it was my understanding that if a NexStar 8SE alt/az mount on wedge completes a polar alignment that the canpulseguide feature in the ASCOM driver would move from false to true allow for pulse guiding; however, it sounds like this is not the case due to the actual firmware of the mount.

When I first got my mount I used Celestron CPWI ASCOM Driver which allowed for pulse guiding under PHD2 independent of the firmware of the mount.  I then obtained SharpCap Pro 4.1 and wanted to use platesolving and syncing so that errors in the initial 4-star starsense alignment could be reduced to sub 1-arc minute for my imaging objectives for DSO.

Unfortunately, I found out the hard way that Celestron CPWI ASCOM Driver does not allow syncing of the alignment it conducts.  This forced me to switch to using the Celestron Unified Driver 6.1.7350 which allowed for syncing from SharpCap Pro; however, now I am learning that it can't do pulse guiding and as you indicated I would need to use ST4 guiding using my guide camera via on-camera mount on PHD2.  So I am left with a choice - guiding or syncing!!!!!!!

So I have to decide what is more important to what I am doing - platesolving and syncing or pulse guiding.  

Overall, this is very disappointing and I am not sure how to proceed at this point.  I really like using PHD2 and need to use guiding on my mount but also need to platesolve - anyway this is the issue as of now.

Thanks,

Edmund

[Bruce Waddington]

There's an alternative approach that will allow you to use PHD2.  In the PHD2 new-profile-wizard, specify 'on-camera' for the mount and then set the 'aux-mount' to your CPWI ASCOM driver.  This will do ST-4 guiding but PHD2 will still have the scope pointing information it needs for other things.  You won't have to recalibrate every time you slew the scope and you will get nearly all of the benefits that you would with pulse-guiding assuming your guide camera has guiding ability and you don't end up with USB and/or cable-routing problems.

Good luck,

Bruce

[Dale Ghent]

Ah that would be a much better arrangement to avoid the lack of PHD2 not having pointing information. The aux mount feature is easily overlooked.

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[Brian Valente]

This is also covered in more detail in the online help documentation within PHD

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/A671BBC4-B525-4FBD-8D52-0BBD40C401A2%40elemental.org.

--

Brian 

Brian Valente

astronomy portfolio https://www.astrobin.com/users/bvalente/ 

[Dale Ghent]

Cool. There is one issue this brings up, though. One would already have to know that the Aux Mount Selection section in the docs is relevant to ST4 in order to look there for guidance. By which point they would already be familiar with this info because they'd have to have already happen upon it by accident or have already read the entirety of the documentation. I'd say that either of those cases isn't likely, which makes this tidbit of info tough to come to know about.

There is a section on "ASCOM Benefits" which a person stuck with ST4 might skip past. Perhaps it might be helpful to have a "If ST4 is unavoidable" section that spells the configurations such a user could consider?

/dale

> On Oct 16, 2025, at 12:08, Brian Valente <bval...@gmail.com> wrote:
>
> This is also covered in more detail in the online help documentation within PHD
>

> To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/CAJa45i6wLoLKUnM9_ZXTJV2d%3D3_EmBn-7DDhqQ-D7%3Da1C7pM5Q%40mail.gmail.com.

[Bruce Waddington]

Hi Dale.  It's hard to argue against more or better documentation although we both know from the forum traffic that most users with questions have never looked at it.  The approach we took on this was to add a prompt in the new-profile-wizard that appears whenever the user chooses ST-4 (on-camera) guiding:

In fairness to the OP, he had never gotten this far, I think his question was more hypothetical.

Cheers,

Bruce

[G-Man 007]

To All,

That is a great discussion and it really helps.  Although I am not able to use CPWI ASCOM Driver since I already have Celestron Unified Driver 6.1.7350 on my computer and I have noticed that my system can't operate properly with 2 ASCOM drivers on my computers.  In any case, as you can see from the connections below the Aux Mount connects to the Celestron Unified Driver 6.1.7350.  

If understand all this properly, connecting to the Celestron Unified Driver 6.1.7350 via the Aux Mount in PHD2's "Connect Equipment" dialog will work functionally the same as using the Celestron CPWI ASCOM driver for the sole purpose of providing mount location information (e.g., current RA/Dec coordinates, pier side, and pointing state). Both are ASCOM-compliant telescope drivers that expose the mount's positional data to PHD2 without interfering with my primary on-camera (ST-4) guiding connection. Here's a quick breakdown:

Adding Aux Mount location data should help and I think here's how:

1.) Automatic Calibration Reuse and Accuracy:  Without location: PHD2 assumes a generic setup and may force full recalibration (multi-minute process) every session or after slews/meridian crosses, leading to inconsistent step-sizes.
With Aux: PHD2 reads RA/Dec/pier side, auto-adjusts calibration for orientation (e.g., flips Dec axis if west of meridian). I think I need to enable "Auto restore calibration" in Profile Settings > Advanced—so it reloads my last good calibration instantly, saving 5-10 minutes per night. On my Alt-Az, this also compensates for field rotation by flagging when to recalibrate (every 20-30° slew).

2.) Improved Star Tracking and Drift Compensation:  Location data lets PHD2 enable Dec compensation (treats alt axis like Dec) and pier side awareness, reducing errors from axis swaps. For your 8SE, set Guide Mode to "Alt/Az" or "Both Axes" in PHD2 > Brain tab—this predicts drift better, tightening RMS (total error) from ~1-2"/px to <1".  During guiding, it monitors coords to auto-pause/resume if the mount stalls (e.g., near zenith), preventing lost stars.

3.) Drift Align and Polar Alignment Aids:Run PHD2's Drift Align Assistant with Aux data for precise alt-az tweaks—shows real-time coord changes to minimize orthogonal drift (key for longer subs on unwedged setups).

Overall, I should see better guiding RMS and fewer "settle" failures, especially in poor seeing. I can imagine sub-1" RMS on 8SE with this hybrid (ST-4 + Aux location).

I hope I understood this correctly?

Thanks,

Edmund

[Brian Valente]

Edmund,

This feels like an AI response? It's not important to me but I'm not sure how much of that you wrote (and therefore understood) vs was written for you

The basic benefit is described in the dialog box - it gives you the pointing information that allows PHD to adjust its parameters based on sky position, which will improve guiding and reduce things like having to recalibrate

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/5c6af7da-5d5e-4ed5-83bf-9873f254c160n%40googlegroups.com.

[G-Man 007]

Brian,
You are correct - the response was from an AI (Grok).  I do apologize about not indicating so, but it just seems astrophotography is not an area of expertise readily accessible.  Therefore, I am left with the only option available to me which is to use an AI to get answers to various questions but again I should have indicated that it was from AI to the group.
With regards to my Email, the bottom part was from an AI and I do understand it, in part, since I have been at this for a few months but not sure if it is correct for PHD2 and I had copied it from a document I have created over time regarding various issues over the many months of doing this. The top part is me.  

Hope you will not hold that against me :).

As I said, I have been at this for months trying to resolve issues.  I think the AI is helpful about 50% of the time but really it ads to the confusion.

For example in this case, AI had indicated that if I was able to conduct a successful polar alignment for my NexStar 8SE Alt/Az mount on a wedge, then because it would be like a equatorial mount, the Celestron Unified Driver 6.1.7350 would switch from canpulseguide = false to canpulseguide = true.  Based on this, the AI indicated that I would be able to use the CUD to pulse guide my mount using PHD2.  However, when I followed up with Celestron they indicated that the firmware would not do this.

This is why I am here to get a real answer.

Thanks,

Edmund

[G-Man 007]

To All,

As a follow-up to my prior Emails regarding pulse guiding versus ST4 guiding, I was looking at the properties for Celestron Unified Driver 6.1.7350 and noticed the selection for track mode can be changed from alt/az to Eq N.  I did this to tell the mount that I am now using a wedge which I think would make my mount similar to a standard equatorial mount like the Celestron AVX mount.

Next, using the above, I specifically looked at the capabilities of the Celestron Unified Driver 6.1.7350 and as you can see from the illustration below that the change made has indeed cause an impact and canpulseguide is now set to true.

Finally, I moved to PHD2 to see if I can get the Celestron Unified Driver 6.1.7350 to be used in the mount guiding control.  As you can see now the Celestron Unified Driver 6.1.7350 connects to the mount.

So, now I am wondering if I can now use this methodology to actually pulseguide my NexStar 8se alt/az on a wedge which again is similar to an equatorial mount?

Finally, in manual guide in tools with guide pulse duration (ms) set at 5000, I tested my mount to see if I could hear any noises and sure enough I did.  Please note, I have removed the ST4 wire from my ZWO ASI220mm-mini guide camera.

Does this mean I sent a pulse guide signal to my mount or am I imagining things?

Thanks,

Edmund

[Brian Valente]

Edmund

Run it and see 

To view this discussion visit https://groups.google.com/d/msgid/open-phd-guiding/c7977e26-5223-4fe3-80e5-674dd01f7313n%40googlegroups.com.