Re: Problem with PHD2 when also connected to Mach1 mount using Stellarium's Telescope Control plugin

Dale Ghent

Just looking through your posts, my first inclination is to check the tracking rate that the AP ASCOM driver is reporting while this condition is happening and verify that it's in sidereal; not lunar, solar, or some other tracking rate. I just looked at the source code for Stellarium's TelescopeControl plugin and it does not manipulate tracking rates at all. PHD2 doesn't manipulate tracking rates at all, so if the driver is reporting a sidereal tracking rate and not some other or custom rate, then tracking rates can then be excluded from a possible cause.

As for your frustrations, I think one must appreciate the many-layered cake that astro software stacks are. This necessitates some solid demarcation of responsibility among software maintainers when it comes to these different components interacting between each other. In this case, things work fine when Stellarium isn't in the mix, but go south when it is. Since the stack is designed such that PHD2 should not have to do anything special if Stellarium (or any other particular item of software) is involved in running things, the first advice is to determine why the act of using Stellarium alters the situation.

There is often a "shoot the messenger" mentality because one piece of software is surfacing a bug or misconfiguration that exists in a different part of a kind-of-complex stack. The best way to debug these kinds of issues is to deconstruct things and first look at the common components such as the driver and verify that its reporting sane settings - it is, after all, the canonical source of information about the mount. There is also the completeness of the problem description to consider. There's often a tertiary actor involved that the user leaves out of the description because they think it's irrelevant, but that can very well not be the case.

On Jan 9, 2022, at 00:38, John Davis <johncdavis200@...> wrote:

Unfortunately the knee-jerk response from the PHD2 support forum is “oh it’s a Stellarium problem – go ask them” or they are trying to tell me I’m not using the AP ASCOM driver to communicate to Stellarium (I am).

As a software tester – I’m used to developers always assuming that it CAN’T be THEIR software that has the bug…. Sigh.

Seeing what you have experienced, I have seen some odd behaviors like that as well – not *exactly* the same – but cases where stars just start tracking off without any explanation.

I know that PHD2 is good – but I got to think that the new multi-star guiding code just might still have some bugs in it. I’m just skeptical that PHD2 has NOTHING to do with any of this.

I’ll let you know if I find anything else on another board.

From: <> On Behalf Of Joel Short
Sent: Saturday, January 8, 2022 11:21 PM
Subject: Re: [ap-gto] Problem with PHD2 when also connected to Mach1 mount using Stellarium's Telescope Control plugin

Oh my word John! I MIGHT have observed something similar, but this is with a different mount (CEM120EC). When I first slew to near the meridian/celestial equator in order to do a PHD calibration, I get this:


The stars keep trailing like this for over a minute until finally it somewhat stabilizes, but even then the stars will oscillate back and forth over about 5-6 star widths. This is definitely NOT expected behavior for this mount, and I've observed this a few times this evening. It is unnerving.

After reading your post I closed PHD and Stellarium, manually slewed to the same spot and immediately started PHD and started looping images (started within 5s of slewing to the spot). The stars stayed bang on immediately. No having to wait a minute for the mount to stop moving and no oscillation.

I can't say this is the same issue, but I'm certainly going to keep my eye on this and see where it goes. Thanks for posting this.


On Sat, Jan 8, 2022 at 9:13 PM John Davis <johncdavis200@...> wrote:


I have been seeing this problem for several months now, and I would like some input as to what the nature of the problem might be.

**NOTE: I have also sent this same post to the PHD2 support group **
Just thought I'd send it to the AP list too - in case someone here had experienced and solved the problem.

To summarize, I am seeing problems with PHD2 guiding - most often the RA tracking - when I am running a guiding session in PHD2 and have the mount also communicating with Stellarium via the Telescope Control plug-in.

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