Automated meridian flip

I am brand new to SGP and have been reading about the automated meridian flip routine. I make use of a camera rotator and when doing a manual meridian flip, I always rotate the camera 180 degrees as part of that process. The SGP (2.3.15) documentation does not mention camera rotation as part of the automated meridian flip, so I was wondering if camera rotation is part of the process?

Charlie Miller

Not currently, although we may add in in a future release. The issue is that PHD would likely need to recalibrate or be aware of the rotation as well.

However one of the PHD2 authors has also mentioned wanting this behavior so I would assume that he can/has added support to PHD2.


That work has already been done and rotator support has been added to PHD2 :smile: I haven’t published a build with the feature yet, but I can do that now if you want to give it a try.


I would be happy to test the camera rotation feature in PHD2. Let me know what I need to do.

Charlie Miller

Hi Charlie,

I believe you have the Pyxis LE, right? (I saw you post recently about the LE in the the QSI yahoo group).

There is a problem with the Optec ASCOM drivers in that they only allow connections from a single app at a time. If SGP is connected to the rotator, then you will not be able to connect to the rotator in PHD2. I brought this issue to Optec’s attention and they are currently working on fixing their ASCOM drivers.

In the meantime, I wrote an ASCOM driver of my own to control the Pyxis 2" and 3" rotators (I have a 2") which supports concurrent connections from SGP and PHD2. This new driver will not work with your LE. I contacted Optec to get the LE command protocol and when I get this I will update my ASCOM driver to support your LE. I’ll let you know when that is done so you can do some testing.

If you wanted to test PHD2 only, then that is simpler. I’ll put a build up on later tonight with the rotator support (it will be v2.4.1c). PHD2-related questions can be discussed at the PHD2 google group.



Yes, I use an Optec Pyxis LE with my QSI 683wsg. I will download the update to PHD2 Guiding and install it. If the weather cooperates, I will go to my observatory this weekend to make some tests.



I installed v2.4.1c on my home PC to take a look at it. I see how to configure the Pyxis LE rotator. I would like to verify that the test procedure would be:

  1. Establish guiding with a target just east of the meridian
  2. Stop guiding and perform a meridian flip of the scope
  3. Rotate the camera 180 degrees
  4. Tell PHD2 that a camera rotation has occurred
    by opening the Advanced Setup tab, selecting the Rotator tab
    and then checking the “Reversed” check box.
  5. Resume guiding.

Do I need to reselect the same guide star or will PHD2 try to find the same guide star and also know to reverse calibration?


In the Connect Equipment window, select your Rotator and connect. Once you do that, PHD2 will automatically adjust calibration for the rotator angle, so step 4 is not needed.

The Reversed checkbox is for telling phd2 whether the angles reported by the rotator need to be reversed due to the optics flipping the image relative to the sky. To determine whether you need this setting:

  1. calibrate and start guiding
  2. stop guiding
  3. move the rotator a good amount, say 90 degrees
  4. start guiding

Guiding should be good after the rotation. If not, you probably need to check the “Reversed” option (set it and forget it … it won’t change unless you switch to a new scope.)

Before attempting a meridian flip with the rotator, you should make sure meridian flip is working without the rotator. You’ll need to be connected to an ASCOM mount, or, if you are using an ST-4 connection to the mount, use the ASCOM driver for the Aux Mount.

  1. calibrate
  2. start guiding near the meridian
  3. stop guiding
  4. flip the mount
  5. start guiding (same star or different star)

Guiding should be good after the flip. If not, try the option “Reverse dec output after meridian flip” on the Mount tab in the Brain. Some mounts require this, some do not.

Once you have confirmed that both rotation and meridian flip are working independently, you can try them together with your test procedure (excluding step 4).

You’ll almost certainly want to use the “Auto restore calibration” option in phd2 (global tab of brain); if things are working as expected, you will not need to recalibrate regardless of rotator angle or side of pier.



Thanks for the clarification. You have clearly put a lot of work into PHD2 to handle this rotation capability.

Snow / sleet is predicted for central Texas this weekend, so may not get to test as soon as I would like.

Charlie Miller


I was just reviewing the SGP tutorial on automatic meridian flip:

This video seems to show that camera rotation is already a part of the meridian flip logic:

When you look at the before-flip camera frame and the after-flip camera frame (M33) you can clearly see the after-flip frame is rotated 180 degrees. The PHD2 auto guiding seems to resume properly in the tutorial.

So I am a little confused on the status of camera rotation support during meridian flips.


Hi Carlie,

The rotator can be used for the initial framing of the target, but SGP currently will not move the rotator as part of the meridian flip.

For those of us with rotators, we would like to have the option to rotate 180 degrees after the flip so we can continue guiding on the same star. Ken and Jared have added this feature request to their backlog (see this thread).

In the meantime, until this feature is implemented, you would need to use the meridian flip option to pause before the flip, and rotate manually when it pauses.


Just to close the loop on this: I received the necessary info from Optec, but the LE uses a completely different interface (USB, not RS232), so I cannot really go any further without an actual LE rotator to test with. The best thing to do is to wait for Optec to complete their new ASCOM driver with concurrent connection support.



It looks like Optec ended up taking a different route. They created a hub similar to the ASCOM Generic Hub or POTH hubs included with the ASCOM distribution, except supporting rotators as well.

You should be able to use their hub to connect your Pyxis LE rotator to both PHD2 and SGP.



I just saw Jeff’s post on the Optec group. I will install their hub and
see how it works. I am also interested to see if their hub will allow me
to activate the TCF-Si focuser’s temperature compensation routine directly
in the Optec GUI and still allow SGP to perform auto focusing.

Central Texas is showing clouds for the next several nights, so it might be
a while before I get to do this.