Meridian Flip and PHD2

Sequence Generator
1

After a meridian flip PHD ran into an error saying it was too far north and to re-calibrate. I closed the error and it resumed to normal. Can SGP force a calibration after a flip on the same target or is there a way to stop this error from stopping SGP?

Thanks
–Rob

2

Rob:
Ideally, calibration should be done near the celestial equator. If you try to calibrate really far from the celestial equator, not sure just how far, PHD issues that notification.
But, there should be no need to recalibrate just because the mount flipped. If you are doing so at every flip, you are wasting sky time.
In the PHD BRAIN settings, the box labelled “Clear mount calibration” should be unchecked, except when you WANT to recalibrate. The box labelled Auto restore calibration should normally be checked.
You may, or may not, have to toggle the “Flip Calibration Data” button on the Guiding tab of the SGP control panel . . . depends on your guider according to the tool tip. I’ve never needed to do so with my own gear.
I add this merely because I was recalibrating far more often than necessary until I had this pointed out to me.
There is a box in the SGP control panel to force recalibation on a new target but I don’t quite understand why that would be “a good thing” for most of us?

I will leave for others to state if SGP can force a recal. after PHD throws up the notification. Even if it can, it seems a poor practice to force a recal. further from the C.E. than PHD suggests.

3

Well I went from a polar alignment straight into the sequence to image ngc7635. When the sequence started I had the force recalculate on and PHD2 did so without problem. Everything was fine until the flip. After the flip it showed the warning, not really an error but it stopped my sequence. I closed the warning and everything continued fine.

Not sure how to address this but I don’t think I should have to manually calibrate. If I do it kinda defeats the purpose of force re-calibrate as a equipment profile item. All my other flips being closer to the celestial equator work fine, and wouldn’t get the warning. I would be happy if the warning could be ignored. Not sure what other options exist.

Maybe the Flip Calibration Data isnt working right since it’s already calibrated when it did the first calibration that far north. Why would a flip change that?

–Rob

4

As is so often the case in forums such as these, I am not sure we fully understand each other. :slight_smile:
I got the impression you were running with the PHD “Clear mount calibration” box checked. If so, well, why? If not, I have no explanation as to why PHD would have ordered a recal. after the flip. I have never experienced a recal. attempt after an autoflip myself. And I certainly would not want the software to recal. at a far northern dec. when I was using a valid cal. done near the C.E. prior to the flip.
And I have no explanation as to why you were able to initially cal. at a far northern dec. with no notification, only to have the notification pop up after the flip. Obviously, the dec. did not change. That beats me . . . UNLESS the “Clear mount cal.” box is checked. Having that box checked would certainly cause a recal. attempt after the flip. But I would reiterate again, that calibrating at decs far from the C.E. is not good procedure. From the PHD manual . . .
“If you’re using an ASCOM (or Indi) connection for either the ‘mount’ or ‘aux-mount’, a good calibration can be re-used for a long time, and that is the preferred way to operate. These connection options allow PHD2 to know where the telescope is pointing, so a calibration done at one point in the sky will be automatically adjusted as you slew to different targets. The old method of having to re-calibrate whenever you slewed the scope or switched the side-of-pier is a thing of the past so long as PHD2 has pointing information. With this type of set-up, you would only re-calibrate if you rotate the position of the guide camera by more than about 5 degrees or make other major changes to the hardware configuration. In general, the best practice is to get a good calibration within about +/- 20 degrees of the celestrial equator and high enough in the sky to avoid major seeing (turbulence) problems.”

5

In PHD2 the “Clear mount calibration” box is not checked.

DebugLog just after the flip…
22:03:45.418 03.366 7604 Exposure complete
22:03:45.499 00.081 7604 worker thread done servicing request
22:03:45.499 00.000 5736 OnExposeComplete: enter
22:03:45.499 00.000 5736 UpdateGuideState(): m_state=5
22:03:45.499 00.000 5736 Star::Find(15, 76, 542, 0, (0,0,0,0), 0.0) frame 3
22:03:45.499 00.000 5736 Star::Find returns 1 (0), X=76.17, Y=542.87, Mass=495808, SNR=61.5, Peak=56512 HFD=3.0
22:03:45.500 00.001 5736 Changing from state 5 to 6
22:03:45.511 00.011 5736 ScopeASCOM::GetDeclination() returns 61.2
22:03:45.512 00.001 5736 ScopeASCOM::SideOfPier() returns 0
22:03:45.512 00.000 5736 AdjustCalibrationForScopePointing (scope): current dec=61.2 pierSide=0, cal dec=61.2 pierSide=0 rotAngle=None bin=1
22:03:45.512 00.000 5736 GetDouble("/profile/2/camera/pixelsize", 0.000000) returns 3.750000
22:03:45.512 00.000 5736 skipping Dec comp: initial calibration too far from equator
22:03:45.512 00.000 5736 Alert: Calibration was too far from equator, recalibration is needed.

I’ll look into re-use of the calibration. I am mobile and setting up each night so I don’t know if that would upset any previous calibrations.

Thanks!

6

@rmorgan,

You can re-use your PHD2 calibration from night to night as long as your guide camera orientation is the same. You can mark the position of the guide camera with a piece of tape or something like than and that will be quite accurate enough to re-use your calibration night to night. Select the Auto restore calibration option in PHD2 on the guiding tab in the brain.

Calibrate PHD2 once with the scope pointed near the meridian and near declination 0. Once you get a good calibration, you don’t need to re-do it unless you change the orientation of the guide camera. You don’t want PHD2 calibrating at all during your SGP imaging run–it’s not necessary and opens up the opportunity for something to go wrong. Make sure you un-check the option in SGP (Auto Guide tab of control panel) “Re-calibrate auto guider when target changes”.

After you do your initial calibration it’s a good idea to confirm that PHD2 is working as expected on both sides of the meridian. To confirm this you would stop guiding, slew the scope to the other side of the meridian (do a pier flip), then start guiding again. PHD2 should guide normally after the pier flip. Having confirmed this you can be confident that it will work just as well during your SGP sequences.

Andy

P.S. the “Clear mount calibration” check-box on the Guiding tab in PHD2 is not really an option in the ordinary sense of a setting that you enable or disable. It just causes the current calibration to be cleared when you click OK, forcing a new calibration the next time you start guiding.

7

I did the manual calibration and running the sequence now. Everything seems to be working and the flip went fine.

Would moving the mount from site to site be cause for a re-calibration? Sounds like I may not have to worry about it.

Thanks for the help Terry & Andy.

8

Calibration in PHD2 measures two things:

  • calibration angle: which direction does the star move on the guide camera chip in response to RA and Dec guide pulse commands. This is determined by the orientation of the camera. Same camera orientation => same calibration angles
  • calibration rate: how far the star moves along each axis (RA, Dec) in response to guide commands. This depends on your mount’s guide speed setting and your guide scope image scale (arcsec per pixel)

In other words, these are all factors of your guide setup, unrelated to the site. One caveat is that if your polar alignment is very far off when you do your first calibration before you do an accurate polar alignment, then may want to re-do the calibration after your polar alignment since the polar alignment can change the calibration angles a little bit.

9

As another Nomadic astrophotographer, here is a workflow that might work for you, too…

  1. After everything is up and connected and the main camera is roughly focused, I start the PHD2 polar alignment tool.
  2. Next, do the first slew which puts the scope at the celestial equator and meridian.
  3. Let PHD2 calibrate (unless I was already set up from the previous night, like at a star party… then just “restore calbration”)
  4. Let the PHD2 guiding assistant run for a few minutes. Determine whether the polar alignment is adequate or if it needs to be refined.
  5. Accept PHD2’s guiding suggestions and proceed to polar alignment refinement, if necessary, or if it is good enough, you are ready to image.

Most of this can be accomplished in astronomical twilight before you would want to start your imaging run.

Something that I settled on over the last several months that seems to work pretty well…

Best regards,
Craig

10

Thanks Craig… I may end up following your steps a bit closer. My new goal is the following steps and maybe remove #3 completely. I came very close to this last night if it wasn’t for installing a new ASCOM driver and the initial PHD calibration. Subsequent nights I should be able to remove steps 1,2, and 3.

  1. Setup and level mount
  2. Polemaster alignment
  3. Plate Solve and Test guiding
  4. Run Sequence
  5. Walk around the observing field. Do visual observing at the DOBs.
  6. Wake up to the end sequence alarm
  7. Cover scope
  8. Process subs and setup next sequence

I wish SGP could interface with PixInsight so I could automate the sub processing.