Calibration Assistant - meridian offset

[Stuart Taylor]

Presumably the ideal calibration location is RA zero, Dec zero

My CA seem to have a default of 5 degrees meridian offset. Is there a reason for that, or should I just set it to zero?

Thanks

[Brian Valente]

ideal calibration is Dec 0, I think you meant HA=0? not RA

5 minutes off is so it will slew to pier side east, that way you aren't running into any limits or crashing into your pier

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[Stuart Taylor]

No, I meant RA zero. I thought it was best to calibrate on the equator and the meridian. But maybe I have misunderstood.

[Brian Valente]

RA is not at the meridian. HA=0 is that the meridian

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[Brian Valente]

I should say RA = 0 does not equal meridian. Certainly RA=0 could be at the meridian ;)

HA = 0 is at the meridian

[Stuart Taylor]

sorry, I am talking nonsense. meridian is Az=0 not RA = 0 (facepalm)

WHat is HA?

[Stuart Taylor]

so back to my original question, why would I not want to calibrate at the meridian? (the calib assist has an offset of 5 degrees, which presumably means it will slew to 5 degrees before or after the meridian to start calibrating)

[Brian Valente]

See my original response re: avoiding pier crash or limits

On Tue, Nov 14, 2023 at 10:09 AM Stuart Taylor <sctayl...@gmail.com> wrote:

so back to my original question, why would I not want to calibrate at the meridian? (the calib assist has an offset of 5 degrees, which presumably means it will slew to 5 degrees before or after the meridian to start calibrating)

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[Stuart Taylor]

I am getting truly horrible guiding tonight. I ran the CA at the meridian, then ran the GA for about 5 mins and took the recommended actions. The dec backlash on this mount is large, so I have just been trying to guide south only in Dec. But still it's not guiding well. The RA is guiding badly too!

What can I do about this?

https://openphdguiding.org/logs/dl/PHD2_logs_MSxt.zip

[Brian Valente]

after you calibrated, your 3 min session was 0.86" total rms. would you call that "truly horrible"?

then you proceeded to fiddle with settings and adjust values that aren't going to make any difference, and then you disabled Dec guiding, which certainly isn't going to help your rms ;)

So maybe re-enable dec guiding and stop fiddling with things. I'd say let it run for a while. You are barely into letting PPEC do its job

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[Stuart Taylor]

It was about 1.2" - 1.4" total, I thought. Hence why I ran guiding asst and got this - see screenshot -  (which recommended guiding in one direction only). The values that I adjusted "that aren't going to make any difference" were the suggestions of the guiding assistant. I don't understand this stuff at all, so I rely on GA to give me advice.

I'll try what you suggest.

Many thanks Brian.

[Brian Valente]

If you looked at your actual guiding, it was fine

leave dec guiding = auto

increase your Dec auto backlash compensation to 800, set max 2500 (just a starting point, not sure what is the actual backlash amount)

it will settle down to find the correct value

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[Brian Valente]

PS

>>>The values that I adjusted "that aren't going to make any difference" were the

that was my bad, sorry. I thought you were adjusting the settings as it was running, my mistake

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[Stuart Taylor]

Sorry, what do you mean by my "actual guiding"? I am currently getting 1.25" (when I normally get 0.5" on average). That's a big difference (hence why I described it as horrible).

Thanks

[Brian Valente]

Did you pull up your guidelog in the log viewer?

this was your 3min run after the Calibration

then you started fiddling with things, including messing with the Dec backlash and guide mode

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[Stuart Taylor]

Yes, I did look in the log viewer. Ok, so the adjustments you are suggesting are these right?

Thanks so much for your help

[Brian Valente]

yes but also check the Enable box

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[Stuart Taylor]

ok. Done. I'll see if that improves things over the next hour or so. Thanks

[Brian Valente]

yep

send the guidelog if you want a check in

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[Stuart Taylor]

Brian, is there a way to force the guide log to be written while guiding? Or do I have to hit the stop button to get it to add the most recent data?

[Brian Valente]

You don't need to do anything, it writes to it constantly

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[John Nagy]

You can even open the PHD Log Viewer tool and read the file while it's being written too. You have to refresh the Log Viewer by re-opening/reading the file occasionally but it won't affect the integrity of the file (at least that's been my experience).

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[Brian Valente]

>>> You can even open the PHD Log Viewer tool and read the file while it's being written too. You have to refresh the Log Viewer by re-opening/reading the file occasionally but it won't affect the integrity of the file (at least that's been my experience).

yep

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[Stuart Taylor]

so the guiding initially got worse after I made the changes to dec comp, but then there was a meridian flip and things got dramatically better.

Could this be something to do with my balance? As I am now on the east side of the pier?

Just fyi, my PA was particularly good tonight if that's of relevance. I am usually over an arcmin, but tonight I got down to about 30"

[Stuart Taylor]

https://openphdguiding.org/logs/dl/PHD2_logs_JTUx.zip

[Bryan]

FYI

here is what the Best Practices state

- Within +/- 20 degrees of celestial equator (Dec=0)
– Within an hour of celestial meridian

The Calibration Assistant will adjust much closer than this, but the point is you can be some distance from the equator and zenith and still get a good calibration, assuming all the other settings are correct.

Bryan

[Brian Valente]

Hi Stuart

in your first run pier side west (eastern sky) RMS was indeed higher in both RA and Dec. you had many lost star events, I assume these were displayed to you as well?

The second run on opposite side of pier, the guidestar SNR looked better, low but look at the difference

I suggest you increase the auto find SNR to something reasonable like 20-30 and make sure you have an appropriate dark for your guide camera exposure time (you do, but something to keep in mind). 

Brian

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[Stuart Taylor]

many many thanks for this very helpful advice. Yes, I was getting frequent lost star events. I always tend to assume this is due to wisps of high level cloud obscuring the guidestar.

[bval...@gmail.com]

Sorry i missed this:

>>> WHat is HA?

Hour Angle