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PHD2 adds multi-star guiding...

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#1 StephenW

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Posted 02 December 2020 - 05:35 PM

Just saw it listed in the new release: https://openphdguidi...ment-snapshots/

 

You can enable the feature under the Guiding tab in the Brain

 

Haven't had a chance to play with it yet - hopefully tonight if the weather holds...

 


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#2 imtl

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Posted 02 December 2020 - 05:45 PM

Nice! Gonna try this tomorrow!


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#3 endless-sky

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Posted 02 December 2020 - 06:08 PM

I have been wondering why PHD2 didn't have this feature since the moment it got introduced in EKOS internal guider a good while ago.

I never liked using EKOS internal guider, as it always gave me worse results than PHD2, whether I used the feature or not. I also like PHD2 Guiding Assistant and the many available polar alignment routines.

With the addition of this long awaited feature, now PHD2 finally has the only thing that it was missing.

I can't wait to try it out! I hope this feature will make the seeing fluctuations (and their negative impact on guiding) less of a problem and allow for shorter guiding exposures.

Edited by endlessky, 02 December 2020 - 06:09 PM.

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#4 Stelios

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Posted 02 December 2020 - 06:38 PM

The truth will be in the pudding. 

 

We'll see if this results in better guiding. Unless there are clouds, I don't frankly see that it would make much of a difference. 


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#5 Peter in Reno

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Posted 02 December 2020 - 06:41 PM

Didn't Maxim added multi star guiding and wasn't the result no better than single star guiding? 

 

Peter 


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#6 NightBear

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Posted 02 December 2020 - 06:45 PM

I imagine this will improve guiding in bad seeing because it can average out the fluctuations between stars, thus reducing the required corrections and avoid chasing the seeing. I'm going to try it out right now!


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#7 imtl

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Posted 02 December 2020 - 06:48 PM

I imagine this will improve guiding in bad seeing because it can average out the fluctuations between stars, thus reducing the required corrections and avoid chasing the seeing. I'm going to try it out right now!

Report! with screenshots! :p



#8 AZ Maverick

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Posted 02 December 2020 - 06:49 PM

The truth will be in the pudding. 

 

We'll see if this results in better guiding. Unless there are clouds, I don't frankly see that it would make much of a difference. 

 

I agree if you are using a separate guide scope, almost all of my stars were pretty much the same when I was guiding that way.

But I'm hoping that it might help improve my OAG guiding.

Sometimes PHD2 picks a star at the field edge that is technically the best star, but it is many times misshapen and the centroid is pretty wild - maybe multi star guiding will help in tightening up that centroid.

Guess I'll see also. 


Edited by AZ Maverick, 02 December 2020 - 06:51 PM.

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#9 Jim Waters

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Posted 02 December 2020 - 06:58 PM

Interesting.  Somebody needs to report back.


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#10 NightBear

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Posted 02 December 2020 - 07:00 PM

Looks like it's working snazzy so far. There doesn't seem to be any feedback as to what it is doing with the multiple stars though.

 

phd.jpg


Edited by NightBear, 02 December 2020 - 07:00 PM.

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#11 Jim Waters

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Posted 02 December 2020 - 07:04 PM

Is the guiding / graph any better than before?  Have you done a meridian flip and started guiding after that?


Edited by Jim Waters, 02 December 2020 - 07:05 PM.


#12 imtl

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Posted 02 December 2020 - 07:04 PM

So, I assume the star profile is an average of all the guide stars? It seems that there is no control of anything there really, correct? You cannot choose the number of guide stars or anything else regarding this?

 

Maybe its worth turning this off for 10-15 minutes and take another screen shot to compare. Seeing looks quite steady for you tonight.



#13 AZ Maverick

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Posted 02 December 2020 - 07:05 PM

Looks like it's working snazzy so far. There doesn't seem to be any feedback as to what it is doing with the multiple stars though.

 

attachicon.gifphd.jpg

What Jim Waters asked...

 

From the online manual regarding how it works:

Attached Thumbnails

  • MultiStar.JPG

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#14 Jim Waters

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Posted 02 December 2020 - 07:10 PM

I will try it out tomorrow night and see how it plays with N.I.N.A.



#15 NightBear

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Posted 02 December 2020 - 07:14 PM

I am now guiding at 1s exposures instead of 2s and my guiding has gotten even better apparently. Which lends credence to my notion about multi-star cancelling out seeing fluctuations.

 

phd2.jpg

 


Edited by NightBear, 02 December 2020 - 07:18 PM.

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#16 Jim Waters

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Posted 02 December 2020 - 07:14 PM

 I don't frankly see that it would make much of a difference. 

Just one of those technical whizzy fancy things? 

 

EDIT:  I am more interested in the - "Bug fix: ensure Dec comp is applied when meridian flip is accompanied by a Dec slew" 


Edited by Jim Waters, 02 December 2020 - 07:16 PM.


#17 NightBear

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Posted 02 December 2020 - 07:24 PM

Here is with multi-star disabled. As you can see, substantially worse guiding without it enabled.

 

phd3.jpg


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#18 Jim Waters

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Posted 02 December 2020 - 07:26 PM

Nice, but are the stars better in your images?  Thanks for the post NightBear.


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#19 NightBear

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Posted 02 December 2020 - 07:32 PM

Nice, but are the stars better in your images?  Thanks for the post NightBear.

I haven't taken any exposures yet, I'm waiting for my target to get over the neighbor's roof :D

 

I will try taking a few test long exposures of plain sky and measure the eccentricity with PI. Will report back in a bit with results.


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#20 Jim Waters

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Posted 02 December 2020 - 07:34 PM

Thanks...!

#21 fewayne

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Posted 02 December 2020 - 07:45 PM

I just was in an interesting thread over at the INDI fora about the multi-star guiding in Ekos. My question was pretty specific: Do seeing variations occur on a small enough angular scale for our scopes that the various stars being guided on can be treated as independent? And if so, can we shorten guide exposures, since the seeing-related variations will be random and tend to cancel each other out?

 

I'm interested in this because in certain conditions I've seen significant improvement with shorter guide exposures; my hypothesis is that my particular mount with my particular load has to be shepherded pretty closely lest it wander off in 3 seconds or so.

 

The answer was "well it's pretty complicated so it depends and the jury is still out".

Still, that's a potential benefit. My interlocutors referred back to this CN thread, which I found fascinating.

 

ETA: At least the answer to the first question is relatively well known: Yes. Seeing variation occurs in cells small enough and high enough that we can treat them as independent.


Edited by fewayne, 02 December 2020 - 07:46 PM.

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#22 NightBear

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Posted 02 December 2020 - 08:18 PM

Results inconclusive with only 6 data points. I'd gather more but I have other stuff to do tonight! It's possible the exposure was too long for Lum and the stars are just over-exposed. I can try again with a color or NB filter another time.

 

phd4.jpg


Edited by NightBear, 02 December 2020 - 08:27 PM.


#23 stardustborn

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Posted 02 December 2020 - 08:46 PM

It seemed that dithering would occasionally cause a star near the edge to be lost and now that won't happen as much?


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#24 dhaval

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Posted 02 December 2020 - 08:56 PM

I am hoping this helps us folks with long FL scopes and OAG.

 

I will be testing it next clear night. But excited about this feature.

 

CS!


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#25 AZ Maverick

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Posted 02 December 2020 - 09:36 PM

It seemed that dithering would occasionally cause a star near the edge to be lost and now that won't happen as much?

 

I don't think so.

The way I read it, PHD2 will still pick whichever star it thinks is the best even if it's on the edge - the other stars just refine the centroid.

When I use the auto select star, if I think it's too close to the edge for dither then I go ahead and manually choose one a little closer in - but it has to be really really close to the edge before I worry about it.


Edited by AZ Maverick, 02 December 2020 - 09:37 PM.

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