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PhotoGav

PHD Graphs - Spot The Difference...!

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Here is my PHD graph while imaging M51 on 9th April:

post-29321-0-26826100-1397863368_thumb.j

Himalayan, but the subs were spot on with lovely round stars.

And here is my PHD graph from now, 19th April, imaging M51 some more. I think I'm even on the same star for guiding:

post-29321-0-05236500-1397863447_thumb.j

Flat line..... The subs are spot on with lovely round stars.

The wonderful thing is that the subs are lovely and hopefully I will be able to build a good M51 from all this data. However, the obvious question is: why the polar difference in PHD graphs when things are basically the same. Well, when I say the same, I am lying really. The optical equipment is all the same, but I do have a lovely new, more powerful, laptop running things now and it is running a slightly newer version of PHD. Can those two things really make such a difference? Also, could much clearer seeing and no moonlight add to make that much difference?

It doesn't really matter as the thing that does matter is the quality of the subs and they seem to be good, but I just wonder why the big difference?!

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I suppose I should know how it works but if the stars are nice and round I don't care.

Have a screen grab of the graph but it's down in the obsy.

My graph, the blue and red lines stay very close to the centre line and rarely hit the first

mark up or down.

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Mine used to look like an earthquake line but a new mount has them as flat as the wash.

oddly, I used to get round stars too. But they were very bloated.

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It's not unusual to see quite a difference between guide traces at the start and end of a night, as the seeing improves and the air cools and settles down.  So seeing a difference between days isn't completely unexpected.

I've swapped mounts before during the same night, using one at 2200 and another at 0400 and thought 'wow, what an improvement', only to see the second mount mirror the performance of the first at 2200 the following night, and then settle down as less thermal turbulence comes off nearby houses etc.  Then I remembered reading something similar in a book 20 years ago...

Sometimes the kit does just work better now and then though.

Jack :grin:

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Hi

My guiding was very good last night - probably better than any time recently. But got eggy stars :( Dunno why - so I did a polar alignment even though everything was fine on Sat night, but didn't seem to help and the guiding got worse. It should have been a great night's imaging but it turned into a bit of a disaster :(. Rebalanced everything today but it's uncertain whether it'll be clear enough to check out tonight. If it's not one thing, it's another! Sigh.

Louise

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You're not alone Louise, this happens to everyone.  Differential flex between guidescope and imaging scope, or focuser sag (which amounts to the same thing).  Dithering, where the next sub starts a bit early, can give you the problem too.

I think it's more frustrating for us in the UK, because we know we're unlikely to get another clear night straight after losing one to technical gremlins or just being a biff...(me, always).

Chin up,

Jack

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You're not alone Louise, this happens to everyone.  Differential flex between guidescope and imaging scope, or focuser sag (which amounts to the same thing).  Dithering, where the next sub starts a bit early, can give you the problem too.

I think it's more frustrating for us in the UK, because we know we're unlikely to get another clear night straight after losing one to technical gremlins or just being a biff...(me, always).

Chin up,

Jack

Hi Jack

Yeah very frustrating and clear nights in Glasgow are especially rare! Nights are shorter up here (than down in the south of England! ) during the summer so that doesn't help. Was hoping to check things out tonight but it's just murk lit up by lp :(. Oh well, will have to be patient!

Cheers

Louise

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A flat guiding graph should mean that all is OK but saddly this is not so. Many factors affect the guiding and even more factors affect imaging, the balance of the mount, the dynamic balance of the scope,  the seeing conditions  amongst many before one considers the stability of the imaging camera in the focuser in different orientations this is particularly the case with the Newtonian scopes. Three nights ago I had a graph line as flat as a pancake, last night with exactly the same set up I was having zig zag lines all over, I stopped the guiding slewed to some other part of the sky and then came back and then I had  a flat line again for nearly 5 hours of imaging  . If the graph is not flat you could still have round stars but these are not as tight as they ought to be due to the mount constantly correcting in both the DEC and RA. Guiding is indeed a black art .

A.G

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A flat guiding graph should mean that all is OK but saddly this is not so. Many factors affect the guiding and even more factors affect imaging, the balance of the mount, the dynamic balance of the scope,  the seeing conditions  amongst many before one considers the stability of the imaging camera in the focuser in different orientations this is particularly the case with the Newtonian scopes. Three nights ago I had a graph line as flat as a pancake, last night with exactly the same set up I was having zig zag lines all over, I stopped the guiding slewed to some other part of the sky and then came back and then I had  a flat line again for nearly 5 hours of imaging  . If the graph is not flat you could still have round stars but these are not as tight as they ought to be due to the mount constantly correcting in both the DEC and RA. Guiding is indeed a black art .

A.G

Hiya

Hehe - it's definitely a black art here! Hopefully my setup is well-balanced now (as per Dion's really helpful youtube video on the subject :) ). Things are not helped by the limitations of my window frame keeping the scope low.. I think I'll order one of the pedestal mounts from Orion Optics next week. A shortish one should enable me to point the scope higher in the sky away from the worst of the lp and the murk. I'll have to do some measurements to see what the optimum height would be. A lower scope mount would seem a good investment. My guiding graphs are usually quite zig-zaggy and I know a lot of that is due to atmospheric conditions. The graphs improve considerably if I can use longish phd exposures - say 4s. That seems to effectively iron out quite a lot.

Hope we get some more clear skies soon!

Cheers

Louise

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It does indeed seem to be a 'black box solution' - quite what and how it happens is far beyond me. Interesting you say that even if guiding seems to be working well, a bumpy graph will give not as round stars as a flat graph.

One thing I have learnt the hard way is to avoid guiding on dots that aren't stars...... Doh! Great graph - very unround stars!!

Sent from my iPhone using Tapatalk

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I'd be happy if I could just get mine guiding lol, tried again on Saturday but it was having none of it but slowly getting there I guess.

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Hi Tich

What's the problem? What are you having difficulty with?

Louise

Edited by Thalestris24

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Hi Tich

What's the problem? What are you having difficulty with?

Louise

Well where do I start lol

PHD recognises the camera a QHY5L-II managed to get it focused on a star, took dark, start looping, click on PHD to calibrate a load of pinging later & nothing. The polar alignment is good & the stars are focused. This was using PHD2 so on the next run I'll try PHD just to see if I have any more luck with it.

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Well where do I start lol

PHD recognises the camera a QHY5L-II managed to get it focused on a star, took dark, start looping, click on PHD to calibrate a load of pinging later & nothing. The polar alignment is good & the stars are focused. This was using PHD2 so on the next run I'll try PHD just to see if I have any more luck with it.

Hi

I would say PHD2 is a lot better.  It's recommended to use the ascom driver with the qhy5l-ii. Not sure what you mean by 'a load of pinging'? How many calibration steps did it do? What happens exactly?

It would help to know more details of your guiding setup.

Are you running Stellarium and Eqmod?

Louise

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Well where do I start lol

PHD recognises the camera a QHY5L-II managed to get it focused on a star, took dark, start looping, click on PHD to calibrate a load of pinging later & nothing. The polar alignment is good & the stars are focused. This was using PHD2 so on the next run I'll try PHD just to see if I have any more luck with it.

Saturated star ??

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Right I'll try to explain this as best as I can as I'm not that technically minded, I polar align the mount, I don't use Ascom simply just that I can't get my head round it so I just use the handset & use the camera & mounts guide port via the cable. I start up PHD2 which finds my camera with no issues, I set the camera exposure duration then take a dark, when I've done that I start PHD but it doesn't seem to want to calibrate. Hope that makes sense & apologies for hijacking the thread.

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Hi again

The first thing that comes to mind is that you have to select 'on camera' for the mount control. If you've done that then there could be a problem between the camera st4 and the mount - most likely a faulty cable or bad connection. I've not used st4 control so I've no experience with troubleshooting. There are manual controls in the phd2 tools. You can use them to check that phd is able to talk to the mount.

Hth

Louise

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Tich,

I'm going to assume you know nothing about guiding, so apologies if that is not the case and what is about to follow is patronising cr4p...!

You don't mention selecting a star with the green cross hairs - are you doing that? Are you actually seeing stars on the PHD screen?

When you say that you start PHD2, do a dark then start PHD - what do you mean? Are you literally starting the PHD v.1 application separate to PHD2 or do you mean that you click the PHD target icon?

As Louise says - are you setting the 'Mount' option to 'On-camera' in the drop down menu?

No problem to 'hijack' the thread - hopefully between us all we can get you guiding... It's well worth the teething pain!

Gav.

Sent from my iPhone using Tapatalk

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Ok, just read one of your earlier threads and you can happily ignore most of my last post....

Sent from my iPhone using Tapatalk

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Does PHD come up with any comment at the bottom of the screen when it's pinging....?

My guess is that it says 'star did not move enough'...?

Sent from my iPhone using Tapatalk

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LOL don't worry about it Gav I think with the lack of clear skies at SGL you got away with me not picking your brains. I'll try again next time we get a clear enough sky as all I've only ever managed is unguided stuff with limited success. I've watched a few online tutorials & they make it look so easy, a bit different when you have a go yourself though, but you're right I know pretty much nothing about guiding.

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LOL don't worry about it Gav I think with the lack of clear skies at SGL you got away with me not picking your brains. I'll try again next time we get a clear enough sky as all I've only ever managed is unguided stuff with limited success. I've watched a few online tutorials & they make it look so easy, a bit different when you have a go yourself though, but you're right I know pretty much nothing about guiding.

Hi again

You can probably check whether phd is talking to your mount, during the day. It's easier to fiddle with some things in daylight :)

Louise

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Thanks I'll have a go with it again over the weekend of possible.

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