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Time for a new Guidescope and camera?


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Hi, 

Last night I had some particularly shocking guiding. Its made me think whether I should invest in a better setup? Or if i'm just limited by my mount? (I know that the AVX has a bad rep for dec backlash)

Currently, I have an Orion Magnificent Mini Auto guider and 9x50 guide scope. 

I've attached a screenshot of the log viewer & the log also, as I can never make heads or tails of all the maths. If someone would be willing to dive in and see if they can, I'd be very grateful.

Is it an equipment problem? Or is it just that my PA is rubbish? Would a better setup improve things? A pole master maybe? No amount of drift aligning / guiding assistant makes any difference.

I read a PDF once about all the different graph patterns - saw tooth, stiction etc, but can never seem to improve things... just keep banging my head against the wall.

Cheers

Joe 

 

Start of the night:

452258746_ScreenShot2020-04-25at12_12_17.thumb.png.4ba79653869f76ba926a0d3224132017.png

Later on:

1135248781_ScreenShot2020-04-25at12_12_48.thumb.png.23e621cda8026dfc7737820e55bf9ee9.png

Log:

PHD2_GuideLog_2020-04-24_215344.txt

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Hi @michael8554 

Yeah that sounds about right. It’s been a long time.  My setup is permanent in my observatory. But, does this mean that it’s time for a new calibration? 
 

Before the permanent setup I used to calibrate every night i imaged. Maybe I’ve gotten a little too lax in doing that.
 

My camera and scope haven’t moved orientation in a while, so I’ve always just assumed the calibration would still be ok, but who knows? At this point I’ll try anything. 
 

Is it not the case then that observatory and permanently setup scopes should save and reuse a calibration? Or only for a few months at a time? Maybe a year is pushing it 

Cheers

Joe

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Yes on a permanent setup you can reuse the Cal for a goodly time, but seeing the Cal might help the diagnosis. 

In a permanent setup the PA shouldn't change of course, and doesn't need to be better than 5arcmins if you're guiding.

Yours is 10 arcmins, so a small one-time tweak would help, you really don't want to bother with Polemaster with a permanent setup. 

As you haven't used the mount in a long time maybe slewing it around for a while to redistribute the grease might help. 

The big evenly spaced spikes in Dec are worrying, do you have Backlash Comp set in the mount, this should be set to zero as it conflicts with the PHD2 Backlash Comp and guiding? 

Or dragging cables? 

Are you Dithering with an external prog? I can see the settling, but not the Dither command.

Also Settling is taking 2 minutes sometimes! Are your settling settings too stringent?

The frequent Star Lost messages suggest the Seeing was poor, or that your 1 sec exposure is too fast. 

And the very choppy guiding might also be a consequence, Chasing the Seeing perhaps? 

Do a new Cal at Dec 0 after nudging North to take up any backlash, run the Guide Assistant, accept the recommendations, then guide for 10 mins without altering anything, and post the log if it's not looking good. 

Michael 

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How do I get to see the cal ? I’ll post it in here... I will double check that the backlash comp isn’t on in both places. 
 

I tried Dithering in Sequence Generator Pro once. And then gave up. I’ll check it’s off. 
 

settling settings? Didn’t know there were such things. The only things I tend to change are the Hysteresis amount and minmo and guide direction. 
 

I read something the other day that mentioned bumping the exposure to 2 secs so I’m willing to give that a go. 

Its been the clearest nights here this week in months. I hope I wasn’t chasing the seeing otherwise I’ve got no chance. 
 

thanks 

Joe

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Forgot to mention the Periodic Error is about 100arcsec peak to peak, if your mount has PEC I'd give that a go.

The guidelogs are kept for 3 months, so that old guidelog from May last year with the Cal on it is way gone.

Settling - you've dithered, which has moved the mount further than normal guiding, so it will take a few seconds to stabilise the guiding at the new position.

The settling reports when the guiding has got to within a certain fraction of a pixel.

2 seconds is a typical exposure.

Michael

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Hi,

I just found these settings in SGP:

97868953_ScreenShot2020-04-26at10_56_39.png.5e3417a26ad9910c16fcc45464f5130d.png

Dithering is off, but it seems as soon as the guider reports under 0.3px then guiding will 'be considered settled' and resume immediately... Is this what you mean by too stringent? Is it better to have a few seconds in the For box to let it wait? How many is a few? Or increase/decrease the settle at value? 

There is so much maths in all of this, my head hurts.

My mount does have PEC, but I've been too scared to use it... the Celestron book isn't very clear in how to do it, it seems to suggest it needs to be run run every time I turn the mount on... (currently though, I hibernate it every night, so it keeps its alignment and time) so maybe I just run it once and as long as its only hibernated it should remember it?

Thanks

Joe

 

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5 minutes ago, alacant said:

Hi

How were your images?

Cheers

Hi,

I've not stacked them yet, 10 of them had Starlink trails in... thanks Elon. But here is a single 5 minute Luminance from the start of the run... 

1334834399_ScreenShot2020-04-26at11_15_28.thumb.png.3f19c24afb3046c27ab7480dfc7eda14.png

and here is one from the middle of the run, when the guiding was shocking:

143005956_ScreenShot2020-04-26at11_16_41.thumb.png.7256fc69973144a9642355c0db783b6f.png

Noticeable differences

Joe

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19 minutes ago, joecoyle said:

I've not stacked them yet

Hi. The satellite trails can be removed by stacking with a clipping algorithm. Are those images unacceptable for you? Don't forget that seeing conditions have a big impact on guiding. On night guiding can be wonderful. The next, all over the place, circumnstances over which you have no control. Look first at the images, then the graphs!

From bitter experience, I think that unless the mount is mechanically perfect, has been pulled apart, cleaned, regreased, and adjusted, fighting it with software is not going to bring much improvement. But hey, if the images you get are ok, just leave it!

Cheers, good luck and stay safe.

  

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5 minutes ago, alacant said:

Hi. The satellite trails can be removed by stacking with a clipping algorithm. Are those images unacceptable for you? Don't forget that seeing conditions have a big impact on guiding. On night guiding can be wonderful. The next, all over the place, circumnstances over which you have no control. Look first at the images, then the graphs!

From bitter experience, I think that unless the mount is mechanically perfect, has been pulled apart, cleaned, regreased, and adjusted, fighting it with software is not going to bring much improvement. But hey, if the images you get are ok, just leave it!

Cheers, good luck and stay safe.

  

Yeah PixInsight usually does a good job at removing the trails, I meant I just hadn't gotten around to it yet :) 

The images from early on I would say are fine (no worse than other nights), later on, they are quite egg shaped. It could have just been bad luck. I want to see if its possible to get 10 minute exposures for example, rather than sticking safe with 5.

I agree look at the images first then the graph is a good mantra, but I just want to get the graph as flat and as I can... it seems everyone else has nice flat graphs so it makes me wonder If I've messed up on the simple things along the way... 

My mount is no way near mechanically perfect nor will it ever be, I really don't fancy taking it apart, so I will have to accept certain limitations.

I've always been relatively happy with the images I get. But there's always room for improvement :)

Cheers

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27 minutes ago, joecoyle said:

wonder If I've messed up on the simple things along the way

There are so many phd2 variables that it's easy for some to get overlooked. Go back to making a new profile from scratch and starting from nothing perhaps? It's been known to cure many a problem.

 

29 minutes ago, joecoyle said:

later on, they are quite egg shaped

Maybe a change in seeing or the telescope became unbalanced or moved to a badly meshed or poorly lubricated part of the gear wheel? As I say, loadsa variables!

Cheers

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There does come a point when further fettling of the mount worm and PHD2 settings is no longer effective. 

So long as the RA and Dec RMS are similar you'll have round stars, though they my be fatter than you'd like. 

Certainly too many poor frames at the moment to give up refining. 

Is the main camera imaging during those 2 minute Settling periods, or is it paused? 

I don't know SGP, so I can only suggest setting the Dither to after every zero frames if it will let you, and try the settling to 1 pixel since nothing is going on. 

Michael 

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37 minutes ago, michael8554 said:

There does come a point when further fettling of the mount worm and PHD2 settings is no longer effective. 

So long as the RA and Dec RMS are similar you'll have round stars, though they my be fatter than you'd like. 

Certainly too many poor frames at the moment to give up refining. 

Is the main camera imaging during those 2 minute Settling periods, or is it paused? 

I don't know SGP, so I can only suggest setting the Dither to after every zero frames if it will let you, and try the settling to 1 pixel since nothing is going on. 

Michael 

More maths - I know RMS means Root Mean Square and is some calculation of something and is measured in px. What I haven't found yet is the magic number for what the value should be... RA and Dec should be X, and the total should be under Y. 

What also confuses me is PHD's guide trend lines that show PA error (in a different unit to RMS I think) when doing a drift align... sometimes I can get it really good (less than 5, sometimes 0.1) and sometimes its like 25/30. Smallest tweaks of the knobs are given to make it swing wildly and the trend lines move a lot in the opposite direction. Is that just teeth on the gears not finely tuned enough to give me that control?

I'll certainly keep refining - I agree there is more to do yet before giving up. That and I've spent far too much for this setup to be a pretty ornament in the garden. 

Yes whilst the guider is settling, the imaging camera is not taking pictures.

I will do some research into dithering and what SGP will allow for - I've always considered it too advanced for me and wanted to get the basics sorted first.

Sorry for rambling on. I know its all in the documentation somewhere.

Joe

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PHD2 shows arcsecs and pixels for the Statistics.

Pixels is how far stars have moved on the guidecam,  arcsecs is the same thing but in , erm, arcsecs, which translates to how elongated your imaged stars are in RA and Dec.

People get very excited when the Stats are showing 1 arcsec or less.

When using the PHD2 Drift Align I find it can take several minutes per measurement for the RA line to stabilise back on the x axis, up to that point the Dec and RA lines are moving relative to each other, and so is the reported PA.

A few arcmins of PA is a tiny adjustment, you may find just rotating the mount PA knobs a tiny bit without loosening anything will be enough, you'd be amazed how bendy most mounts are.

And avoids it all changing when you tighten up !

PHD2 is complicated, looked at SGP and similar, and PEMPro for PEC, but far too complicated for me.

Michael

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