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Phd guiding problem


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Some light reading before bed  .

 A little further on so its not been wasted tonight was more about getting it working which to some extent I have certainly more than it was .

Ok ill give some time to reading the manual as it really cold out and the wind is picking up again ill report back.regards baz

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A few remarks.

1. You have odd star shapes with a pronounced halo. How do you focus the guide scope? For good guiding, you need good focus. There used to be a recommendation to slightly defocus the guide scope, but imo, in an era of cmos cameras with small pixels, this is no longer needed. Good focus gives a better signal to noise ratio.

2. Your guide graph is all over the place. It needs to be calmed down. Start by increasing the exposure to 2 - 3 seconds to reduce the effect of seeing. Next, reduce aggression to 50 %. Make sure that your guide rate in ascom and in phd is set to 0.5. A high rate and aggression will give larger guide corrections. If most of the star movement is due to seeing, you're chasing tracking errors that don't exist, and over correct them.

3. If you have a smooth running mount and good polar alignment, then theoretically, you shouldn't need to guide in DEC. So, DEC tracking deviations can be a good indicator of seeing. On nights with poor seeing, you'd increase MinMo, which is the minimum a star needs to move before a correction is sent to the mount. On nights with good seeing, you can decrease MinMo, to benefit from the sky conditions.

4. Finally, while it is possible to reuse guide calibrations, I wouldn't do that while dialing in the best settings. It's better to calibrate too often than not often enough.

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Hi Barrie,

Need your latest GuideLog !

Stars look like you had dew on the guidescope.

Is that the best focus you could get ? 

Did you make a new Equipment Profile with the correct FL in the calculator,  and then Calibrate ?

You should also use the PHD2 Dark Frames/Bad-Pixel Map.

Michael

 

 

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1 hour ago, michael8554 said:

Hi Barrie,

Need your latest GuideLog !

Stars look like you had dew on the guidescope.

Is that the best focus you could get ? 

Did you make a new Equipment Profile with the correct FL in the calculator,  and then Calibrate ?

You should also use the PHD2 Dark Frames/Bad-Pixel Map.

Michael

 

 

Morning .

I'll get it up on here today 

As for focus no I didn't think it mattered on guide scope I've a lot to learn in this ill post up the log in a short wile .

Regards Baz 

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8 hours ago, wimvb said:

A few remarks.

1. You have odd star shapes with a pronounced halo. How do you focus the guide scope? For good guiding, you need good focus. There used to be a recommendation to slightly defocus the guide scope, but imo, in an era of cmos cameras with small pixels, this is no longer needed. Good focus gives a better signal to noise ratio.

2. Your guide graph is all over the place. It needs to be calmed down. Start by increasing the exposure to 2 - 3 seconds to reduce the effect of seeing. Next, reduce aggression to 50 %. Make sure that your guide rate in ascom and in phd is set to 0.5. A high rate and aggression will give larger guide corrections. If most of the star movement is due to seeing, you're chasing tracking errors that don't exist, and over correct them.

3. If you have a smooth running mount and good polar alignment, then theoretically, you shouldn't need to guide in DEC. So, DEC tracking deviations can be a good indicator of seeing. On nights with poor seeing, you'd increase MinMo, which is the minimum a star needs to move before a correction is sent to the mount. On nights with good seeing, you can decrease MinMo, to benefit from the sky conditions.

4. Finally, while it is possible to reuse guide calibrations, I wouldn't do that while dialing in the best settings. It's better to calibrate too often than not often enough.

The guide camera I'm using is an old Samsung scb 2000 that I converted fir guiding .

I could get the focus a lot better but like you said I read somewhere to defects to make it easier to pick up I eventually set it at 3 secs to try to stop it chasing the seeing plus it was more of an experiment to try get it to guide as before this I was completely at a loss and  could not get it to stay on a star for more than a few seconds .

It was also windy very but I rarely get the conditions (as all of us ) so wasplaying about so the wind may have been a factor as well 

I'll dial those settings in and try again tonight as the wind has dropped and it supposed to be clear  I'll also post up the log and let you guys look at it .

Again thanks for taking the time to reply guys its really appreciated. 

Regards Baz 

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Real weird one tonight no matter what I did I could not get it to calibrate nor guide it h

Just would not follow the  guide star and then it had some sort of conflict 5hat restarted my handset that my laptop controls to everytime I tried to guide it shut it off which meant restarting from scratch I'll upload the log file but it was nearly kicked around the garden had to let it be for tonight .

Regards Baz 

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Good morning. 

Is there anyway to trial a dummy test inside without any stars etc basically to test the mechanics of the mount etc .

After I stopped guiding and allowed the guiding to be done with apt dither it was ok and was getting about 90 second exposures like that .

It is an older mount that has seen some use 

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Hi Barrie

From the 28th Nov Guidelog:

Pixel scale = 25.44 arc-sec/px, Binning = 1, Focal length = 60 mm.

I'm sorry I didn't spot this earlier on, when you said your Guidescope wasn't 1000mm, but 60mm.

60mm is the aperture, not the FL, which is probably 240mm.

Not worth saying anything else about the guiding until you get your settings right.

Michael

 

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10 minutes ago, michael8554 said:

Hi Barrie

From the 28th Nov Guidelog:

Pixel scale = 25.44 arc-sec/px, Binning = 1, Focal length = 60 mm.

I'm sorry I didn't spot this earlier on, when you said your Guidescope wasn't 1000mm, but 60mm.

60mm is the aperture, not the FL, which is probably 240mm.

Not worth saying anything else about the guiding until you get your settings right.

Michael

 

Hi mate thank you. 

How did you get the pixel scale. 

My scb camera pixel size is from the info I can get are 6.35 x 7.40 microns in size 

So I read the instructions and dialed in the 7.4 .

And yep I got it wrong and your bang on the money fl is 240 mm .

So me getting these setting wrong how will this effect the guiding .

Please excuse the simple questions but I need to know the reason behind it otherwise I'd not be learning anything with  just a set of settings etc . 

If my logic is correct it would think it is looking at a part of sky which in reality would be bigger or smaller given the settings than it really is so the corrections would be a mile and a yard out (am I correct )

Again thanks for taking the time to help it is more than appreciated. 

Kindest regards Baz 

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Hi Barrie

"How did you get the pixel scale. "

A quote from the GuideLog

"So me getting these setting wrong how will this effect the guiding "

The PHD2 Calibration works out how far the mount is moving for each step-size calculated from the pixel size and focal length, in other words from the image scale / pixel scale.

Part of what it finds during the Cal is whether the mount is actually moving as far as the settings suggest, which exposes problems like Dec Backlash.

In practice PHD2 will cope with an error in the pixel scale setting, but not the huge error you introduced.

But the errors reported in the guidelog would be wrong, as they're based on a incorrect pixel scale.

Michael

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26 minutes ago, barrie greenwood said:

Hi mate .

Ok ill givevit a try with the new settings .

One last thing when I tip the scope south pointing and set the Dec at 0 .

I see in the eqmod screen that it says pier West pointing does that mean that the Weught bar should be pointing to the west or east .

Regards Baz 

Not so sure that i understand what you mean.. you don't set it at DEC 0, you point it at DEC 0( which is on the equator)

Just to clarify,  slew the scope south, click on the drift tool in phd2 and it brings up the DEC in degrees and meridian offset..slew and make sure the DEC is on 0 and as close to 0 on the meridian offset.. then close the drift tool.. just before you calibrate,  take the slack out of the DEC gear .. watch this video.. for it to make sense 20211130_190751.thumb.jpg.ed09cd69abf4f4aaae8323b0f7715924.jpg

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