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PHD2 guiding and tracking errors. Help !!!


johngm

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Hi fellow stargazers,

I hope someone can help me with my problem. 

First, the equipment I'm using.

Skywatcher ED80, celestron CGEM with starsense, Modified Canon 600D, 60mm Guidescope with ASI120M guide camera.

On Monday, I managed to get out and image the rosette nebula, after getting my camera back from modifying at Astronomiser (a big thanks to Andy Ellis). I got a total of 30 x 3min subs ISO 400 (with cls clip in light pollution filter)Autosave_Windows.thumb.jpg.54a1e13058c39a32c7d6b23994ffab66.jpg

 

I have only done a basic stretch. But I wanted to get another 4hrs LRGB data, and 4hrs Ha data, so, tonight, i finaly got some clear sky's in Tamworth, and off I went, and set up all my equipment as I have always done. levelled and Balanced the Scope, polar aligned with polemaster and done my auto align routine. Sent the scope to the target, and there it was, bang in the middle. I set up PHD2, and while it was calibrating, the stars were moving out of range. 

PHD_Screengrab.thumb.jpg.1b583e4942c01042ba57da59f0fa66ec.jpg

 

I set the scale at Y +/-16, but it went off the scale after calibrating !!. I could actually see the stars moving across the display. I have done all kinds of checks. I re-checked polar alignment with polemaster and sharpcap, I even sent it to the target and polar aligned in that position to eliminate any kind of flexure in the mount. According to sharcap, my polar alignment was within 0.30" arc minutes, so, I eliminated that. I reset PHD2 just incase I had accidently altered any parameters. I tried altering the balance, choosing targets in all directions to eliminate balance issues. After many trials and errors and hair pulling, I did a test. First, I Slewed to a region just above Orion (which was now past the meridian) and took 3 x 1min exposures unguided. Then I took 3 X 1min guided exposures. All with the same result. 1 of each below :

 

Unguided

5a8615da4033c_LIGHT_60s_1600iso_10c_20180215-21h22m57s532ms.thumb.jpg.4c379d9071c8f61b1d724d5317b899e0.jpg

 

Guided

5a86162fe99d5_LIGHT_60s_1600iso_9c_20180215-21h35m45s017ms.thumb.jpg.61c41b2eae3469d0cd113004b8053491.jpg

 

All 3 images were the same for guided/unguided. What I noticed, when calibrating in PHD, was when I auto selected guide star and began calibrating, It pulsed west, as it should do, but then changed to east calibration, as it should do, but continued west with a vengeance ?. and failed calibaration. 

Has any of you come across this before ? I'm at my wits end. I'm just hoping it isn't a mount strip down job.

Regards John

 

 

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Actually, its the same power supply I have always used. What I didn't mention, I only added the starsense today, so you could have a very good valid point !. I don't know what current the starsense pulls, but I do have a 12v 10amp supply from my old LXD75. I will dig it out, or a trip to Maplins tomorrow. Thanks, you could be on to something. It does seem strange that this has only been happening since I added starsense. Thanks for that.

John

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I believe that PHD2 thinks for some reason that image scale is different than it is. Either it is that or PHD2 thinks that it is issuing correct pulse but in reality pulse is way too large.

How did you set it up? Camera parameters (pixel size), guide scope parameters (focal length). How do you guide? Is it Ascom driver + pulse guide or is it ST4?

What is your guide rate? Is your DEC setup properly for calibration and guide? (in case of ST4 guiding you need to enter it manually I think).

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I had similar issues the other night. For some reason EQMOD would just randomly stop sidereal movement but PHD would continue to try and track. I too could see the stars move across the PHD window. i had to keep checking the EQMOD tab for sidereal was ticked. I have different kit to you but I agree with spillage above that maybe a power down of everything and restart may sort it.

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9 minutes ago, vlaiv said:

I believe that PHD2 thinks for some reason that image scale is different than it is. Either it is that or PHD2 thinks that it is issuing correct pulse but in reality pulse is way too large.

How did you set it up? Camera parameters (pixel size), guide scope parameters (focal length). How do you guide? Is it Ascom driver + pulse guide or is it ST4?

What is your guide rate? Is your DEC setup properly for calibration and guide? (in case of ST4 guiding you need to enter it manually I think).

Yes, all parameters were correct. I use ST4 guiding, but like I said, it was fine on Monday.

 

31 minutes ago, Kropster said:

Stab in the dark.....Is the mount power supply ok?

Like I said, you could well be on to something Kropster. I have just checked, its a 5amp. I think I will take a trip to maplins tomorrow and get a 10amp. adding the starsencse may have just tipped it over. Makes sense that it was OK before that. Ill keep you posted.

John

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22 minutes ago, spillage said:

I have this from time to time. I just disable phd, apt, and power down the mount and start again. It seems to sort it. I just put it down to the usual gremlins.

Hi Spillage, I did try this several time to no avail.

John

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42 minutes ago, Thalestris24 said:

Hi

Looks to me like your guide camera st4 guide output is messed up. Is the cam set to 8 bit? I think this is necessary for ST4 operation. Maybe also check your ST4 cable. I think  it's  unlikely to be power since your unguided sub wasn't too bad.

Louise

Hi Louise, and thank you. The thing is, it was fine until I added starsense. My settings were exactly the same as they were Monday, when it was guiding fine. it is definitely a headache. I just done a 90s and 120s unguided test before I put my stuff away, and you can just see trailing starting at 90s. This shouldn't be happening with good PA, (according to sharpcap 0.30") I would have expected at least a good 2 mins unguided, which I normally achieve. It is rather strange.

I also disconnected starsense in the last 2 test when I was in position, but still not good. I do have a 6 amp power supply floating around somewhere from my old LXD75 mount I could try, but now after disconnecting starsense, and still having the issue, I am even more confused !!

The ST4 cable I suppose is one avenue to explore, I have the camera set to asi120m in PHD2 and, on camera guiding, and 3.75, which is correct for the ASI. But like I said, these are the same settings as Monday, when it ran OK.

John

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Hi John

Is the guide cam definitely set to 8 bit? I assume the mount is set to 'on camera'. Just looking at the shape of the phd2 graph shows a divergence between RA and DEC. The guide cam is capable of outputting 12 bit image data but I think it has to be set to 8 bit because the other 4 bits are used for the +/- RA and +/- DEC guide signals (this is what happens with the qhy5l-ii which uses the same sensor).

Louise

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3 hours ago, kens said:

It looks more like an electro-mechanical issue to me than a guiding issue. But post the guide log and I'll see if it gives any clues to whats going on.

I concur Ken, I have been sleeping on this, and what I will try before I start tonight (yes, 2 clear nights on the trot in the UK, miracles do happen) is pugging in my 6 amp power supply, if I can remember where it is, and I will guide via the HC/ascom instead of the ST4 port with another RJ12 cable as Louise suggested, just incase there is an electrical issue with the cable or port. If this cures the problem, I will take backward steps then to get to the bottom of it, after imaging NGC2237, because after 10pm, It disappears over the roof of my house, and I want to get as much integration as I can, as it will probably be another 1 month with the weather in the UK before I can do that !!!. 

Regarding the Guide log, if its still happening, I will post that by all means Ken. 

John

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Hi All, 

Just a quick update.

I nipped outside to the mount, and done a "slop" test on the RA / DEC shafts. I removed the counterweight from the Bar, and did the side to side movement check. Holding the bottom of the counterweight shaft, and moving from side to side, I had around 1 - 2mm of play, which it was last time I checked, and within parameters of what is stated should be as not to cause binding or excessive PE. Same with the DEC. So that was one mechanical check I tried without a strip down.

John

 

 

 

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7 minutes ago, Skipper Billy said:

You weren't trying to guide on a hot pixel were you ??

Done that - been there !!

Actually Billy, Hmmm, I'm wondering ??. Well, I am using auto select guide star, but on the other hand, its selecting a star in different areas of the view. Unless I have a couple of hot pixels. I suppose its worth Manually selecting star, only takes a second to check. it does seem strange when it switches from calibrate west to calibrate east, it continues west ? or, as Louise and Ken have suggested, maybe electrical issue (dodgy cable or port).

Thanks

John

 

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23 minutes ago, Skipper Billy said:

You weren't trying to guide on a hot pixel were you ??

Done that - been there !!

Actually Billy, ive been pondering more on what you said, and I then kept thinking back to the Guided / unguided 1min exposures I took at the start of the post. Were you getting the same thing happening ?

John

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7 hours ago, kens said:

It looks more like an electro-mechanical issue to me than a guiding issue. But post the guide log and I'll see if it gives any clues to whats going on.

Hi Ken, I have attached a guide log from last night for you and anyone else to check over. As you can see from the calibration steps, it was calibrating east but still going west. Could Billy be onto something when he suggested it was selecting a hot pixel instead of a star ?. The only thing amiss with my setup is 162mm focal length input for my skywatcher 9X50 finder guider. Since digging around this morning, I seen in another post that it should be set to 180mm. This still doesn't explain the fact that it was guiding fine on Monday with those settings. I have Found my 6 amp power supply, so at least I can eliminate that part of it, plus going via HC/Ascom instead of on camera.

JohnPHD2_GuideLog_2018-02-15_190321.zip

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Looking at the PHD2 screen pic - I can't see a guide star! It says snr of 26.8 - much too low. However, maybe by the time you took the screen image the mount had moved a lot. Also, the 0.5s exposure is much too short anyway - aim for 2s-ish. I suspect the problem will go away if you pulse guide rather than using the ST4.

Louise

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1 minute ago, Thalestris24 said:

Looking at the PHD2 screen pic - I can't see a guide star! It says snr of 26.8 - much too low. However, maybe by the time you took the screen image the mount had moved a lot. Also, the 0.5s exposure is much too short anyway - aim for 2s-ish. I suspect the problem will go away if you pulse guide rather than using the ST4.

Louise

Exactly right Louise, the mount would have moved quite a bit. There were plenty of stars in the FOV when I started. I will take your advice and set exposure to around 2. As regarding what you said about about pulse guiding, that was on my to do list. Also checking that its not selecting a hot pixel, although I did a reset and added a New Dark at one point, but it is another avenue to explore. I have Just looked in PHD2, how do you manually select guide star ?

John

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2 hours ago, johngm said:

Actually Billy, ive been pondering more on what you said, and I then kept thinking back to the Guided / unguided 1min exposures I took at the start of the post. Were you getting the same thing happening ?

John

As I've said that I've done this and worn the t shirt..amazing how a hot pixel or noise looks like a star..the only way I've found is to make sure your guide camera is focused..i use sharpcap as it's quicker to adjust the exposure/gain and then focus.When I used a skywatcher finder/guider I needed more inward focus so I just jammed the adapter in,obviously other cameras might be different focal point..you're quite correct that the focal length of a 9x50 skywatcher is 180mm but don't think it would be enough to cause many problems..

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15 minutes ago, nigelg said:

 

Hi Nigel

When I started off, NGC 2237 was south Easterly direction, so not to close. Also, I tried in various parts of the sky from east to west, all with the same result.

John 

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3 minutes ago, newbie alert said:

As I've said that I've done this and worn the t shirt..amazing how a hot pixel or noise looks like a star..the only way I've found is to make sure your guide camera is focused..i use sharpcap as it's quicker to adjust the exposure/gain and then focus.When I used a skywatcher finder/guider I needed more inward focus so I just jammed the adapter in,obviously other cameras might be different focal point..you're quite correct that the focal length of a 9x50 skywatcher is 180mm but don't think it would be enough to cause many problems..

Yes Newbie, I think it was your post I read regarding the focal length. But like you said, I doubt it would make a significant difference. As for the focus, its spot on with pin point stars in the FOV, and its locked down with the locking collar. I was guiding fine with it Monday.

John

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