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Strange PHD graph

JohnSadlerAstro

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ian_bird

ian_bird

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Your first post looks like a classic DEC bounce to me. Are you imaging near the Zenith (i.e. straight up)?

Try setting PHD to guide DEC only in one direction. If it zooms off screen - change it to only guide in the other direction.

Having said that - there are some really good PHD experts on SGL - so best wait for them to give some good advice. :icon_biggrin:

Cheers

Ian

 

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souls33k3r

souls33k3r

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Are you using a hub? Is it powered or USB connection? See if a direct connection of your guide cable to your machine makes any difference. Is your tripod and mount level? How good is your Polar alignment? Is your scope perfectly balanced in both RA and Dec? Try calibrating at Dec 0 and closer (East Side) of the meridian. 

Last night was my first time in the world of PHD as well. To begin with, I had a wonky graph. I started to play with Aggression, Hysterisis and MinMo... That made subtle difference to my graph but not to my liking. Then I tried "Guiding assistant", ran it for 2 min which gave me recommended values based on the last nights seeing and my mount behaviour. Guiding was better and liveable after that. Though it was very windy but my subs came out good. 

Hope this helps.  

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david_taurus83

david_taurus83

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Hi there. I too have just started with a guiding setup. ZWO ASI 120mm in a finder guider. First clear night last night for 2 weeks and I had a nightmare! Setup my EQ5 mount, aligned main scope and finder guider and used Sharpcap to do polar alignment. Worked great, no problems! Then I moved my laptop indoors, 10m from the mount. I naively bought some 5m USB extension leads and doubled them up. EQMOD worked absolutely fine for the mount along with Stellarium Scope. Both ZWO camera and DSLR were another matter. APT kept crashing and PHD2 kept connecting/disconnecting from the camera. I gave up frustrated at 1am! Apparently there's a maximum length you can use for USB leads. For lengths of 5+ metres there is something called an Active USB which is supposed to boost the signal. I am going to have to try again with laptop outside and single USB leads from each device to try and troubleshoot. I also used an old Belkin USB hub (8 years old) so unsure if this was an issue. You might be worth trying without the extension cables as well if youve bought cheap eBay ones like myself!

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JohnSadlerAstro

JohnSadlerAstro

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Hi,

I was imaging M81 and 82 last night, which were almost directly overhead. The USB cables I was using were about 20m long, (to go through our letter-box and into our dining room, I don't like standing in the cold at 3 am ;)). 

I re-ran the calibration process with the scope pointing at around +7 dec, and it seemed to work ok, but there were still very strange RA behaviours, with the guiding graph looking like a series of RA hills ending in vertical cliff-edges. After a while, though, the guiding seemed to settle down a bit; about 60% of my subs were useable (I think there was a bit of a breeze). 

I was running an EQ5 with dual-axis drives with 130 PDS. I aligned using the polar scope (I was trying using SharpCap to align, but then realized I needed to buy a license in order to unlock the last step of the PA feature--I may do that at some point). My guidescope is a standard 50mm finer, its quite small but as I'm using a DSLR and a short focal length scope there doesn't *seem* to be an issue with that.

EDIT-- Is the SharpCap PA tool worth spending the £10 for pro license with the kit ive got?

Is this what you were meaning? Also, how do I find the Guiding Log?

image.png.feb402b13e6dcc162b39def592274a12.png
 

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alacant

alacant

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29 minutes ago, JohnSadlerAstro said:

My guidescope is a standard 50mm finer

Hi. You need to enter the focal length rather than the aperture.

 

32 minutes ago, JohnSadlerAstro said:

how do I find the Guiding Log?

Try:

\Documents\PHD2

30 minutes ago, JohnSadlerAstro said:

Is the SharpCap PA tool worth spending the £10 for pro

There three PA alignment tools built into PHD2, one of them similar to the SharpCap adjuster.

HTH.

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alexbb

alexbb

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I thought from the second post that you didn't configure properly the guider focal length / pixel size.
The 50mm finder has 180mm focal length.

In the first post it seems that you have DEC backlash and you're not even issuing any RA correction movements. You have to fill the correct pixel size and focal length and if you don't have enough correction, lower the min star motion on RA and DEC.

If you see erratic movements in RA, it can be a sign of improper balance. Leave it just a bit East heavy.

For DEC, you can guide in only one direction. North or South, you will find out very fast in which direction it drifts. You can also balance a little camera heavy to help you minimize the DEC backlash effects.

 

If you filled the pixel size ok or if it was automatically retrieved by PHD, the 180mm/55mm focal length ratio is ~3.3. Divide your total RMS ~6" guiding error and you get less than 2" RMS. That should be about right for the average seeing and an EQ5.

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ian_bird

ian_bird

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32 minutes ago, JohnSadlerAstro said:

 

I was imaging M81 and 82 last night, which were almost directly overhead.

This would tend to confirm the DEC Bounce hypothesis (Backlash in DEC). As mentioned, try guiding DEC in only one direction.

Was the mount set East heavy? The RA could also be down to backlash. Setting the mount East heavy would help.

Cheers

Ian

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alexbb

alexbb

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1 minute ago, JohnSadlerAstro said:

AH!! That must be part of the trouble! I thought I remembered it being 55mm focal length; so therefore all the commands PHD was giving were waaay to harsh. :) 

Since PHD did a calibration, no, the commands should have been ok. Only the guide star movement conversion from px to arc seconds was wrong and the graphics showed more error than it was actually. I believe the mount guided as expected. 1.5-2" RMS.

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JohnSadlerAstro

JohnSadlerAstro

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Just now, moise212 said:

Since PHD did a calibration, no, the commands should have been ok. Only the guide star movement conversion from px to arc seconds was wrong and the graphics showed more error than it was actually. I believe the mount guided as expected. 1.5-2" RMS.

So am i right in understanding that PHD "thought" that each pixel was covering more sky than it actually was, therefore giving horrifying accuracy results when they were converted to arc seconds?

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ChrisEll

ChrisEll

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37 minutes ago, JohnSadlerAstro said:

Hi,

I was imaging M81 and 82 last night, which were almost directly overhead. The USB cables I was using were about 20m long, (to go through our letter-box and into our dining room, I don't like standing in the cold at 3 am ;)). 

I re-ran the calibration process with the scope pointing at around +7 dec, and it seemed to work ok, but there were still very strange RA behaviours, with the guiding graph looking like a series of RA hills ending in vertical cliff-edges. After a while, though, the guiding seemed to settle down a bit; about 60% of my subs were useable (I think there was a bit of a breeze). 

I was running an EQ5 with dual-axis drives with 130 PDS. I aligned using the polar scope (I was trying using SharpCap to align, but then realized I needed to buy a license in order to unlock the last step of the PA feature--I may do that at some point). My guidescope is a standard 50mm finer, its quite small but as I'm using a DSLR and a short focal length scope there doesn't *seem* to be an issue with that.

EDIT-- Is the SharpCap PA tool worth spending the £10 for pro license with the kit ive got?

Is this what you were meaning? Also, how do I find the Guiding Log?

image.png.feb402b13e6dcc162b39def592274a12.png
 

That calibration is not too hot! Be sure to visit the Calibration Calculator before you calibrate - this tells PHD2 to use the correct step size for your Dec and eqpt. Your focal length is off... that looks like aperture. Your RA/Dec guide speeds are not being read from the mount correctly. 

Try using a USB repeater cable if you need an extension lead.

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alexbb

alexbb

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3 minutes ago, JohnSadlerAstro said:

So am i right in understanding that PHD "thought" that each pixel was covering more sky than it actually was, therefore giving horrifying accuracy results when they were converted to arc seconds?

Yes

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Thalestris24

Thalestris24

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Hi

Using ST4 is ok but maybe a bit limiting though I appreciate you're trying to remote control from a distance. I believe using ST4 means you have to re-calibrate PHD2 if you go to a different part of the sky to image. Probably your graph reflects pointing upward which is probably what's causing the RA sine curve! I think 'east heavy' might help. PHD2 provides a easy-to-use tool for drift aligning but I think it only works with pulse guiding, not ST4 since the latter doesn't provide any scope pointing info back to you PC - it just allows guiding corrections to be sent from the camera to your mount. 

Louise

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