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  #21  
Old 12-09-2014, 02:43 PM
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Octane (Humayun)
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Lee,

What happens when you reduce your aggressiveness down to 10%?

If you're within an arcminute of the pole (for the region of the sky in which you drift aligned), you might find that 50% at 600mm might be too much. This has certainly been the case for my FSQ/STL/G-11 combination. I've had to reduce my aggressiveness down to 1-1.5 to obtain a flat graph in MaxIm DL.

H
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  #22  
Old 12-09-2014, 03:38 PM
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An AP1600 will fix that graph
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  #23  
Old 12-09-2014, 05:28 PM
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Quote:
Originally Posted by Logieberra View Post
Do you have a cheapy guide scope handy? OAG'ing is a lovely thing, but I'd start simple. Master a separate guide scope first, play with the guiding settings and in time go back to OAG.
Good call. Wish I did... I was agonising over guide scope vs OAG for a while but decided on OAG since it was where I'll end up anyway as I'll be shooting at 1600mm very soon (hopefully). I imagine with a guide scope the issue in RA would be much less pronounced in the images thus probably enabling effective guiding. Still kind of a bandaid though.

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Originally Posted by traveller View Post
Hi Lee,
I recommend you do drift alignment using PHD first (I used my guider with my ED80). It's so much easier to do and the feedback can be very quick.
http://njstargazer.org/PolarAlignment.asp
Take your time and be patient, you will get there.
Bo
Thanks mate, I did drift align with PHD2 and apparently had it within 1 arcminute on both axes.

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Originally Posted by pluto View Post
Or even better use PHD2's built in drift alignment helper tool.
Yep, that's what I used.

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Originally Posted by Octane View Post
Lee,

What happens when you reduce your aggressiveness down to 10%?

If you're within an arcminute of the pole (for the region of the sky in which you drift aligned), you might find that 50% at 600mm might be too much. This has certainly been the case for my FSQ/STL/G-11 combination. I've had to reduce my aggressiveness down to 1-1.5 to obtain a flat graph in MaxIm DL.

H
Thanks H. My understanding of the aggressiveness setting is that it's a percentage of how much guiding should be applied relative to how much the software thinks it should apply.

The software should have established how much it should move to correct for any given error during the calibration process, so the focal length shouldn't make a difference if calibration was successful.

Based on that I would expect that having to reduce the aggressiveness so... aggressively indicates that the software has gotten it really wrong.

Speaking of calibration though, I have noticed during calibration that it completes E-W in about 15 steps, says that it's clearing backlash twice, and then completes N-S in about 7 or 8 steps which seems interesting.

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An AP1600 will fix that graph
lol I wish.
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  #24  
Old 12-09-2014, 05:35 PM
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Yes, your PHD graph is awful ! I've been "getting to know" my second hand NEQ6 over the last few months too, I feel the pain !

I reckon your polar alignment is fine, the 0.43'' RMS is typical for seeing.

RA guiding looks like the mount is not getting enough corrections, or not responding to the guide commands properly. I see about +-15'' drift in RA when not guiding, so the guiding commands do seem to be getting through eventually, since you're getting about +-3''.

In fact, on your graph there's a couple of minute periods where RA guiding is OK (probably correspond to periods when the unguided plot reaches plateaux on the the main +-15'' sine wave).

Don't suppose you have a small Max RA duration in the PHD settings limiting the corrections being sent ? If you haven't already tried, you could also set the mount auto-guide speed up to 1X, and up the aggressiveness.

I've found that 1s intervals give me best results in PHD with an ED80 and RC8 (ST4 guiding and guidescope). I don't think moving up to 5s will help control RA guiding.

You could also try guiding at say -70 to -80 declination to see if your setup can keep up with guiding there (ie when much shorter RA guide commands are needed).
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  #25  
Old 12-09-2014, 05:37 PM
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jenchris (Jennifer)
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I used my oag with an f10 for 18 months.
During that time my graphs looked awful and often my pics came out at least recognisable.
I hated the graphs so much I went over to an f5 500mm sw refractor as a guide scope
my graphs look amazing now but my pics are no better
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  #26  
Old 12-09-2014, 05:56 PM
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Next step, I suggest getting EQMOD running, and then set up the VS-PEC (this is easy to do now). Run this through 5 worm cycles of training. Then, re-test the PHD guiding with the PEC+pulse running. The form of the RA errors are such that it looks a lot like a bad PE, and so VS-PEC might well be your saviour.

By the way, are you SURE that you're using the hysteresis algorithm for RA? You see, your picture doesn't show up the RA aggr/hyst settings next to the brain (probably because the camera/mount is disconnected), but it does leave open the possibility that you accidentally turned on resist switch or lowpass for the RA guiding (this would explain a lot!).

Also, make sure to use the latest version 2.3.1c build

Last edited by Amaranthus; 12-09-2014 at 06:10 PM.
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  #27  
Old 12-09-2014, 06:13 PM
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From the look of the RA graph I'd suggest the mount is too well balanced. This causes the worm to lose contact with the gear.
Try making it a fraction "east heavy". I know that's a pain since you have to rebalance after a meridian flip but it could be your answer.
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  #28  
Old 12-09-2014, 09:15 PM
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I just use a sliding 200 gram stainless steel counterweight - Telescope on the east side, slide weight UP a few inches. Telescope on the west side, slide the weight down a few inches. It's all it needs.

I also make Dec SLIGHTLY camera heavy too.
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  #29  
Old 13-09-2014, 08:15 AM
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I couldn't get my NEQ6 pro mount running properly until I had
the Dec & RA backlash adjusted & I also fitted a better counter weight bar
as per here:

https://www.flickr.com/photos/247194...in/photostream
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  #30  
Old 13-09-2014, 11:06 AM
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Gday Lee

Did you save the log?????
If so, you can also use something like PHDLab to view the runs.
I cant see how big the drive pulses are in RA, but as they swing from positive to negative, it indicates its not just drift.
I agree that maybe the max RA duration is being exceeded,
but the graph scale appears to hide that info
This can be easily checked from the log data
ref a log from a mount that had too low a setting and when the guides cant keep up, you get the bad excursions.

Andrew
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  #31  
Old 13-09-2014, 06:22 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Lee

Did you save the log?????
If so, you can also use something like PHDLab to view the runs.
I cant see how big the drive pulses are in RA, but as they swing from positive to negative, it indicates its not just drift.
I agree that maybe the max RA duration is being exceeded,
but the graph scale appears to hide that info
This can be easily checked from the log data
ref a log from a mount that had too low a setting and when the guides cant keep up, you get the bad excursions.
Andrew, I'd expect if the max duration was insufficient that once guiding stabilised the corrections would always be in the same direction and the plot would drift off the top or bottom of the graph.

The PHD2 guys might consider having a warning popup if it wants to exceed the duration limit often and in the same direction. I'll ask them.
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  #32  
Old 13-09-2014, 09:15 PM
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Gday Andrew

Quote:
I'd expect if the max duration was insufficient that once guiding stabilised the corrections would always be in the same direction and the plot would drift off the top or bottom of the graph.
Dont understand here, why would it drift off the graph????
The plot came from a mount that uses belt drives all the way to the final axis. It has very large but very smooth PE.
When the PE "rate" was small, it guided OK, but when the PE "rate" was changing at its maximum level, it couldn't keep up, hence the star drifted, but was still "locked" onto. ie PHD2 still knew it needed to bring it back.
On the PE "rate" slowing down then reversing, the guiding managed to incrementally catch up and the plot came back to centre and guiding once again worked for a while, then cr@pped out again later.

ie PHD2 can set a max "pulse time". This creates an absolute limit on how much error can be accounted for "timewise" in a given frame.
The scopes guide rate and PHDs aggressiveness, hysteresis and all the you beaut algorithms etc are all irrelevant if at the end of the day, they calculate a pulse time required that is greater than is allowed by the max pulse time.
I fully agree PHD2 should provide a warning if the max pulse time is hit for more than say 2 consecutive guides.

Andrew
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  #33  
Old 14-09-2014, 04:10 PM
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Thanks everyone for your help! :-)

I'll try to cover off on all the questions you have asked:

* Definitely using hysteresis algorithm for RA
* Max guide pulse on RA has been set to 400 for that chart. It was at 1000 I think, maybe 1200, but that was causing it to constantly be correcting in alternate directions (and I ended up with square stars) so I dropped it thinking that was too much
* I didn't save a log.. I thought I checked that option but when I went to retrieve the log it wasn't there
* Already using EQMOD, definitely going to look into PEC... how long does that take? I understand you should do it each time you change anything (including balance, I assume), so it seems like it should be more or less part of the daily set up

I tried shifting the RA axis by hand today... if there was a backlash problem should I be able to feel anything? Feels very smooth in both directions.

The chart really would make sense if it was a backlash / balance problem. I've tried balancing in all directions, but I haven't been particularly precise about it, other than having tried "perfect", east heavy to an arbitrary degree and the same for west... maybe there's a sweet spot that I've missed.
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  #34  
Old 14-09-2014, 05:29 PM
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Quote:
Originally Posted by codemonkey View Post
Thanks everyone for your help! :-)


I tried shifting the RA axis by hand today... if there was a backlash problem should I be able to feel anything? Feels very smooth in both directions.
lock the clutches to stop the thing from moving, put on a scope and then see if you can feel any slight rocking (a sort of "clonking" feel) as you try to move the RA by pushing/pulling gently on the end of the scope. If there is any noticeable back-forth movement at all with the clutches locked, you have backlash. You need a very small amount to stop the gears from binding, but if you can feel some slop, it is too much and it would be worth tightening the worm up a bit.

If the backlash is OK, it would be worth checking that there is not too much preload on the RA bearings - which would make the movement a bit stiff - smooth, but a bit sticky to get moving. The last dozen or so panels in http://www.astro-baby.com/EQ6%20rebu...%20rebuild.htm show what you need to do to check that - just take off the polar scope surround, loosen the grub screws and rotate the nut to tighten/loosen the axis bearings. Tighten the bearing nut until you can just feel that the rotation is stiffer and then back off the nut until the rotation frees right up. Then redo the grub screws and replace the surround.

Last edited by Shiraz; 14-09-2014 at 06:01 PM.
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  #35  
Old 14-09-2014, 10:51 PM
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Quote:
Originally Posted by AndrewJ View Post
I fully agree PHD2 should provide a warning if the max pulse time is hit for more than say 2 consecutive guides.
For those who don't follow the Open PHD Guiding Google group the max duration warning should show up sometime soon. Andy agreed it was a good idea and posted a draft of how it would look a few hours ago.
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  #36  
Old 15-09-2014, 05:41 PM
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Quote:
Originally Posted by Shiraz View Post
lock the clutches to stop the thing from moving, put on a scope and then see if you can feel any slight rocking (a sort of "clonking" feel) as you try to move the RA by pushing/pulling gently on the end of the scope. If there is any noticeable back-forth movement at all with the clutches locked, you have backlash. You need a very small amount to stop the gears from binding, but if you can feel some slop, it is too much and it would be worth tightening the worm up a bit.

If the backlash is OK, it would be worth checking that there is not too much preload on the RA bearings - which would make the movement a bit stiff - smooth, but a bit sticky to get moving. The last dozen or so panels in http://www.astro-baby.com/EQ6%20rebu...%20rebuild.htm show what you need to do to check that - just take off the polar scope surround, loosen the grub screws and rotate the nut to tighten/loosen the axis bearings. Tighten the bearing nut until you can just feel that the rotation is stiffer and then back off the nut until the rotation frees right up. Then redo the grub screws and replace the surround.
Thanks mate :-)

Checked the backlash and couldn't notice any movement, certainly no clunking back and forth. Looks like the next step down this path requires opening 'er up... not sure I'm game just yet, I'll see how I go.

I'll have one more crack in the next couple of days I think, try a couple of long shots and if that fails then I might have to open her up.

Thanks again!
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  #37  
Old 15-09-2014, 05:55 PM
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I'd try VS-PEC first. A simple fix it if works. It takes about 45 min to go through 5 worm cycles of training, but you can choose anywhere from 1-5 depending on the robustness of the final function you're willing to accept. You can have this running whilst you are imaging except if you are dithering.

Since you are using EQMOD already, it will be easy to do this. It's literally a 1-button operation -- nicely called 'AutoPEC'. Try it!
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  #38  
Old 15-09-2014, 06:03 PM
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Originally Posted by Amaranthus View Post
I'd try VS-PEC first. A simple fix it if works. It takes about 45 min to go through 5 worm cycles of training, but you can choose anywhere from 1-5 depending on the robustness of the final function you're willing to accept. You can have this running whilst you are imaging except if you are dithering.

Since you are using EQMOD already, it will be easy to do this. It's literally a 1-button operation -- nicely called 'AutoPEC'. Try it!
Ah yeah, forgot about that, thanks for the reminder
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  #39  
Old 15-09-2014, 09:06 PM
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Gday Andrew

Quote:
For those who don't follow the Open PHD Guiding Google group the max duration warning should show up sometime soon.
As you are a member there, just another thought re warnings.
The mount i got the earlier plot from had a lot of underlying drift as well as very large PE ( even tho it was smooth ).
In some of the runs we grabbed, the "unguided" data for DEC looked horrible, but the error was semi masked when it was guided.
I traced this back to ( very ) bad calibration data, and what appears to be the way PHD converts between sensor and sky coordinates.
I see PHD2 calculates 2 calibration angles to convert the sensor X,Y into RA/DEC.
These should always be 90deg apart ( ie X to RA and X to DEC ), but in some cases we got ( IIRC) up to 90+/-35deg difference between them.
PHD then converted the data using the 2 separate angles and as such both the displayed data and sent pulses were wrong as the RA PEC was contaminating DEC data.
Not saying thats the case here, but it is another possible cause for oddball guiding.
I have no idea why PHD2 uses 2 discrete angles, as there is no way to properly measure the DEC angle due to the PE in the RA drive????


Andrew
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  #40  
Old 15-09-2014, 11:20 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Andrew
As you are a member there, just another thought re warnings.
The mount i got the earlier plot from had a lot of underlying drift as well as very large PE ( even tho it was smooth ).
In some of the runs we grabbed, the "unguided" data for DEC looked horrible, but the error was semi masked when it was guided.
I traced this back to ( very ) bad calibration data, and what appears to be the way PHD converts between sensor and sky coordinates.
I see PHD2 calculates 2 calibration angles to convert the sensor X,Y into RA/DEC.
These should always be 90deg apart ( ie X to RA and X to DEC ), but in some cases we got ( IIRC) up to 90+/-35deg difference between them.
PHD then converted the data using the 2 separate angles and as such both the displayed data and sent pulses were wrong as the RA PEC was contaminating DEC data.
Not saying thats the case here, but it is another possible cause for oddball guiding.
I have no idea why PHD2 uses 2 discrete angles, as there is no way to properly measure the DEC angle due to the PE in the RA drive????
Andrew, I think you'd do better asking Andy Glasso this one. (Yes another Andrew.) Either join the group (https://groups.google.com "open phd guiding") and send the debug and guide logs, or if you want to avoid that send me the logs and I'll submit your question.

If you are using ASCOM to do pulse guiding PHD2 is supposed to get the current RA and Dec from the mount and use the Dec to recalculate the pulse lengths as you change position.
If you are using ST-4 the recent versions can use "On camera" for guiding and have an "Aux mount" connection to get the mount position. I haven't had a change to try this yet.
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