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Old 11-09-2014, 09:36 PM
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codemonkey (Lee)
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Worst PHD graph in history? Need help :-(

Fairly recently I bought a second-hand NEQ6 Pro, and almost simultaneously my first guide cam and an OAG. I've been unable to get guiding to work properly, in fact it just seems to be getting worse if anything.

I was starting to think it was just really bad seeing that was the cause, because with guiding disabled I can see the star move around a fair amount with almost every frame, but the problem exists almost purely in RA, no matter where I seem to point the mount, so I doubt that it's got anything to do with seeing at all.

Has anyone got any suggestions? I've been tweaking this for weeks and I'm spinning my wheels losing my remaining hair.

I've tried the obvious things like balance, checking for cable drag, boosting the exposure (5s in these), reducing the RA guide aggressiveness as far as 50%, upping the minimum move in RA as high as 1px and as low as 0.15px

I've noticed the mount seems to make a kind of "gritty" noise in DEC when slewing, mostly at the start and the finish, but the RA sounds fine...
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Last edited by codemonkey; 11-09-2014 at 09:50 PM.
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  #2  
Old 11-09-2014, 10:14 PM
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LewisM
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Polar alignment probably way off - seems to be TRYING/fighting, but losing. I had the same issue with an NEQ6 - I would rough align with a compass - and the NEQ6 has enough EM interference that the compass was out 15 or more! There is more ferrous material in an NEQ6 head than I realised.

Also,having oblate stars in the guide image isn't helping you, because PHD and most guide software looks for a centroid position of a circular light mass/pixels. Having weird shapes is NOT helping this at all. The guidescope I assume is a mini-guider, because I also used to get this with the Orion miniguider - just loosen the objective a LITTLE, (releasing the "pinch") and it should improve dramatically. Mine ALWAYS did.
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Old 11-09-2014, 10:18 PM
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LewisM
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Also, try PHD1 instead of 2. I find it works a LOT better with my setup than 2 (which almost always never even tries to calibrate!). PHD1 just locks and stays locked for me (PA down to below minute of error)
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Old 11-09-2014, 10:21 PM
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codemonkey (Lee)
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I drift aligned for quite a while on both axis before recording that. PHD was recording my polar alignment as being within 1 arcminute, so even though I don't particularly trust it, I doubt it's way off.

I spent about an hour tonight trying to get the stars a more normal shape, but haven't been able to; this was as close to round as I could get it. I'm using the Orion Deluxe OAG with a QHY5L-II, which don't really play well together because if your camera has a 1.25" you have to stick the camera into the OAG, hold it perfectly straight and then tighten a tiny screw with an allen key to lock it all up. PITA.
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Old 11-09-2014, 10:21 PM
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my guess would be that it's backlash in RA - DEC looks good.

have you tried tightening up the worm clearance as a first step. The transfer gear clearance may need to be tightened up if the worm clearance is OK. easy to check if there is a backlash problem by seeing how much the scope can be rocked in RA by hand - if you can feel it clonking back and forth, then it needs tightening. You could also try deliberately unbalancing the scope in RA so that the worm always sits on one side of the gear, but it is still a good idea to tweak up the backlash.

these mounts make strange noises when starting and stopping a slew. You can make them less noisy with careful adjustment, but it does not seem to make much difference to performance. However, the Dec noise you describe could possibly be due to a slightly over-tightened worm, so it would probably be worth checking that as well.

persevere - these are good mounts, but they require adjustments every few months to keep them in peak condition.

Last edited by Shiraz; 11-09-2014 at 10:36 PM.
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  #6  
Old 11-09-2014, 10:24 PM
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Actually, the dec graph isn't too bad, and it doesn't look like it's working very hard so your polar alignment is good enough. There's definitely something wrong with the RA though.
What focal length are you imaging/guiding at?
Cheers,
Andrew.
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Old 11-09-2014, 10:28 PM
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Quote:
Originally Posted by Shiraz View Post
my guess would be that it's backlash in RA - DEC looks good.

have you tried tightening up the worm clearance as a first step. The transfer gear clearance may need to be tightened up if the worm clearance is OK. easy to check if there is a problem by seeing how much the scope can be rocked in RA by hand.

these mounts make strange noises when starting and stopping a slew. You can make them less noisy with careful adjustment, but it does not seem to make much difference to performance. However, the Dec noise you describe could possibly be due to a slightly over-tightened worm, so it would probably be worth tidying that up as well.

persevere - these are good mounts, but they require adjustments every few months to keep them in peak condition.
Thanks mate :-)

To be honest I don't know what you mean by "worm clearance." I take it I should basically pull this apart and follow some of the video instructions I've seen on adjusting the gears to remove any play and giving them a good clean?

Quote:
Originally Posted by alocky View Post
Actually, the dec graph isn't too bad, and it doesn't look like it's working very hard so your polar alignment is good enough. There's definitely something wrong with the RA though.
What focal length are you imaging/guiding at?
Cheers,
Andrew.
Thanks Andrew :-)

This is only at 600mm... I've also bought a new scope that I haven't had a chance to use yet, an RC8... I shudder to think what the graph would look like on the RC8!
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Old 11-09-2014, 10:51 PM
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Yes, actually Dec is not too bad. I stand corrected.

Check RA spur gear tolerances. Replace the factory grease. Remove any detritus that has stuck in/on the grease. Backlash in Dec was always a major issue for me, until I cleaned, polished, re-meshed the tolerances.
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  #9  
Old 11-09-2014, 10:57 PM
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Your guide star looks horrible. I'm not surprised PHD is having trouble guiding. Are you trying to guide on a waaay off axis star? I haven't used my OAG for years but star quality wasn't it's strong point.
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Old 11-09-2014, 10:58 PM
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Quote:
Originally Posted by codemonkey View Post
Thanks mate :-)

To be honest I don't know what you mean by "worm clearance." I take it I should basically pull this apart and follow some of the video instructions I've seen on adjusting the gears to remove any play and giving them a good clean?


No, you certainly don't need to take it to bits - only do that as a last resort. There are some hex head bolts that lock the worm carrier to the main body. You undo them very slightly so that the worm carrier can slide on the body and then use the small opposing screws to wind the carrier in or out to adjust the clearance. Then tighten the main bolts back up. takes about a minute when you get the hang of it. It is a normal part of owning an EQ6 - they are even supplied with the key wrenches to do it.

This shows you how and explains what the process does (you should not need to do the end float adjustment on the worm bearings though)
http://www.astro-baby.com/EQ6%20rebu...0alignment.htm

others have commented on the guide star image quality. I have found that the centroid calculation in phd is quite OK with images like yours - it seems to be doing well in DEC in your case and I doubt that there will be any problem in RA. However, it is worth choosing an unsaturated star, rather than one with obvious saturation like the one in your example.

Last edited by Shiraz; 11-09-2014 at 11:29 PM.
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  #11  
Old 11-09-2014, 10:58 PM
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Honestly, I assume you are using an OAG due to the star shapes. I would take an image and see how it comes out, if star shapes are less than ideal then look into it. My graphs are regularly like this (in arc seconds) and I have no issues with my images.
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Old 11-09-2014, 10:59 PM
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Quote:
Originally Posted by cometcatcher View Post
Your guide star looks horrible. I'm not surprised PHD is having trouble guiding. Are you trying to guide on a waaay off axis star? I haven't used my OAG for years but star quality wasn't it's strong point.

It dosent matter what shape it is to guide on
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Old 11-09-2014, 11:15 PM
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Lee mentioned that he was using an OAG. As others noted, star shape is not critical - the centroid is based on an assumed not characterized star shape.

I'd strongly advise you try, as a first step, to increase the Westerly bias on the mount. This can really help in keeping the gears engaged. It should NOT be perfectly balanced!

PHD and PHD2 use identical guide algorithms.
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Old 11-09-2014, 11:39 PM
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Quote:
Originally Posted by codemonkey View Post
...

This is only at 600mm... I've also bought a new scope that I haven't had a chance to use yet, an RC8... I shudder to think what the graph would look like on the RC8!
This is what you could get using an RC8 and OAG so dont panic. I grabbed this tonight. I use CCDSOFT, but the settings are 50% aggressiveness , 0.01 min move and 1.0 max move using an OAG and the SBIG RGH, 5 second guiding exposures with a 5 second delay.

Www.ccdware.com has a good guiding calculator which works pretty much the same as what PHD2 will do.

I know nothing about the neq6, can't help there, but my setup is well within the capacity of your mount so you just need to tweak.
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Old 11-09-2014, 11:49 PM
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We should get together one evening Lee. Do some trouble shooting. Not that I'm all that technically minded, I've had a little experience with it.
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Old 12-09-2014, 06:15 AM
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Hi Lee

Mate don't go pulling the mount apart!!its a very we'll tuned mount.
I never ever had a occasion where it failed to guide well with guide scope.
The PHD graph is showing it to be too aggressive and slight balance.
Balance isn't equal in all areas of the sky.
The noise is normal for all EQ6.
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  #17  
Old 12-09-2014, 07:40 AM
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codemonkey (Lee)
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Quote:
Originally Posted by LewisM View Post
Check RA spur gear tolerances. Replace the factory grease. Remove any detritus that has stuck in/on the grease. Backlash in Dec was always a major issue for me, until I cleaned, polished, re-meshed the tolerances.
Ok, thanks for the tip Lewis :-)


Quote:
Originally Posted by cometcatcher View Post
Your guide star looks horrible. I'm not surprised PHD is having trouble guiding. Are you trying to guide on a waaay off axis star? I haven't used my OAG for years but star quality wasn't it's strong point.
I get all kinds of crazy shapes with the OAG, from slits, to triangles to crescents, depending on how it's adjusted, but the one thing that I never get is a normal looking star. I'm pretty confident that this isn't related to the star shape as I saw the same kind of movement when trying to guide with the Atik 314L on axis.

Quote:
Originally Posted by Shiraz View Post
No, you certainly don't need to take it to bits - only do that as a last resort. There are some hex head bolts that lock the worm carrier to the main body. You undo them very slightly so that the worm carrier can slide on the body and then use the small opposing screws to wind the carrier in or out to adjust the clearance. Then tighten the main bolts back up. takes about a minute when you get the hang of it. It is a normal part of owning an EQ6 - they are even supplied with the key wrenches to do it.

This shows you how and explains what the process does (you should not need to do the end float adjustment on the worm bearings though)
http://www.astro-baby.com/EQ6%20rebu...0alignment.htm

others have commented on the guide star image quality. I have found that the centroid calculation in phd is quite OK with images like yours - it seems to be doing well in DEC in your case and I doubt that there will be any problem in RA. However, it is worth choosing an unsaturated star, rather than one with obvious saturation like the one in your example.
Awesome, thanks mate.

I've tried various exposures to try and reduce the effect of seeing, lending me to blown stars (worse than seen here) and well exposed ones, but the problem persists regardless.

I agree, the fact that DEC is fine suggests to me that the shape has nothing to do with this.

Quote:
Originally Posted by Peter.M View Post
Honestly, I assume you are using an OAG due to the star shapes. I would take an image and see how it comes out, if star shapes are less than ideal then look into it. My graphs are regularly like this (in arc seconds) and I have no issues with my images.
Thanks Peter, that's what I believed.

I took some exposures in the beginning and ended up with square stars, thus the quest to optimise the graph, but you're right... I could have a horrible graph and good results.

Quote:
Originally Posted by Amaranthus View Post
Lee mentioned that he was using an OAG. As others noted, star shape is not critical - the centroid is based on an assumed not characterized star shape.

I'd strongly advise you try, as a first step, to increase the Westerly bias on the mount. This can really help in keeping the gears engaged. It should NOT be perfectly balanced!

PHD and PHD2 use identical guide algorithms.
Thanks mate :-) I've biased the balance in every possible way, perfect, east heavy, west heavy... it no doubt had an effect but nothing resulted in me having a graph that looked like it would give usable results.

Quote:
Originally Posted by jjjnettie View Post
We should get together one evening Lee. Do some trouble shooting. Not that I'm all that technically minded, I've had a little experience with it.
That sounds great Jeanette!

Quote:
Originally Posted by atalas View Post
Hi Lee

Mate don't go pulling the mount apart!!its a very we'll tuned mount.
I never ever had a occasion where it failed to guide well with guide scope.
The PHD graph is showing it to be too aggressive and slight balance.
Balance isn't equal in all areas of the sky.
The noise is normal for all EQ6.
Hey Louie, thanks for posting mate :-)

The last part of the graph has minimum move set to 1px, aggressiveness to 50% and hysteresis to 10, so I think I can safely rule out the aggressiveness of the software settings as being a factor.

The maximum pulse was also reduced to 400 in RA and 120 in DEC (RA was down at 120 at one point a few nights ago but I bumped it back up because PHD seemed to be struggling to get it back after it went out in one direction).

I also tried shifting the balance at various points after slewing to that location but before recording this chart that you see (there were other charts, different but equally bad).

This was somewhat low on the eastern horizon, and I think it did seem worse than when I was pointed close to the meridian, which might suggest that balance is a factor in it though...?
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Old 12-09-2014, 08:37 AM
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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.
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Old 12-09-2014, 09:21 AM
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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
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Old 12-09-2014, 10:32 AM
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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
Or even better use PHD2's built in drift alignment helper tool.
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