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Equipment Discussions >> Mounts

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shams42
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Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. new [Re: alpal]
      #4504799 - 04/08/11 11:15 AM

Wow, that's too bad. Can you post the details of your setup and your settings in PhD?

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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: shams42]
      #4505588 - 04/08/11 05:59 PM

Quote:

Wow, that's too bad. Can you post the details of your setup and your settings in PhD?



Sure - I just clicked on the "Brain" function.
These are the settings & although I tried 2 second
capture frames half way through, PHD lost track
altogether so I changed to 1 seconds frames.
The settings below were not altered:

RA Aggressiveness 36
RA Hysteresis 10
Dec guide mode Auto
Dec Algorithm Resist swit
Max Dec duration 520
Dec slope weight 5.00
Calibration (ms) 1540
Min. motion (pixels) 0.55
Search region (pixels) 15
Noise Reduction None
Time Lapse (ms) 0
Camera gain (%) 100
LE port Port 358
LE read delay 0
Force calibration tick
Use subframes no tick
Log info no tick
Disable guide output no tick


I'd be interested to know a good way of tuning my setup.
PHD has never given me 100% good frames.
Re-checking I actually got only 9 reasonable frames out of 30
when taking shots of that Centaurus A galaxy.
My previous time on the Southern Pinwheel galaxy
I got about 20 good frames out of 35.
None of the frames are absolutely perfect.

Is there a way of tuning this double axis closed loop
by perhaps putting in a command from the hand controller on say a x1 forced movement &
looking at how PHD handles the disturbance on the graphs?
(and adjusting accordingly)


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shams42
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Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. new [Re: alpal]
      #4505851 - 04/08/11 09:07 PM

Your settings look kind of off. With RA aggressivenes that low, you are hardly making any corrections in RA. Try these settings and see what happens:


RA Aggressiveness 85
RA Hysteresis 15
Dec guide mode Auto
Dec Algorithm Resist switching
Max Dec duration 1500
Dec slope weight 5.00
Calibration (ms) 5000
Min. motion (pixels) .2
Search region (pixels) 15


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: shams42]
      #4506222 - 04/09/11 02:03 AM

Thanks Shams,
I'll try those figures you've given me.
I have played aroud with RA Aggressiveness.
100% was too much & caused worse guiding.
I know I'm close & I hope it just needs a bit of tweaking.
cheers
Alpal


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: alpal]
      #4506424 - 04/09/11 07:19 AM Attachment (39 downloads)

There might be a clue to the problem.
Look at this tiny crop of one of the worst frames.
You can actually see 2 stars instead of one.
Surely that must be caused by the external guiding scope
shifting it's position?


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: alpal]
      #4506432 - 04/09/11 07:30 AM Attachment (33 downloads)

In contrast this was one of the better frames but still not
perfect pinpoint stars.


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shams42
Pooh-Bah
*****

Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. new [Re: alpal]
      #4506589 - 04/09/11 09:48 AM

Do you know if the direction of elongation corresponds with RA or dec?

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jmiele
Patron Saint?
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Reged: 12/04/10

Re: PHD guiding defies logic. new [Re: shams42]
      #4506649 - 04/09/11 10:09 AM

If it's DEC and you were way off in polar aling, could be that guider based on settings can't keep up witth the amount of error being produced. I don't know PHD well so I can't recommend settings changes but I agree with shams, identify DEC vs RA first. Joe

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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: jmiele]
      #4506656 - 04/09/11 10:12 AM

Hi Guys - the Dec was spot on.
No frame rotation after 2.5 hours.


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shams42
Pooh-Bah
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Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. new [Re: alpal]
      #4506697 - 04/09/11 10:36 AM

Can you stack your frames without aligning stars and post result? I want to see if the errors are in a constant direction or if they curve.

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shams42
Pooh-Bah
*****

Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. new [Re: alpal]
      #4506698 - 04/09/11 10:36 AM

Can you stack your frames without aligning stars and post result? I want to see if the errors are in a constant direction or if they curve.

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shams42
Pooh-Bah
*****

Reged: 01/05/09

Loc: Kingsport, TN
Re: PHD guiding defies logic. *DELETED* new [Re: alpal]
      #4506701 - 04/09/11 10:38 AM

Post deleted by shams42

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Peter in Reno
Postmaster
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Reged: 07/15/08

Loc: Reno, NV
Re: PHD guiding defies logic. new [Re: shams42]
      #4506988 - 04/09/11 12:54 PM

Your scope is pretty big and may be too big (or too long) and heavy for your NEQ6 to handle. That might be why you are not getting consecutive good subs. You must have a hard time adjusting the latitude with heavy load while drift aligning. What is the total load including main scope, guide scope, cameras, etc?

Do you have a small refractor to test? If you can image with a small scope and get nice round stars, then extra heavy load may be the culprit.

Peter


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bardo
scholastic sledgehammer
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Reged: 09/13/09

Loc: US
Re: PHD guiding defies logic. new [Re: Peter in Reno]
      #4507386 - 04/09/11 04:14 PM

differential flexure

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Peter in Reno
Postmaster
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Reged: 07/15/08

Loc: Reno, NV
Re: PHD guiding defies logic. new [Re: alpal]
      #4507461 - 04/09/11 04:57 PM

Quote:

I only have homemade tube rings which have too much play in them - in my opinion.




If that's the case, it's differential flexure. You have to get rid of any flexure you find before fine tuning PHD settings.

I notice you have 80mm guide scope. Is it Orion Short Tube 80? If so, they are famous for focuser flop. Check both focusers (image and guide scopes) for any flop. How is your guide scope mounted: 3-point rings or clam shell rings? I would use clam shell rings since they grip the scope much better than 3 point rings.

Also check to make sure the mounting of primary mirror is tight. If it shifts a tiny bit while tracking, then that's another kind of differential flexure similar to infamous mirror flops in SCTs scopes with moving primary mirrors.

Once you get everything tightened, then you can start tweaking PHD guide settings. I would revert back to default PHD settings and go from there.

Bottom line, get rid of the flexure first. Also check to make sure your scope plus equipment are not too heavy for your mount to handle. The carrying capacity of Atlas EQ-G or NEQ6 is about 40lbs for visual observing. The imaging capacity is about half which is probably no more than 20-25lbs.

Peter


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: shams42]
      #4507880 - 04/09/11 08:54 PM

Quote:

Can you stack your frames without aligning stars and post result? I want to see if the errors are in a constant direction or if they curve.




OK - I'll do that - I never thought of that -
it's a good idea.


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: Peter in Reno]
      #4507888 - 04/09/11 08:58 PM

Quote:

Your scope is pretty big and may be too big (or too long) and heavy for your NEQ6 to handle. That might be why you are not getting consecutive good subs. You must have a hard time adjusting the latitude with heavy load while drift aligning. What is the total load including main scope, guide scope, cameras, etc?

Do you have a small refractor to test? If you can image with a small scope and get nice round stars, then extra heavy load may be the culprit.

Peter




The scope is pretty big.
I do have a hard time adjusting the latitude.
I had to replace the lower latitude bolt as it had bent slightly.
I have since lowered the weight from 18Kgs to 12 Kgs
( which is now 26 lbs total load )
I do have a smalller 4.5" Newt which I could do tests with.


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: Peter in Reno]
      #4507904 - 04/09/11 09:06 PM

Quote:

Quote:

I only have homemade tube rings which have too much play in them - in my opinion.




If that's the case, it's differential flexure. You have to get rid of any flexure you find before fine tuning PHD settings.

I notice you have 80mm guide scope. Is it Orion Short Tube 80? If so, they are famous for focuser flop. Check both focusers (image and guide scopes) for any flop. How is your guide scope mounted: 3-point rings or clam shell rings? I would use clam shell rings since they grip the scope much better than 3 point rings.

Also check to make sure the mounting of primary mirror is tight. If it shifts a tiny bit while tracking, then that's another kind of differential flexure similar to infamous mirror flops in SCTs scopes with moving primary mirrors.

Once you get everything tightened, then you can start tweaking PHD guide settings. I would revert back to default PHD settings and go from there.

Bottom line, get rid of the flexure first. Also check to make sure your scope plus equipment are not too heavy for your mount to handle. The carrying capacity of Atlas EQ-G or NEQ6 is about 40lbs for visual observing. The imaging capacity is about half which is probably no more than 20-25lbs.

Peter




I am using the Orion short tube.
The focuser extension tube looks really low quality.
Maybe that is moving slightly?
The Orion focuser is only held on by 4 philips head screws
which 1 week ago were loose - I did however tighten them.
Just checked it now - it feels tight.
The primary mirror has 3 large adjusting screws with strong
springs behind them.
I don't think they would move much between 2 x 5 minute frames but you have got me thinking.
I have the 2 x 3-point rings not clam shell rings.

Thanks for the tips - I have plenty to consider.
I think that sub-frame with the 2 stars per star image
is a dead give-away - something is moving between the
guide scope & the main scope.
cheers
Alpal


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alpal
Post Laureate


Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. new [Re: alpal]
      #4508098 - 04/09/11 11:27 PM Attachment (31 downloads)

Quote:

Quote:

Can you stack your frames without aligning stars and post result? I want to see if the errors are in a constant direction or if they curve.




OK - I'll do that - I never thought of that -
it's a good idea.




OK here is a stack of 9 in a row - with a frame missing -
without alignment checked - in Deep Sky Stacker.
Clearly the mount is not guiding in Right Ascension.
Remember - I was using Dither Master.
This is a tiny crop of the full frame.


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alpal
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Reged: 06/15/09

Loc: Melbourne Australia.
Re: PHD guiding defies logic. [Re: alpal]
      #4508109 - 04/09/11 11:36 PM Attachment (35 downloads)

And here is a full frame as above.
I think Dither Master causes it to drift
in between frames while it takes 30 seconds to
organise the dither -
if RA is not spot on - it will drift between frames.


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