As the title states I'm not happy with PHD Guiding.
The reason why I say this is because PHD randomly stopped producing round stars during my last imaging session. I don't what has caused this so I am currently trying to get to the bottom of it.
Any ideas? Why is PHD producing eggy stars?
To help illustrate my point here are to images showing the outcome of my last imaging session.
Hmmmm, Matty, that dosn't look good, firstly are you pretty right on with polar alignment, this is fairly important.
It could also be a balance issue, probably worth checking out, it all comes down to illiminating things in steps, if those are both good, then we have to look at other issues.
Binding motors can also cause this are the pretty free, to your knowledge.
If this is good as well, what guiding rate are you using, maybe it is to long in between corrections, I used to use 1.5.
PHD is usually quite forgiving and usually works very well, and another though have you set your mount in photo mode or the appropiate mode for guiding, it won't do very well if in siderial mode.
Just keep posting and asking I'm sure some one will help you out.
"PHD is usually quite forgiving and usually works very well, and another though have you set your mount in photo mode or the appropiate mode for guiding, it won't do very well if in siderial mode."
If I might but in here, what is "photo" mode?
peter
Last edited by PeterO; 29-07-2008 at 09:54 PM.
Reason: quote
Leon
Ahh just different terminology, I set my mount to sidereal mode and then set the guide rate to .5x sidreal.
Matt
I noticed whe I was using PHD with a Qguider if the seeing was less than good I had to increase the exposure time and turn on 2x2 bining to round out the stars again.
As mentioned PHD is very forgiving with a lot of things, including bad polar alignment. You'll get field rotation but tracking will still be spot on. Sounds like your problem is a mechanical problem, not a software problem.
Check the logs or enable the graph. Sounds like you have an oscillating problem. Likely to be balance (got to push the load not track the fall) or sticky gears/grease, could be anything. Wrong tracking rate on the mount [over compensating]. PEC wouldn't be an issue but I always have it off and let PHD do the corrections.
Make sure your calibration run is ok and track at 1s intervals minimum or you may chase the seeing. As Peter mentioned earlier it will also allow you to push the exposure on your guide camera and have more stars to pick from. You'll also get a better SNR. That should do the trick.
I have never had any problems with PHD before so I am hoping it is a one off problem.
I am pretty thorough with balancing and polar alignment so I am positive that is not what is causing it. Whenever I setup I always balance the scope in both RA and DEC axis before proceding. I then spend an hour or so drift aligning getting my polar alignment as close as I can before doing any imaging.
I haven't set PEC so I let PHD do the corrections. I always use a 1 second exposure or more depending on the guidestar and seeing conditions and I have the Autoguiding rate set at 0.5x.
I'm not sure what is causing this.
Could it be the settings on the mount or maybe PHD?
I am pretty thorough with balancing and polar alignment so I am positive that is not what is causing it. Whenever I setup I always balance the scope in both RA and DEC axis before proceding. I then spend an hour or so drift aligning getting my polar alignment as close as I can before doing any imaging.
I have found that perfect balance can cause problems, especially if the worm is not firm against the drive wheel. By firm I don't mean tight -other problems.
I usually have the scope ever so slightly off balance ie 50g to ensure contact of the gears.
Check for slop by gently pushing the scope in either direction and detect movement before the friction of the clutch is felt.
It may be oscillation due to a loose-ish drive worm/gear contact.
Last edited by theodog; 30-07-2008 at 12:58 PM.
Reason: sp
I have found that perfect balance can cause problems, especially if the worm is not firm against the drive wheel. By firm I don't mean tight -other problems.
I usually have the scope ever so slightly off balance ie 50g to ensure contact of the gears.
Check for slop by gently pushing the scope in either direction and detect movement before the friction of the clutch is felt.
It may be oscillation due to a loose-ish drive worm/gear contact.
Thanks Jeff,
That is interesting. I'll give it a go next imaging session.
I'm thinking of reinstalling PHD so all the settings I might have changed are changed back to default.
I've been getting the same problem with eggy stars, but not all the time. Seems to depend upon where exactly the mount is pointing. I use GuideDog with EQMOD and an EQ6. I think PHD is OK and the mount is at fault. Read on...
Last week I pulled my EQ6 apart. It's a newish (white) EQ6 with clear grease instead of the infamous black goo.
But... the bearings on the worm shafts were rubbish. The worm shafts would not rotate smoothly, it felt like the bearings had square balls... they'd probably been over-tightened at the factory. Replacing the worm shaft bearings with good quality Japanese units (only a few dollars) has made the shafts rotate smoothly.
The 'stepped' worm rotation and rough bearings would surely have degraded the tracking accuracy of the mount.
In addition, I've replaced the main shaft bearings and re-greased the whole lot with cold temperature synthetic grease. That is another story!
check that its not over correcting in guide mode .... you can watch on the screen, if it is drop the aggresion settings down. i use .5 sidereal at 20% aggression as id rather catch up than overshoot.
Have you considered differential flexure between guiding train, and imaging train? You don't need much to cause problems.
Is the egg shape only in-line with RA direction, or does it vary depending on orientation of the cameras, and the pointing direction?
Is it worse or better when changing from near a azimuth target to one closer to the horizon?
If yes to any of the above, it is quite likely to be differential flexure somewhere. You'll probably find PHD is working fine.
I had similar issues, and eventually , after looking at the a range of complex causes, found it was simply 'flex' in my guide camera chain. When everything was stiffenned up (and balanced nicely), the problems reduced significantly.
Differential flexure does sound like a likely candidate for the problems that I have been experiencing. The guide rings I use are very solid so the one thing that may be causing flexure might be my guidescopes focuser. It is not the best of scopes so that may be what has been causing the problems.
Matty, you havent mentioned the sub exposure time you used, sheesh, thats fairly critical to analysing your mount performance .
Have your OTA sightly off balance to avoid backlash (RA), it should always "drive forward". Eggy stars then can be reduced in PS.
Differential flexure can be reduced by mounting the guide scope directly to the OTA (if it isnt) and bolting the guide cam to the guide cam rail too. I image at 3050mm FL with external guide to 20mins this way.
Tonight I sat there for four hours trying to image with PHD and for some reason could only shoot nearly always 1 X 4 Min before that wonderful DONG, DONG, DONG,DONG, etc kept on coming. I'm frustrated as we have a HEQ5 Pro and quite often we have this situation. I thought removing the finderscope on the side of the ED 80 would solve the balance problem in the RA and the scope seems well balanced. Slightly heavy to the east to engage gears. When setting up the mount using the hand control I get to the Set Up after dates etc and I change the auto guiding from .5X to 1X. I thought you would want to guide at this speed????? and also set mount to siderial then off I go. PHD and DONG DONG DONG. We have had at most 7 X 5 Minutes without DONG. Any suggestions as I am lost....... Thanks Mark B
Not Happy With PHD Guiding
.
