flickr photos: http://www.flickr.com/photos/24719437@N03/
Quote:I used PHD for helping to drift align but only to capture images of the star I want to drift align against. I use StarTarg on top of PHD to watch the drift. It really is a joy to use.
Quote:I use PhD guiding for drift alignment all the time, and I've never seen what you describe. The first thing you need to do is to physically rotate your camera in the focuser so that movement in RA and dec follow the horizontal and vertical axes of the display. If doesn't matter whether RA or dec end up on the horizontal sxis, just that moving in RA or dec doesn't result in diagonal star movement on the display.Now, after doing an approximate polar alignment, begin the drift alignment procedure. Slew to a star near 0 dec and the meridian. Calibrate PhD and begin guiding. Now, open the graph, and switch the view from RA / dec to dx/dy. Also, select "off" from the dec guiding algorithm dropdown. You will see either dx or dy, whichever is the one corresponding with the dec axis, to begin drifting. Adjust the mount in azimuth until the drift goes away. You will most likely need to stop and restart guiding each time you move the mount.Now slew to a star near 0 dec and the horizon. Calibrate PhD again (click on "brain", change dec guiding algorithm back to "resist switching" or "low pass filter", and check "force calibrate"). After PhD starts guiding, go to the graph and do the same thing you did before, this time making adjustments in alitude until drift stops.You quickly see that, when you pass through ideal polar alignment, the reported direction of the drift will change. It sounds to me like you might have failed to recalibrate PhD when you slewed to a star near the horizon. You can't drift align in PhD with dec guiding active. Also, if you forget to switch from "RA/Dec" to "dx/dy" on the graph after turning off dec guiding, you will just see a flat line for dec corrections.
Quote:By the way - PHD guiding knows where North & South arewithout rotating the camera.
Quote:Thanks shams42.I have sort of tried what you said above except for rotating the camera.I was just wondering why it continues to read out a North error& doesn't flip to South at some point whenadjusting the elevation?
Quote:I am not sure if I had resist switching or filter turned on.I will have to revisit this.
Quote:I was trying to align the Dec without going near the horizonas I couldn't see any stars close to the horizon from my location.I wondered why that matters? - as the mount was still making Northadjustments which is the Dec axis.
Quote:This is my point:PHD sees an error in elevation & adjusts for it -no matter where your telescope is pointed thereforewhy doesn't the error value FLIP at some stage& go from North to South at the bottom ofthe PHD guiding screen - when you change the elevation?Have you ever looked at those numbers at the bottom of the screen?
Modded C9.25, Vixen SP retrofitted with DS motors and Autostar My pics Stars light the world without, to give us purpose They light us within to give us reason We live in a well-lit abyss.
If you weren't pointed in the right spot and had an azimuth pointing error, that could cause the star to drift in declination -- perhaps consistently to the north.
Quote:This does assume that the guide scope axis is parallel to the main OTA doesn't it? Or in practice is that not a big factor since you are also autoguiding?Ajay
Quote:Good news.I finally got the mount to align with PHD guidingby setting the Dec up on a star near the horizon.The Azimuth was another story.It ended up close but not perfect.My mount Dec angle display was 0.5 degrees out.Correct was 37.5 when it should have been 38 degrees.I managed to get some subframes of Centaurus A _ NGC5128.See pic - very quickly processed.
Quote:Wow, that's too bad. Can you post the details of your setup and your settings in PhD?
Quote:I only have homemade tube rings which have too much play in them - in my opinion.
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.
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
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.
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.