Actually, in looking at the photo, I'm not sure what caused the problem. I had an awful time getting it aligned that night, so maybe it's just off polar alignment. Maybe there is a little tracking error. Or perhaps there is some squishiness because of optics. Possible causes of the optics making stars less round, I think, are that the telescope was not as well colliminated as I'd thought, the focal reducer wasn't working as well as it should, or both. More to think about. -- Thanks, Joe

astrodeb@charter.net wrote:

...

Nice job Joe! Is your tracking error due to polar alignment or periodic error? I found out that my tracking problems were due to periodic error so I ordered the new worm gear for the RA drive.

Rather than (or maybe in addition to) new hardware, can't you use Period Error Correction?

Patrick

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Good points, thanks -- Joe

Kurt, I think registration is OK but will check that. Thanks, Joe

--- Joe Bauman <bau@desnews.com> wrote:

Actually, in looking at the photo, I'm not sure what caused the problem. I had an awful time getting it aligned that night, so maybe it's just off polar alignment. <snip>

I understand you took individual LRGB images. How far about in minutes did you take the first and last picture. M27 is at a lower dec, but it could be field rotation. - Canopus56 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com

Hi Joe, Refresh my memory, please. Could you describe your set up? Specifically the scope, camera, focal reducer (if any) and does your setup allow the ability to guide your images? If yes to the latter are your pictures auto-guided, manually guided or unguided? Also, how do you polar align (T-Point, drift method, etc.)? Patrick

Joe Bauman wrote:

I use a refractor mounted on top, which is tied in to a Meade Deep Sky Imager that I use as an autoguider alone. But in this case, I think the telescope wasn't balanced right to accommodate the weight on top, and it wouldn't guide well. I need to work on balancing.

So your images are auto guided with the autoguider attached to a guide scope which is mounted on top of the main scope. And the images are shot through the main scope. Have I got that right? Have you considered using an off axis guider (I have one you could borrow)? That would allow you to guide on the same light that is hitting the imager. That would also allow some slop in the polar alignment as long as the exposure did not go too long. 'Course if the alignment is within a couple of arc minutes of the pole and the drive works well enough I'd think you could go a few minutes without having to guide at all. Which brings me to my next point:

I use the telescope's go-to method. I level and have the assembly generally pointing to the north star. Then I swing the tube around so it is in what Meade calls the "home" position and turn on the system. It makes a GPS reading then points toward Polaris. At that time I'm supposed to center Polaris by adjusting the wedge and alignment, not using the control keys. Then it swings around to some other bright star, almost always Arcturus, and tells me to center on it using the control pad. That's supposed to get the telescope properly aligned.

I'm not familiar with that method (no surprise as there are probably lots of methods I have not heard of). Does Meade say that method is intended for _imaging_? Again, I'm not familiar with how that method works but knowing what it takes to get a scope's polar axis within a few arc minutes of the pole using the drift method or even T-Point, I wonder if the go-to method is actually intended for visual use, not imaging. It occurs to me that one way to check all this would be to put a permanent pier in concrete in your yard and spend a LOT of time working on getting your polar alignment right. Granted, your skies would not be that great but for this experiment all you want to do is get to where you can produce nice, round, focused stars. Once you are to the point where you get virtually no drift in declination over say 5 or so minutes when viewed at prime focus through a 6 to 12 mm illuminated reticle (which I could loan you if you don't have one) you'll know your alignment is right. Then if the drift is still there you could do some simple experiments to see if it's caused by the drive or the fact the imager is not looking at the same light the finder is. Patrick

Joe Bauman wrote:

I don't know about a distinction between aligning for viewing and for photography, with this setup. Another thing to check into.

Joe, there's a simple and straightforward way to find out if the auto alignment is suitable for imagining. You'll need an illuminated reticle, one that will give you at least 100 power (use a barlow if necessary). Like I said before, if you don't have one I'll loan you one. Once you've got the reticle, set up your scope and have it polar align itself. Then insert the reticle, power it up and locate and focus on a test star located near where the celestial equator crosses the meridian. Turn the reticle such that one of the lines is aligned east-west and put the test star on the line. Then, with the RA drive running and any Dec drive disabled just step back and let it run for 2 minutes. Look back in and see if the star is still on the line. If it is, your polar alignment is fine. If it passes that test, find another test star on the celestial equator but low in the east or west. Then do as above and see how it looks after a couple of minutes. As before, if the star is still sitting on the line all is well. In both cases you are looking for movement above or below the line. Ignore any movement along the line as that kind of movement is caused by the drive, not polar alignment. The nice thing about this test is that it can be easily and quickly performed even in your yard. Light pollution has no effect on the test. Carpe Noctem! Patrick

p.s. I'm off to bore some holes in the sky (flying to Wendover with a friend for a late lunch) so I'll not be able to followup on anything else posted here until later this evening. Patrick