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Agent M27
super member
Reged: 02/08/09
Posts: 134
Loc: Tampa ,FL
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I was out for a wonderful night of observing this Saturday, it turned out awesome! I got a total of 150 x 90s of M31 and 60 x 45s of M57. I set-up alignment and balance was spot on. I aligned using 6 stars, taking advantage of the incredibly simple and precise tel-rad, and got my focus dialed in quite nicely. On to the problems...I had only one problem and I dont know how major it is/will be as I haven't gotten around to stacking or processing yet. When checking the images as they were taken via Nebulosity I noticed my target was drifting upwards ( west maybe?) Each of the individual subs had nice round stars, only bloating because of poor seeing, but no trails. After about 90 shots M110 wasn't in the FOV any longer so I aborted the sequence, re-aligned, balanced, focused and slewed back to my target. I began my sequence again, and still the image would shift upwards. I finished this sequence and thought to try something on the other side of the meridian, M57. Now the image shift went to the left (south maybe) and it shifted by a smaller amount. As I said there were no trails to speak of aside from a few gusty breezes. My equipment is a Sirius EQ with EQMOD, Orion 80ED, 350D, and Tel-Rad. This is my 3rd shot at imaging and I did not notice this the other two times. Will this be a problem and how can it be solved? Thanks in advance and clear skies everyone. I will post my results when I get to them.
Joe
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Orion 80ED
Sirius EQ, run via EQMOD
Canon XT Rebel unmodded (350D)
Baader Hyperion 8mm-24mm Zoom
9.7mm, 26mm Plossl
Various Filters
Thinking of what to buy next....
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cdndob
professor emeritus
Reged: 07/28/06
Posts: 657
Loc: The Great White North
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I could be wrong here but my initial guess would be your polar alignment is off and the error is showing up over time. Try drift aligning before your next session and if it goes away after that, problem solved.
Steve
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Alex McConahay
super member
Reged: 08/11/08
Posts: 129
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In 90 seconds, trailing may not be evident. YOu might be able to see it if you blow the picture up a couple of hundred per cent. Or you could take it to Images Plus or another piece of software that can analyze star shapes and find they are not quite circular. In other words--although the 90 second pictures look like there is no trailing, there probably is. Add these things up over time (as you do in 90 some exposures) and what you cannot see in 90 seconds you can see in two hours.
Secondly, you say you got a fantastic alignment off six points. That is good. But what was the part about the Tel-rad? If you are centering with a Tel-rad, you are not using enough magnification. Maybe that is just the way you wrote it, rather than what you actually did.
Thirdly, even if you are perfectly aligned with six stars or more, that does not mean you are polar aligned. One can have a wonderful pointing model, and be half a degree off or more of the pole. (At least on my mount--I am not saying anything for sure about yours, with which I have no experience.)
Will it affect you in the long run--Yes. Obviously you cannot use the shots you have from after the subject of the shot has drifted off the chip! But the ones that happened before that, even were progressively more useless. You will notice when you stack that there will be a darker area around the edge, and in your case it will progressively move up.
Alex
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ClownFish
Post Laureate
Reged: 04/26/05
Posts: 6089
Loc: Singapore
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I agree with the above. It sounds like you were GOTO aligned, but not POLAR aligned. Big difference. Also, just to check, make sure your tracking rate was set to Sidereal, not Lunar.
CF
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Learn all about Polar Alignment and Manual Guiding on my website at www.PetesAstrophotography.com! Or visit my Foreign Service Blog!
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Agent M27
super member
Reged: 02/08/09
Posts: 134
Loc: Tampa ,FL
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Thanks for the insight. The bit about the Tel-Rad was I would find it with the tel-rad then use my Hyp Zoom and adjust the mount to keep it centered from 24mm down to 8mm. Is that the correct process? Now about polar alignment. I peak through my polar scope ( dont know if it matters, but my map of the sky inside of said polar scope is reversed, that is cassiopeia is where Ursa Major is in the actual sky and Ursa major is where Cass is in the sky). Now when I look through it, there is a ring with a small circle, somewhat like an orbit about the crosshairs. I have been aligning by placing polaris inside that circle, not the cross-hair. How does one achieve a more accurate polar alignment than just placing polaris in the small circle connected to the ring. I am using the Sirius EQ/ HEQ-5 mount. I did not notice the dark lanes moving upward as you described Alex, but I did notice for the amount of integration time, there should have been way more detail, dont know if that is because it was drifting or not. The core blew way out as well almost to the point it was the only major detail I could see and that was at 800 ISO, should I go with 400 or 200 and long subs for M31. I see most of the images posted here stick with 800 iso and they have a wonderful core. I will get them processed a bit more and upload them and post the link. All the same I am really enjoying myself with this hobby. This is midly frustrating but it only makes me want to get out more often. Take care and clear skies everyone. Thanks again.
Joe
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Orion 80ED
Sirius EQ, run via EQMOD
Canon XT Rebel unmodded (350D)
Baader Hyperion 8mm-24mm Zoom
9.7mm, 26mm Plossl
Various Filters
Thinking of what to buy next....
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drksky
super member
Reged: 09/01/09
Posts: 113
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Drift alignment is the most accurate way to get your mount polar aligned. Google "drift alignment tutorial". There are several excellent explanations of the process.
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Tony C
AT8RC
C6-R
CG-5 ASGT
ST80 w/StarShoot Autoguider
Canon EOS 450D (Stock)
The Drinking Bird
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