Stacking woes from a newbie

[Ook]

Hello everyone. My interest in astronomy experienced a resurgence recently, after finding my old telescope in a cupboard (and subsequent, necessary, cleaning it). As I've become involved with photography in the interim, I decided to read up on astrophotography and give it a whirl.

Whew, there I was thinking macro was technical! I read a book on digital astrophotography, and tried taking a series of images a few weeks ago so I could become familiar with the software. I found the dark-frame process easy enough, but when it came time to align and rotate the processed stack (I shot from a fixed spot on tripod), I ran into trouble. See result:

http://i15.photobucket.com/albums/a385/Ookpik/POTN/final1.jpg

You can see the two areas in the image that are clear (mid-top-left, and bottom center), which was where I specified my anchor points. I'm not sure why the rest of the image is so warped, though. Ignoring the lines running through the image (trial software), can anyone help me understand what's going wrong?

40D, 17mm (too wide, perhaps?) at f/4

[Adrena1in]

May I ask what software you're using to Stack? My only experience is of Registax and Deep Sky Stacker.

Registax comes across as very complicated, and I was unable to get a good stack of Milky Way shots. The shots were taken over the space of an hour, and even when I specified multi-anchor points, it kept failing to align many of the frames, and the final stack was rubbish.

Deep Sky Stacker, however, is very easy to use, and stacked my images automatically. I was very impressed, and it's all I use now, (though I still use Registax for planetary stacking, as it seems to handle that very well.)

[Ook]

I've been using Nebulosity (I'm on a mac), but I will try to get Registax to work and see if that helps. Thanks!

[Adrena1in]

I'd recommend Deep Sky Stacker first if you can get that on the MAC...much much easier. You just click on the files you want to stack, and click to start stacking. None of that picking anchor points and stuff.

[Nightop]

I think you are dealing with a lot of issues here. Being fixed on a tripod is going to be a problem to begin with. You really need to have a tracking mount of some kind.

Next you want your (as you call them) anchor points to be as far apart as you can. Top Left and Bottom Right, although most stacking software can do well with points much closer together.

In Nebulosity make sure you are clicking on the same star, I usually take my histogram sliders that change the screen brightness, and move the slider "W" slider over close to the "B" slider. All this is doing is changing your screen brightness...it is not affecting your data. Then find an easily identifiable star. ( I usually go side to side rather than kitty corner) Patiently wait for each frame to load and then make sure the circle is around the same star, if it is CNTL Click, if not click on the correct star. Once you have choosen the first star in each frame then do the same for the 2nd star on the opposite side of the frame.

When I have had problems like what I see in your stack, it is usually that I got impatient (usually with the first frame after choosing Translate and Rotate). That first frame seems to take a long time to load.

[Nightop]

Looking at your picture a 2nd time I would say that you did click too soon after choosing T&R. Look at the trial version lines....most of them come to a point in the lower left of the screen and fan out from there.

What camera/lens/scope combo where you using? Part of the problem may also be in coma due to the scope or F ratio of the lens.

[Ook]

I think you are dealing with a lot of issues here. Being fixed on a tripod is going to be a problem to begin with. You really need to have a tracking mount of some kind.

When I have had problems like what I see in your stack, it is usually that I got impatient (usually with the first frame after choosing Translate and Rotate). That first frame seems to take a long time to load.

Hi, thanks for your replies. My main concern with the T+R result is that the two anchor areas are quite clear and well-aligned, indicating that I did the procedure correctly. I'll give it another go based on your suggestions, however.

Looking at your picture a 2nd time I would say that you did click too soon after choosing T&R. Look at the trial version lines....most of them come to a point in the lower left of the screen and fan out from there.

What camera/lens/scope combo where you using? Part of the problem may also be in coma due to the scope or F ratio of the lens.

40D, 17-55mm @ 17mm, f/4.

[Nightop]

If you want to resize them to a smaller size (1024x768) or so and zip them up. I can give you an email address to send them to and I can try stacking them.

Greg