My first attempts at shooting star trails

Hi all.
Below are my first 2 attempts at shooting star trails. The first one is a simple 'B' setting exposure of about 40 minutes. I am a bit puzzled with the result of the second effort, which is composed of 41 shots, each of 30 seconds and combined using stacking software. Can anyone explain to me why the trails are they way they are and not smooth lines as I had hoped for?
Thanks.
[IMG]http://i376.photobucket.com/albums/oo209/Naim-Khan/NK013393.jpg[/IMG]
[IMG]http://i376.photobucket.com/albums/oo209/Naim-Khan/Startrails22.jpg[/IMG]

hi
just out of interest was it a clear night
if not it might be clouds moving
did you check all the 41 images
neil

Thanks Neil.
It was a clear night. The first shot was also taken the same night - I did the Bulb setting first followed by the multiple exposures. The individual shots are all OK. It looks like the stars have moved (so to say) between the shots although I tried to shoot continually , one after the other.

It does look like there are 'gaps' between the exposures, but I'm puzzled by the pattern. If they were consistent gaps I'd suggest the camera was doing dark frame subtraction/long exposure noise reduction operation with each frame.

Did you lock the shutter down with a remote release cord or were you manually triggering each frame?

I was using an infra red remote.

I'd say this is probably it then - inconsistent triggering of the shutter between exposures. Any time spent with the mirror down is time you're missing the moving stars, giving you gaps in the trails.

When stacking for trails I use manual 30s exposures with a cable release and continuous shooting mode, meaning no delays between shots. I can then lock the shutter button down and sit back with a brew whilst the camera does the rest. This leaves no visible gaps when stacking.

Thanks digitalCG. It looks like I'll have to try it again and get myself a cable release before hand.

Yep, I'd say that's exactly what the problem is. The sky actaully moves quite quickly, (try using a telescope with a tracking mount!) and those gaps are the bits you missed while the shutter was down.

Nice tries for a first attempt though!.

I've got to say, though, DigitalCG, that's a great shot!