Star trails help

[maddycanon]

Hi there
I've shot a few star trails over the past few months, and a few times I've run into this problem of 'wobbly' star trails. I've tried weighing down the tripod, but even on really still nights with no wind it ends up really scattered. All the photos were triggered by a remote (so I didn't touch the camera between photos).

I have a relatively cheap tripod, but I don't have the funds (broke uni student) to get a proper heavy tripod. Am I doing something wrong? Anything I can do better in terms of reducing and preventing the scattered stars?

example 1:
canon 600D, tamron 18-270mm lens.
19 photos @ ISO 400, f/3.5 and 30 seconds exposure.
I was set up on my veranda, there was no wind at all.
StarStaX_IMG_0988-IMG_1019_lighten.jpgStarStaX_IMG_0988-IMG_1019_lighten1.jpg

Example 2:
canon 450D, 18-55 kit lens + fish eye extension
100 photos @ ISO 1600, f/3.5 and 30 seconds exposure.
set up in a field, slight breeze. I had my car parked behind the tripod to block the breeze a bit (and for me to sit and wait in )

full1.jpgfull11.jpg


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