Long Exposure Question

[Ryewolf]

So, the last two evenings I've been up on Pendle Hill attempting to do some long exposure light trails, with limited success. Yesterday I thought the movement was caused by me not tighning up the tripod correctly, so today I made sure.... However there still seems to be quite a lot of movement..

Camera Settings: Camera 800D, Lens Canon EF 24-105mm f4, f7.1, iso200, 15secs, -0.7ev, manual focus for both shots, I was also using a remote shutter control.

The 2 images were taken 2 shots apart, as you can see there's a very obvious movement in the first but not the second...

I did come up with a few possible explanations

a/ Car speed caused either ground movement or air turbulence
b/ Tripod leg was touching the car and movement caused by that
c/ Earth spin
d/ Image stablisation was on

Though to be honest I'm a bit mystified as to why it happened on most images but not all....

[Black Pearl]

The IS is on.

On short exposures and unless your tripod is absolutely rock solid I'd leave it on - as soon as the exposures run over a second or so knock it off as it over compensates and creates what you are seeing. I get this almost every time I start doing night shots as I almost always forget to knock it off.

[Rick448]

As above, turn the IS off. 

[Ryewolf]

Thanks BP and Rick, I so rarely do long exposures that I almost enivitably forget about the IS... ahh well, 3rd time lucky....