Oil Bottle

slurppi I agree. I'm still not quite sure how shutter priority works

Satoshi T Very simply, we assume that ISO is fixed.
In order to get optimum brightness, there are several combinations of Aperture and Shutterspeed.
for example: f2.8and1/30sec, f4and1/16sec, f5.6and1/8sec, f8and1/4sec, f11and1/2sec - These are all, the Same brightness.
Aperture is factor of the width of the objects that are IN forcus.
f11 focuses on the quite a range. f2.8 focuses on main object only.
if object or you are moving, long shutterspeed can cause blurring.
Depending on the picture you want to create, you may select one from these combinations.
sorry, a little longer. :)