If you are doing long exposures at night and on or near large bodies of water ensure you get a/the correct tripod - in short, make sure that the tripod has a somewhat good design that provides some vibration dampening.
In short, the very basic starting point is this:
1. Stop down your aperture all the way
2. Ensure you use the "2sec timer" also known as the "Beginners Mirror Up Function"
3. Shoot the scene
While in "AV" mode, your camera's LCD information will blink if the camera's internal thinks you have an improper exposure (ignore it) - also, the max exposure time you will get with the above is 30sec, just starting out this is fine.
If you only want a 15sec exposure, open up your aperture a little or up your ISO - I personally shoot at the lowest ISO possible when shooting night time long exposures, that is however only a preference of mine and you can go with whatever ISO setting you seem fit.
Good luck and share some of the pictures with us
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Last edited by joe.penn; 11-20-2011 at 11:19 AM.