Last week I wrote at length about the benefits of using a cable release when mounting your DSLR on a tripod. What if you do not have a cable release? How can you then eliminate camera shake from physically pressing the shutter button? You can use the self-timer function on your DSLR. By setting the self-timer to activate the shutter, the camera can come to rest again on the tripod after pressing the shutter to activate the self-timer countdown.
I have read that some photographers do not believe that 2-seconds is long enough for a camera to completely stop shaking. 2-seconds is typically the first setting for a self-timer. I have not done my own experiments to see if that is just some serious nitpicking or if shake does still linger. Given that the next setting for a self-timer on a DSLR is usually 10-seconds, that is quite a long time to wait! If your DSLR has an option for 5-seconds, that seems like the best choice.