I used a Nikon D-90 with a Tele-objective at 80mm. There are significant variations in the depth of field. As wider the aperture, smaller the amount of the picture that is sharp and vice versa. I found a brief and very simple explanation (http://physicssoup.wordpress.com/2012/05/18/why-does-a-small-aperture-increase-depth-of-field/). It helped me a lot to understand why this happens.
Here are the pictures I took. All of them are focused on the first faucet. First the one with the smaller aperture F2.8
As you may see, the first plant is blurred as well as most of the background. There is about a 1m diameter area around the faucet with might be considered to be sharp enough.
This is the second one with an aperture of F8
In this one, the nearest plant is sharper, but still blurred.
The last one at F22
In this one the nearest plant is sharp. The same happens with the farther ones. The entire picture is sharp enough to understand every object in it.