[Rainer]

Well depth of field is controlled by several parameters ...

distance to subject, focal length and aperture (plus sensorsize).



Since with modern SLR cameras you see the viewfinder image

through the wide open aperture, you do not see the image under the same

circumstances as the camera will take the image (given that you do not

shoot wide open).



Make a small test:



- Use the longest focal length available on your standardzoom.

- Focus on something near ... very near ... as near as possible.

- select f/11 or f/16 as aperture. (edited to f/11)



Now look through the viewfinder and press and release the

little DOF-preview button several times ... and look on those

areas of the image that are NOT in focus ... that are before or

behind the thing you focussed on. You should see that (besides

getting darker) these parts are also getting sharper when the

aperture is stopped down.