Hello again,
I just found out that last week's post on Depth of Field had something missing.
There is another factor which influences depth of field: sensor size.
Not easy to change (buy another cam), but it needs to be mentioned.
The depth of field for a given aperture decrease when sensor size increases.
This means that the depth of field of a smaller sensor (e.g. a compact camera) is greater than that of a larger sensor (e.g. a DSLR). The reason for this is that the light rays have a larger area to diverse over. Thus if the object is not on the exact focal point, the rays will diverse over a larger area before reaching the sensor, causing increased blurriness (might not be an actual word, but you get the idea ;)).
Of course bigger sensors have benefits as well (more light reaches the sensor, which could increase the dynamic range), so don't write them off immediately.
More info can be found here:
http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm
http://photo.net/learn/optics/dofdigital/
And even more on DOF:
http://www.cambridgeincolour.com/tutorials/depth-of-field.htm
