blurring things

[jihad]

So I am a beginner with 2 cameras:

Old: Canon S5 IS (P&S)

NEW: REBEL XTi (DSLR)

I thought I understood how to blur the background of a pic but I guess I do not. So here is a stupid question:

My P&S can reach a F/2.8, pretty low. However I never manage to blur the background. Yet my REBEL can Blur the Background even with a F/4.0.

Why is that ? I felt that when I focus on an object in P&S the contrast between in and out of focus is not that big... unless I use Macro, but is still not that big.

Thanks

 

[Samanax]

Depth Of Field (DOF) of P&S cameras are generally deeper at a given f/stop than a similar f/stop with your XTi. The difference has partly to do with the size difference between the image sensor in a P&S and the XTi...the XTi image sensor is over 10 times larger. You can check that out here. The image sensor in most P&S cameras is 1/2.5". Compare that to the Canon APS-C sensor size on that Wikipedia page.

The lens size has something to do with the difference as well as the distance between the back of the lens and the sensor. DSLR lenses are obviously much bigger than the lenses in P&S cameras.

Depth Of Field Tutorial

Examples For Understanding DOF