Ahh, guys, this DOF stuff :) If you take different sensor size cameras of the same brand (let's say a Nikon D700 vs. D90), and mount the exactly same lens to it, what happens? Only one thing. While the APS-C sensor size is smaller, some cropping occurs. The effect will be the same as you crop it down in Photoshop. This is why it is often called crop factor. The common misunderstooding (it works like a 1.5x longer lens) comes from this. Yes, an 50mm lens shows less on an APS-C camera, exactly the same field of view, what a 75mm lens does in full frame. But the lens is the same, no DOF, no f-stops, nothing else changes. (Maybe you get somewhat better results with some lenses because the sensor crops your edge effects like vignetting, CA or blurriness :D)