This is a shot I took of Coney Island at night. My DSLR was being fixed at the time, so I shot it with a Canon G7, which is an advanced compact camera. An interesting thing to note on this shot, is that the aperture is fairly wide at f/2.8. But despite that fact, notice how deep a depth of field we get on the shot. The reason for this is due to the smaller sensor on the compact camera.
On a DSLR in order to get the equivalent depth of field, you would need a setting of about f/13 on a full-frame camera and about f/8 on a cropped-sensor camera. This fact illustrates why it is near impossible to do blurred backgrounds with a compact sensor camera.
Note: this is for photodorks only. To compare the DOF of a compact camera or cropped-sensor DSLR to that of a full-frame camera, you can multiply your camera’s aperture setting by its crop factor. For Canon cropped bodies this will be 1.6, for Nikon it will be 1.5, and for Micro-Four Thirds it will be 2.0.
For compact cameras like my G7, it is a little trickier. You’ll need to first figure out the crop factor itself. To compute this , look up the specifications of your camera on DPReview.com and note the 35mm equivalent focal length of the wide end of your zoom. For example, my G7 has an equivalent range of 35-210mm. The wide-end would therefore be 35mm. Compare that to the actual focal length of the lens (7.4-44.4mm). Then divide the equivalent focal length by the actual focal length to get the crop factor (35mm ÷ 7.4mm=4.73)