Nikon S4000 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Expeed C2 processor. On the other hand, Canon SX30 IS has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Digic 4 processor.
Below you can see the S4000 and SX30 IS sensor size comparison.
Nikon S4000 and Canon SX30 IS have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.