Both Olympus SH-2 and Olympus SZ-31MR iHS have 16.0 MP resolution sensors but Olympus SH-2's sensor is 1/2.3' (6.17 x 4.55 mm ) and Olympus SZ-31MR iHS's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Olympus SZ-31MR iHS's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus SH-2.
Below you can see the SH-2 and SZ-31MR iHS sensor size comparison.
Olympus SH-2 and Olympus SZ-31MR iHS 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.