Sony S980 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor . On the other hand, Sony W730 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the S980 and W730 sensor size comparison.
Sony S980 and Sony W730 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. On the other hand, since Sony S980 has 32% larger pixel area compared to Sony W730, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.