Panasonic FS25 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Panasonic SZ3 has a
16.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor .
Below you can see the FS25 and SZ3 sensor size comparison.
Panasonic FS25 and Panasonic SZ3 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 Panasonic FS25 has 32% larger pixel area compared to Panasonic SZ3, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.