Panasonic ZS8 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Venus Engine FHD processor. On the other hand, Panasonic ZS5 has a
12.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor and features Venus Engine HD II processor.
Below you can see the ZS8 and ZS5 sensor size comparison.
Panasonic ZS8 and Panasonic ZS5 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 ZS5 has 16% larger pixel area (2.31µm2 vs 1.98µm2) compared to Panasonic ZS8, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.