Panasonic GF5 has a
12.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine FHD processor. On the other hand, Panasonic GF8 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine processor.
Below you can see the GF5 and GF8 sensor size comparison.
Panasonic GF5 and Panasonic GF8 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 GF5 has 31% larger pixel area compared to Panasonic GF8, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.