Samsung ST80 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor . On the other hand, Samsung ST6500 has a
16.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CCD sensor .
Below you can see the ST80 and ST6500 sensor size comparison.
Samsung ST80 and Samsung ST6500 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.