Panasonic ZS20 has a
14.0MP 1/2.3-inch (6.08 x 4.56 mm ) sized CMOS sensor . On the other hand, Canon SX40 HS has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor .
Below you can see the ZS20 and SX40 HS sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic ZS20 and Canon SX40 HS Cameras
Panasonic ZS20 and Canon SX40 HS have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Panasonic ZS20
or the
Canon SX40 HS ,
including hyperfocal distance.