Nikon P510 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features Expeed C2 processor. 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 P510 and SX40 HS sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon P510 and Canon SX40 HS Cameras
Nikon P510 and Canon SX40 HS 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 Canon SX40 HS has 32% larger pixel area (2.34µm 2 vs 1.76µm 2 ) compared to Nikon P510, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.
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
Nikon P510
or the
Canon SX40 HS ,
including hyperfocal distance.