Canon SX740 HS has a
21.0MP 1/2.3 (6.17 x 4.55 mm ) sized BSI-CMOS sensor and features DIGIC 8 processor. On the other hand, Canon SX420 IS has a
20.0MP 1/2.3 (6.17 x 4.55 mm ) sized CCD sensor and features DIGIC 4+ processor.
Below you can see the SX740 HS and SX420 IS sensor size comparison.
Sensor Size and Resolution Comparison image of Canon SX740 HS and Canon SX420 IS Cameras
Canon SX740 HS and Canon SX420 IS 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.
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
Canon SX740 HS
or the
Canon SX420 IS ,
including hyperfocal distance.