Sony H55 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Bionz processor. On the other hand, Sony H90 has a
16.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features BIONZ processor.
Below you can see the H55 and H90 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony H55 and Sony H90 Cameras
Sony H55 and Sony H90 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 Sony H55 has 14% larger pixel area compared to Sony H90, it has potential to collect more light on pixel level hence 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
Sony H55
or the
Sony H90 ,
including hyperfocal distance.