Pentax H90 has a
12.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor and features Prime processor. On the other hand, Pentax RS1500 has a
14.0MP 1/2.3-inch (6.17 x 4.55 mm ) sized CCD sensor .
Below you can see the H90 and RS1500 sensor size comparison.
Pentax H90 and Pentax RS1500 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.