Olympus 1s has a 12.0MP 1/1.7" (7.44 x 5.58 mm ) sized BSI-CMOS sensor . On the other hand, Fujifilm S1 has a 16.0MP 1/2.3" (6.17 x 4.55 mm ) sized CMOS sensor .
Below you can see the 1s and S1 sensor size comparison.
As seen above, Olympus 1s has a 1.5x Larger sensor area than Fujifilm S1. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.