Nikon 1 J5 has a 21.0MP 1 (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features Expeed 5A processor. On the other hand, Sony A58 has a 20.0MP APS-C (23.2 x 15.4 m ) sized CMOS sensor .
Another difference between these two cameras is that Nikon 1 J5's sensor lacks anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the J5 and A58 sensor size comparison.
As seen above, Sony A58 has a 3.0x Larger sensor area than Nikon 1 J5. 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.