Sony A580 has a
16.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz processor. On the other hand, Sony A6100 has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Bionz X processor.
Sony A6100's sensor provides 8MP more than Sony A580's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the A580 and A6100 sensor size comparison.
Sensor Size and Resolution Comparison image of Sony A580 and Sony A6100 Cameras
Sony A580 and Sony A6100 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 A580 has 49% larger pixel area compared to Sony A6100, 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 A580
or the
Sony A6100 ,
including hyperfocal distance.