1. SENSOR SIZEThe Sony FX30 and FX3 share the same E-Mount but differ in sensor size. The former adopts a new 26MP APS-C BSI sensor, whereas the FX3 has a 12.1MP Full-Frame BSI Sensor.
2. VIDEOThe FX3 records 4K up to 60p without sensor crop. In 4K 120p, there is a 1.1x crop. The FX30 crops by 1.04x up to 60p. If you want 4K 120p however, there is a more significant crop of 1.6x.
3. LENSES AND 4KOn the FX3, using APS-C lenses means recording with the 1.5x crop mode. In this mode, it loses the ability to record in 4K. With the FX30, you can always record in 4K.
4. ISO RANGEThe larger sensor within the FX3 offers a cleaner-looking picture with less noise. It has a larger normal range of 80-102,400 ISO compared to 100-32000 on the FX30.