Complex sentence: The Four Thirds system uses a 4:3 image aspect ratio, in common with other compact digital cameras but unlike quasi-APS-C or 24 × 36 mm DSLRs, which usually adhere to the 3:2 aspect ratio of the traditional 35 mm format.
Split into simpler sentences: The Four Thirds system uses a 4:3 image aspect ratio, like compact digital cameras. In contrast DSLRs usually adhere to the 3:2 aspect ratio of the traditional 35 mm format.