The Sony a7R III is a happy medium between the super-fast a9 and the older a7 II, mixing high resolution with a fast burst speed. The camera has the same resolution as the predessor, but offers a significant increase in speed along with sharing a few other characteristics with the pricier a9.
The a7R III uses a 42.4 megapixel sensor, that's the same resolution as the predessesor, but while the resolution is the same, the sensor uses an on-chip microchip for handling those large files faster. Add in an updated processor and the A7R moves from 5 fps to 10 fps in the III. Doubling the speed also requires an even faster autofocus, and Sony says the a7R III offers that with 425 autofocus points on teh hybrid system.
Like the predessesor, the Sony a7R III uses a five-axis sensor shift stabilization system, allowing photographers to shoot handehld at slower shutter speeds. The same 4K, 30 fps video mode is also included.
The weather-sealed body also hides a few other improvements -- the battery life has more than doubled at a 530 shot rating. Sony also doubled up on the SD card slots, a plus since taking big files even faster will fill up that card faster. Much of the rest of the body remains similar to the previous option, including a tilting LCD screen.
The Sony a7R III mixes high resolution files with big speed. The closest competitor with that mix is the Nikon D850, which isn't quite so fast but has a longer battery life as a DSLR. The a7R III has a similar price as well, listing at about $3,200, significantly lower than the speedier, but lower resolution Sony a9.