Sony Sony A7R cameras have always been more about resolution than speed , but with its latest model, the company has flipped that equation. The 67-megapixel A7R VI is not only Sony's highest-resolution mirrorless camera ever but its first A7R model with a fully stacked sensor. That allows for incredible detail, higher speeds and reduced rolling shutter, making it one of the company's most versatile cameras yet. However, it's also quite a bit more expensive than the previous model.  The key change from before is the switch from a 61MP backside-illuminated sensor to a fully stacked 67MP sensor. That not only gives photographers more detail but also mitigates one of the biggest problems with the previous model: rolling shutter distortion. With a much faster readout speed, you'll be able to use the electronic shutter in more situations and video "jello" will be far less of a problem.…