The mirrorless cameras are now the most popular choice for high quality underwater photography at low cost and small size. Many people are downsizing from the large, heavy DSLR camera systems in favor of these compact, less expensive cameras. When housed in a Nauticam housing, you can add a full size SLR style viewfinder, and interchangeable ports allow use of a wide range of lenses.
When Olympus offered the first Mirrorless cameras, there was little competition. Now there are dozens available by Sony, Panasonic, Nikon, Fuji and more. How do you choose?
The FIRST consideration in choosing a system for underwater is to find the one with the best housing.
Olympus continues to make their own, wonderful, ergonomic, low-cost housings with clearly marked controls, and light-weight neutral buoyancy. These features are important to divers and are why these systems are so popular.
Another excellent housing option is made by Nauticam. While they are more expensive and complex, and much heavier above and underwater, they offer several important advantages that are worthwhile to the serious photographer. See my review below.