Canon introduced the 100D as "The World's Smallest and Lightest Digital SLR Camera"*. The difference is difficult to appreciate until you put it into perspective: the 100D is less than half the weight and almost half the volume of Canon's popular EOS 5D Mark III model. This scales down the housing considerably and shaves a minimum of 5 pounds (2.3 kilograms) off the equivalent underwater system.
The smaller size has huge advantages in both air travel by reduction of packing weight and underwater travel by reduction of drag and arm fatigue.
Most compact mirrorless cameras have the ergonomics of a point-and-shoot: boxy with tiny buttons. The 100D has the same ergonomics of a larger Canon DSLR camera but shrunk down for portability. The curvy body and thoughtful button placement are an easy transition for the amateur or professional DSLR shooter.
No camera series has better lens support than the Canon EF-S range. Attach any of your favorite Canon lenses including the most popular choices for shooting underwater like the Tokina 10-17mm Fisheye and Canon 100mm Macro USM IS. The EOS 100D has a native Canon EF-S mount, so you don't need an extra adapter which can slow down autofocus and reduced image sharpness.
Whether you're considering a housing for an early model Canon DSLR or a newer mirrorless camera, you can't afford not to look at the 100D. Use the money you save to plan your dream photo trip.
* Among digital SLR cameras which use APS-C size equivalent sensors. As of March 1, 2014, based on Canon's research and claims. Ikelite does not confirm or guarantee this claim.