Lightweight and small, but powerful...

As a means of sneaking a spare backup body along on travels, I'd sling a crop-sensor DSLR around my neck with a travel zoom on it. It didn't get counted as a "carry on" so I had a backup body along in case one of my work cameras went toes up (since it could use my good lenses), and one that didn't take up space in with the actual camera gear at that.

With an 18-135mm EF-S travel zoom on it, I also used it to snap pictures at the airport or out the plane window.

Thing is, even on a small Canon Rebel body, like the T1i in the picture above, it's a lens the size of a beer can mounted on a single-lens reflex camera.

The camera body has to be a certain minimum size because it needs room for the mirror box and pentamirror that make an SLR an SLR. Further, despite using a "crop" or "APS-C" sized sensor, which is a fraction of the size of a 35mm negative, the flange diameter of the Rebel's EF/EF-S lens mount was dictated by the size of the 35mm film it was meant to work with.

Enter the mirrorless EOS M6, the silver camera on the right in the top photo. By dispensing with the mirror box and its associated eye-level optical finder, the camera is made much smaller.

And despite using a sensor that is the same physical size and resolution as current Canon Rebel DSLR's, the M6 uses the new EF-M (for 'mirrorless') mount, which has a flange diameter optimized for the APS-C size sensor. That's why, despite having the same Image Stabilization feature as the 18-135mm lens on the Rebel, the even longer 18-150mm EF-M mount travel zoom lens is the size of a little V8 juice can instead of a beer can.

Plus, with an EF-to-EF-M adaptor thrown in my camera bag, it can serve the same backup body function as the Rebel, and be a lot smaller hanging around my neck in the airport.
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