Companies that make DSLR cameras are in serious trouble right now. Some speculate that Nikon, arguably the best DSLR company in the business, might go bankrupt.

Single-lens reflex cameras use a combination of a prism and mirror. The photographer looks through the lens, adjusts the focus then sets the shutter speed and aperature then snaps the photo.

To take the photo, the SLR flips the mirror which redirects the light from the view finder to the photo element.

This set up does not work with video! That little mirror would have to flap back and forth between each frame and there is not time for the photographer to readjust settngs between frames.

The new "mirrorless" cameras from Sony (and a few others) have photo elements that are pretty much on all the time. The photo elements will sample the light from an image over a period of time. The camera's software will then stitch together a crisp image based on the sampling.

Since the cameras sample the image over a period of time, the cameras do not need the expensive lenses needed by SLR cameras.

The software in digital cameras offer image stabilization. Image stabilization is not that terribly difficult. If the camera noticed that all of the pixels shifted between samplings, that the camera most likely moved.

The current generation of cameras compete on which camera has the best software. Some smart phones have extremely advanced software.

I would not be surprised to see mirrorless cameras completely replace SLR and DSLR cameras in the near future.