When you buy a camera that can change lenses, you’re actually limiting your choices when it comes to choosing lenses. For the most part, Canon cameras work with Canon lenses, Nikon lenses with Nikon cameras, Sony lenses work with Sony….you get the idea.
If you’re willing to put an adapter in between a lens and camera, however, you can change things up. It’s not a new concept—in the old days, it was easy enough to put medium format lenses on 35mm SLRs—but the move toward mirrorless cameras has made things even easier.
The reason is one of physics and optical design. Lenses are made so they can focus on far objects, as long as they are the proper distance away from your camera’s image sensor. Mirrorless cameras have a very short space between the lens mount and sensor, making it a relatively simple matter to engineer adapters to support lenses from other systems—the most basic adapters are light-proof tubes with the proper mounts on both sides.