The question of interference patters is central to light theory. I would like to share some pictures that show the same patterns in very unusual situations.
The first picture has been taken with the open body of a digital camera, and a laser beam a pen) shining into the body. As you can see, the same patterns appear that are usually associated with constructive and destructive interference see in the double slit experiment, or in the use of two thin plates showing so-called Newton rings.