Growing up, one of my favorite toys was the View-Master. So I was pretty excited when my wife’s cousin found a stereoscope from the mid-1800’s in his grandparent’s closet a few months ago.
Each card has two nearly identical photos taken from different angles. You place the card in a holder on the end of the viewfinder, and slide the card forward or backwards until the two images become one. Because each eye is viewing the image from a slightly different perspective, a foreground and background emerge.