When guests take their places, they will find little business-card-sized cards, each with a small hole made by a needle. When they look through this little hole, they will be able to focus on objects that are both close to them and far away at the same time.
In addition, this small hole has another trick up its sleeve! If you move your finger slowly in front of the hole so it blocks out the light, the view will disappear as expected. However if you move your finger in the same way behind the card, the hole will appear to be closing upside down.
How does it work?
The small hole acts like a shutter. Looking through the hole is similar to increasing the depth of field in a camera, and can even be used to make emergency glasses with a sufficient number of small holes.
The effect of closing the hole upside-down is due to the flipped nature of the images which reach our retinas. This will be explained with the help of a presentation slide.
