The light going through two holes at the far end of a film can and then one hole near the eye.
The ray through the top hole strikes the bottom of the retina.
I see three lights
Introduction
A film can and a pin, can be used to create an interesting puzzle in perception.
Material
A black film can with a lid
a push pin (Push pins are slightly larger than sewing pins and make larger easier to use holes.)
A brightly lit white wall or board.
Assembly
In the center of the bottom of the film can poke a single hole with the push pin.
Near the center of the lid poke three holes making a right angle triangle, the holes should be about one hole diameter apart. The pinholes will be very close to each other. Almost touching.
o
o o
put the lid onto the film can.
To Do and Notice
Look through the single pinhole at the three holes and at a bright white wall or board beyond.
What do you see?
Notice that you see the three hole triangle.
Next, look through the three holes at the single hole.
What do you see?
Notice that you see three holes in a triangle!
Now look more closely.
When you look through the single hole.
Is the triangle of holes upside down?
Is it reversed right to left?
Notice that the triangle appears right side up and not reversed.
Look though the three holes at the single hole.
Is the triangle of holes upside down?
Is it reversed right to left?
Notice that the triangle is upside down and reversed right to left.
What's Going On?
When you place the single pinhole near the front of your eye it makes a pinhole image of the three hole triangle on your retina. The image on your retina &emdash; like any pinhole image &emdash; is inverted and reversed right-to-left.
Your eye normally inverts and reverses images and your brain perceives them right-side-up, and unreversed.
So you see the pinhole image right side up and unreversed.
When you look through the triangle of pinholes,
each of the pinholes makes an image of the single pinhole at the far end of the can on your retina.
So you see a triangle of images of the front pinhole.
The triangle of images is right side up and not reversed right to left on your retina.
So, when your brain does its normal inversion and reversal, you perceive a triangle that is upside down and reversed right to left.
Etc.
An image reversed upside down is called an inverted image.
An image reversed right to left is called a perverted image.
In this activity we created an inverted-perverted image.
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Scientific Explorations with Paul Doherty |
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22 May 2000 |