Pinhole cameras were one of the earliest types of cameras. It's the same science that today's cameras also use. Let us find out more about its working with this activity.
We will build a small box from a corrugated sheet. You can take any available box as well.
Let us make a small square opening in the front. On this piece of black paper, we will make a small hole with the help of a push pin.
One, two or more holes can be tried in different patterns as well.
These two push pins will be used to attach paper with a hole. This will make sure that light can enter the box only through this small opening.
Push pins allow us to change the paper easily. This will be difficult if we pasted it to the body.
Let us cut this A4 size white paper. This will act as our screen. We will make it translucent by adding some oil drops. Any oil will work. I have used groundnut oil.
Flashlight from this phone will be our light source.
We can place it in front of the small hole at the same height. Ruler can be placed as well if we have to measure its distance from the hole. This is useful for doing calculations or analysis.
We can move the light source, forward / backward or sideways.
When viewed from the front , we see a small dot on the screen. Size of the dot or image changes as we move the light source away from the hole. For better viewing, make sure there is enough darkness in the room.
Moving the light source sideways also moves the dot away from its center position. Same is true if I move it up and down.
Can you co-relate the movement of dot on the screen and movement of the light. ?
It moves in the opposite direction. If I move the phone to the left, dot or its image moves to the right. If I move it up, the dot moves down.
Let us bring another phone next to this one.
Can you guess the number of dots on the screen ?
Yes, you are right. We will see two dots. We can verify our findings by moving either of the phone and observing the movement of its image.
As both dots are of the same color, it is slightly difficult.
Let us try to use colored light sources instead. We will use these colored LED light sources. I made these using PVC pipe, 9Volt battery, LED and switch.
Now I can switch on individual light source and identify images formed on the screen.
Let us move pencil in between the pinhole camera and light sources. Movement of the pencil gives us clear indication of how rays are travelling from source through the pinhole.
For the blue light source on the right side, its image is formed on the left side on the screen.
For red light on the left side, its image is formed on the right side on the screen.
Same is true if we stack these color light sources vertically.
From these observations we can say that the light ray switches position as it passes through the tiny hole.
We can build a small model with the help of these LEDs to represent this behaviour.
Red, Green, Yellow and blue LEDs are attached to this plastic sheet. We will consider these as our light sources. This small washer is our pinhole. Plastic sheet on the other side represents our screen. Red LED on the screen will be at this location while the blue one will be on the top. Yellow and green LEDs will also switch positions horizontally. Small washer represents our pinhole. These colorful threads represent rays coming from a light source, passing through the pinhole on the way to screen.
We can make the hole bigger and change its shape as well.
Making it much bigger has an interesting effect.
Now lights of different colors are merging into each other and forming new colors.
How these patterns are formed, we will see in the next video.
If you don't have colored lights or this PVC battery, you can use your existing phone and add color transparent paper in front of the flashlight to create your own colored light source.
Try using different colors and check other combinations as well.
U can as well change the shape of the light source and see what it looks like on the screen !!
Thank you.