Light Travels in Straight LInes How a Camera

Light Travels in Straight LInes How a Camera Obscura (or “Pinhole Camera”) works

Four Basic Concepts The four basic concepts that are important to consider in understanding pinhole phenomena. 1. 2. 3. 4. Your eye is a light detector Light travels from a source in all directions at once Light must reflect off objects in order for them to be seen Light travels in straight lines

1. Your Eye is a Light Detector Your eye is a detector of light. All it can sense is the light that enters your eye and the position that it lands on the retina. The key inference here is that if you see something, then light from that object must be entering your eye.

2. Light travels from a source in all directions Light travels out from a source. It travels out in all directions. We can see a candle flame from many different positions in a room because light travels from that flame out in all those different direction.

3. Light must reflect off objects in order for them to be seen Since all your eye can do is detect light, anything you see has light traveling from it to your eye. You can see objects that are not self -luminous because light from the sun or other sources reflects off these objects and enters your eye.

4. Light travels in straight lines The light ray model of how light travels is useful because it is consistent with many phenomena that we observe.

Imagine a typical outdoor scene with the sun shining brightly on a tree. ● The light from the sun travels in parallel rays, shown here in black. ● When they hit the tree, the light is scattered in all directions, shown in grey. ● This is known as “diffuse” light. Because of diffuse light you can see the pretty tree, as some of this scattered light hits your eyes.

Now lets imagine we pitch a tent with perfect light blocking material and a tiny hole in one wall. ● To keep it simple, a single ray hitting the tree will diffuse in all directions, but only a very tiny sliver of that light will go through the small hole. ● If you were sitting in this tent in the middle of the floor and you closed one eye and looked through the hole from there, you would only see a very tiny part of the tree at once.

Continued. . . ● If you move to the right a bit, you will see the left of the tree. ● If you move up, you will see further down the tree. ● Your view of the tree is opposite to the direction of your movement.

Of course, there is more than one ray of light hitting the tree! ● These rays reflect diffusely in all directions. This is why you can see more of the tree by moving around inside the tent. ● If we were to set up a screen in the tent opposite the hole, which is made of nice bright white material, we would actually be able to see an image of the tree, projected onto it!

For the reason that we saw parts of the tree in the opposite direction when we moved, the projected image of the tree appears upside down.

Photography 101: Light and the Pinhole Camera Find out more at: http: //digital-photography-school. com/photography-101 -light-and-the-pinhole-camera