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## Pixar in a Box

### Unit 6: Lesson 2

Mathematics of depth of field

# Thin lens approximation

In this video we'll explore what happens to light rays when they pass through a lens.

## Want to join the conversation?

• Thin lens approximation states that if a ray of light goes through the direct center of the lense, the light is not bent. An unbent ray of light going through the center is called a medial ray. Any other ray of light is called a parallel ray. When parallel rays pass through the focal point of the lens (f) the focal point defines what point a parallel ray crosses the x-axis. Where the rays intersect defines i. i is where the image appears in focus. All rays coming from the same point will intersect in one place at some point. So all points that are parallel to the lens at a distance (o) will intersect in one place. Where they intersect is when the camera is in focus. So, you can use the thin lens approximation to find where the medial ray and parallel ray intersect. By finding the intersection, you can figure out at what point your camera will focus. Hope this helps!
• What is a x axis and what does f stand for?