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## Pixar in a Box

### Course: Pixar in a Box>Unit 6

Lesson 2: Mathematics of depth of field

# Out of focus objects

In this video we'll explore what happens when an object is out of focus from a geometric perspective.

## Want to join the conversation?

• At , is that the radius of the blur, or the diameter?
• It is actually the radius of the circle of confusion and not the diameter. It is easy to be confused, because I think the sketch is a bit misleading. It depicts only half of the ray bundle that is emitted from point P, namely the bundle between points D and E. One should imagine another point, let's call if F, symmetrical to point D with point E as the center of symmetry. Now, imagine the rest of the rays that originate from point P and pass through the lens with outermost the ray passing through F. These rays obviously also converge on point A by the bending of the lens. Then, if you extrude this outermost ray to meet the image plane, you will have the full diameter of the circle. I understand, it sounds much more complicated in writing than in sketches, but hopefully, it helped.
• He talks about "moving the Image Plane". I forgot - what exactly determines the distance from the pinhole to the image plane? Because in one video I thought he said the Image Plane was positioned at the focal point. What did I miss? Because that is obviously wrong.
A quick explanation is all I need, thanks!

I have been watching these videos in a blur of confusion, I'm seeing circles all around me. :\

In all seriousness, I really enjoyed all these videos! :-)
• What would the out of focus do?
(1 vote)
• I am so lost thaat i do not now what to do
(1 vote)
• At , is that the radius of the blur, or the diameter?
(1 vote)
• I'm confused. I believe I understand what he is saying in the video, but having trouble picturing this in a real camera. I assume the focal point is fixed for a given lens. Does the image plane move? Is that how you can get a lens with a range of say 35mm to 70mm? Which part does the f-stop control, the aperture? And the focus control the image plane?
(1 vote)
• great video! Thanks Mr VanSchieck
(1 vote)
• How is BC the radius of the circle of confusion, and not the diameter?
(1 vote)
• At , is that the radius of the blur, or the diameter?
(1 vote)
• It is the radius of the blur, not the diameter