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Pixar in a Box
Course: Pixar in a Box > Unit 6
Lesson 1: How virtual cameras workDepth of field
In this video we'll explore why regions in our scenes can go "out of focus." The region of our scene which is in focus call depth of field..
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At3:11what movie is the girl from?(0 votes)
that is Riley from Inside out
the emotions Joy ,Anger , Sadness,Fear,Disgust.and bing bong (bing bong is not an emotion) are inside Riley's head(0 votes)
What is the meaning of focus at infinity? I observed that when focus slider is set to INFINITY, pizza is blurred. How this can be explained mathematically?(3 votes)
Focus at infinity means that objects infinitely far away will be in focus. In other words, light that's parallel will be focused. That's why objects close up, such as the pizza will not be in focus.(2 votes)
Why cant we have focus from far places(2 votes)
At0:56what causes the rays to fan out?
Is it because we are focusing on one part of the whole image?
If the whole scene is in focus, will all the rays be parallel?
What do they mean hitting the lens at an angle?(2 votes)
how do I become an animater(2 votes)
What was it again? I...just don't understand really much.🙀(1 vote)- How can you use depth of field?(1 vote)
- 0:03- In the previous video, we saw0:04how lenses can focus parallel light rays0:07to a point on our image plane,0:08resulting in a sharp image.0:10This means that if our image plane0:12is set at the focal length of our lens,0:14then objects that are very far away appear sharp.0:19For example, imagine a scene with Joy0:21standing a mile away from the camera, like this.0:25If we look at the scene from the side, we get this.0:29Notice the light rays that bounce off Joy0:31and enter the camera are approximately parallel.0:34If we place our image plane0:35at the focal length of the lens,0:37Joy will be in focus.0:39But what happens when we try and make an image0:41of nearby objects in our scene?0:44Imagine we move the camera so that Joy0:45is standing just a few feet away.0:48Now pick any point on Joy and look at0:50the light rays that are heading from that point0:52toward the lens of our camera.0:54Notice that these light rays aren't parallel,0:56they fan out.0:57Because they're hitting the lens at an angle,0:59they are redirected to a point1:00a little farther away behind the image plane.1:04Over here.1:05And where the light rays actually1:06hit the image plane,1:07they're spread out in larger circles1:09instead of tiny points.1:12This results in an image of Joy1:13which is out of focus.1:15To see this effect clearly,1:16check out this out of focus shot of lights.1:18These blurry circles are known as Circles of Confusion.1:21They're a result of light rays1:23which haven't been focused to a point1:24on the image plane.1:26And when an image is in focus,1:28the circles of confusion are so small,1:30they appear as points in our image.1:33We can bring Joy into focus1:34by moving the image plane back a little.1:37There.1:38At this distance, Joy will be in sharp focus.1:42Remember with our pinhole camera1:43just the size of the pinhole1:44determined how blurry or sharp1:46everything in our image was.1:48And with a tiny pinhole,1:49the entire scene was in focus.1:52But now, with a lens in there,1:54only a slice of our scene will be in focus.1:56And anything which moves outside1:58of this in-focus region,2:00either too close or too far away,2:03will appear out of focus.2:06This is known as Depth of Field.2:08Filmmakers control the depth of field2:10with their choice of lens2:11and aperture, or F Stop.2:14Let's do an example with multiple Joys2:16at different distances from our camera.2:19If our aperture is very small,2:21that would be with a large F Stop,2:23then the depth of field will be larger2:25and the transition from sharp to blurry2:27is very gradual.2:29To see this, let's start with a subject2:31that's in sharp focus.2:33As I move it farther away,2:35the blurry region doesn't change very much.2:37This is Deep Depth of Field.2:40So more than one of our Joys will be in focus.2:43Now, let's increase the size of our aperture,2:45that is, a smaller F Stop,2:47and start again with our subject in focus.(1 vote)
- The depth of field (DOF) is the distance between the nearest and the furthest objects that are in acceptably sharp focus in an image captured with a camera.
Factors affecting depth of field
Effect of aperture on blur and DOF. The points in focus (2) project points onto the image plane (5), but points at different distances (1 and 3) project blurred images, or circles of confusion. Decreasing the aperture size (4) reduces the size of the blur spots for points not in the focused plane, so that the blurring is imperceptible, and all points are within the DOF.
For cameras that can only focus on one object distance at a time, depth of field is the distance between the nearest and the farthest objects that are in acceptably sharp focus.[1] "Acceptably sharp focus" is defined using a property called the "circle of confusion".
The depth of field can be determined by focal length, distance to subject, the acceptable circle of confusion size, and aperture.[2] Limitations of depth of field can sometimes be overcome with various techniques and equipment. The approximate depth of field can be given by:
DOF
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{\displaystyle {\text{DOF}}\approx {\frac {2u^{2}Nc}{f^{2}}}}
for a given circle of confusion (c), focal length (f), f-number (N), and distance to subject (u).[3][4]
As distance or the size of the acceptable circle of confusion increases, the depth of field increases; however, increasing the size of the aperture or increasing the focal length reduces the depth of field. Depth of field changes linearly with F-number and circle of confusion, but changes in proportion to the square of the focal length and the distance to the subject. As a result, photos taken at extremely close range have a proportionally much smaller depth of field.
Sensor size affects DOF in counterintuitive ways. Because the circle of confusion is directly tied to the sensor size, decreasing the size of the sensor while holding focal length and aperture constant will decrease the depth of field (by the crop factor). The resulting image however will have a different field of view. If the focal length is altered to maintain the field of view, the change in focal length will counter the decrease of DOF from the smaller sensor and increase the depth of field (also by the crop factor).[5][6][7][8]
Effect of lens aperture
For a given subject framing and camera position, the DOF is controlled by the lens aperture diameter, which is usually specified as the f-number (the ratio of lens focal length to aperture diameter). Reducing the aperture diameter (increasing the f-number) increases the DOF because only the light travelling at shallower angles passes through the aperture. Because the angles are shallow, the light rays are within the acceptable circle of confusion for a greater distance.[9]
For a given size of the subject's image in the focal plane, the same f-number on any focal length lens will give the same depth of field.[10] This is evident from the DOF equation by noting that the ratio u/f is constant for constant image size. For example, if the focal length is doubled, the subject distance is also doubled to keep the subject image size the same. This observation contrasts with the common notion that "focal length is twice as important to defocus as f/stop",[11] which applies to a constant subject distance, as opposed to constant image size.
Motion pictures make only limited use of aperture control; to produce a consistent image quality from shot to shot, cinematographers usually choose a single aperture setting for interiors and another for exteriors, and adjust exposure through the use of camera filters or light levels. Aperture settings are adjusted more frequently in still photography, where variations in depth of field are used to produce a variety of special effects.
Aperture = f/1.4. DOF=0.8 cm
Aperture = f/4.0. DOF=2.2 cm
Aperture = f/22. DOF=12.4 cm
Depth of field for different values of aperture using 50 mm objective lens and full-frame DSLR camera. Focus point is on the first blocks column.[12]
Effect of circle of confusion
Precise focus is only possible at an exact distance from the lens;[a] at that distance, a point object will produce a point image. Otherwise, a point object will produce a blur spot shaped like the aperture, typically and approximately a circle. When this circular spot is sufficiently small, it is visually indistinguishable from a point, and appears to be in focus. The diameter of the largest circle that is indistinguishable from a point is known as the acceptable circle of confusion, or informally, simply as the circle of confusion. Points that produce a blur spot smaller than this acceptable circle of confusion are considered acceptably sharp.
The acceptable circle of confusion depends on how the final image will be used. It is generally accepted to be 0.25 mm for an image viewed from 25 cm away.[13]
For 35 mm motion pictures, the image area on the film is roughly 22 mm by 16 mm. The limit of tolerable error was traditionally set at 0.05 mm (0.0020 in) diameter, while for 16 mm film, where the size is about half as large, the tolerance is stricter, 0.025 mm (0.00098 in).[14] More modern practice for 35 mm productions set the circle of confusion limit at 0.025 mm (0.00098 in).[15](1 vote) 
is it just me or is joy a control freak?
I mean in the movie, she only allows happy memories(1 vote)
3:11Video transcript
- In the previous video, we saw how lenses can focus parallel light rays to a point on our image plane, resulting in a sharp image. This means that if our image plane is set at the focal length of our lens, then objects that are very
far away appear sharp. For example, imagine a scene with Joy standing a mile away from
the camera, like this. If we look at the scene
from the side, we get this. Notice the light rays that bounce off Joy and enter the camera are
approximately parallel. If we place our image plane at the focal length of the lens, Joy will be in focus. But what happens when
we try and make an image of nearby objects in our scene? Imagine we move the camera so that Joy is standing just a few feet away. Now pick any point on Joy and look at the light rays that are
heading from that point toward the lens of our camera. Notice that these light
rays aren't parallel, they fan out. Because they're hitting
the lens at an angle, they are redirected to a point a little farther away
behind the image plane. Over here. And where the light rays actually hit the image plane, they're spread out in larger circles instead of tiny points. This results in an image of Joy which is out of focus. To see this effect clearly, check out this out of
focus shot of lights. These blurry circles are
known as Circles of Confusion. They're a result of light rays which haven't been focused to a point on the image plane. And when an image is in focus, the circles of confusion are so small, they appear as points in our image. We can bring Joy into focus by moving the image plane back a little. There. At this distance, Joy
will be in sharp focus. Remember with our pinhole camera just the size of the pinhole determined how blurry or sharp everything in our image was. And with a tiny pinhole, the entire scene was in focus. But now, with a lens in there, only a slice of our
scene will be in focus. And anything which moves outside of this in-focus region, either too close or too far away, will appear out of focus. This is known as Depth of Field. Filmmakers control the depth of field with their choice of lens and aperture, or F Stop. Let's do an example with multiple Joys at different distances from our camera. If our aperture is very small, that would be with a large F Stop, then the depth of field will be larger and the transition from sharp to blurry is very gradual. To see this, let's start with a subject that's in sharp focus. As I move it farther away, the blurry region
doesn't change very much. This is Deep Depth of Field. So more than one of our
Joys will be in focus. Now, let's increase the
size of our aperture, that is, a smaller F Stop, and start again with our subject in focus. Moving the subject even
just a little further away causes the blurry region to get big fast. This is called Shallow Depth of Field. Now, just a tiny slice of our scene will be in focus. So with a small aperture, or large F Stop, the depth of field is deep. The entire scene is in focus. With a larger aperture, or smaller F Stop, the depth of field is shallow. Only a small slice of
our scene is in focus. In the next exercise, you'll have the opportunity to explore how both aperture and lens length affect depth of field.