# Physical explanation for camera DOF (depth of field)

• Kirl
In summary, depth of field refers to the range of distances in a photograph that appear sharp. This is affected by the size of the diaphragm (camera opening) and the distance between the lens and sensor. By adjusting the diaphragm, we can control the maximum and minimum object distances, thereby changing the depth of field. This is why different cameras can produce photos with varying levels of background blur.
Kirl
http://en.wikipedia.org/wiki/Depth_of_field" stands for the range that is sharp on a photograph.

The bigger the diafragma (camera opening) the smaller the range that will be sharp on the picture. A bigger diafragma also means a shorter shutter opening (so the picture doesn't become too bright).

I'm interested in the physical explanation of this effect. The explanation on wikipedia is much too technical for me to follow.

I am not a physicist I just enjoy reading about it, so please explain as if to someone who has no idea about the field, thanks.

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Kirl said:
"[URL
I'm interested in the physical explanation of this effect. The explanation on wikipedia is much too technical for me to follow.
.
Use the how things work explanation
http://www.howstuffworks.com/

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See the attached diagrams.

For perfect focus (top diagram), the image has to be located exactly at the sensor plane. Only one object distance can produce this, for a given focal length and lens-sensor distance.

When we move the object to the left (middle diagram), the image also moves to the left, in front of the sensor, and we get a circular spot on the sensor, which is often called the blur circle. In practice, we can tolerate a blur circle up to a certain maximum size, which corresponds to a certain maximum object distance.

When we move the object to the right (bottom diagram), the image also moves to the right, behind the sensor, and again we get a blur circle. The maximum tolerable blur circle size corresponds to a certain minimum object distance.

The distance between these maximum and minimum object distances is the depth of field.

If we make the lens effectively smaller by putting a diaphragm in front of it, but keep the object and image distances the same, we get a smaller blur circle. To get the same maximum blur circle size as before, we need to increase the maximum object distance and decrease the minimum object distance, which increases the depth of field.

#### Attachments

• dof.gif
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In theory, every lens has zero depth of field (focusing light into an image from only one distance exactly) and a pinhole-camera has infinite depth of field (rays from any distance produce an image). In practice, there is always a continuum (ie. you can close the aperture slightly to get a slightly more pinhole-camera-ish result).

Incidentally, this is also why big heavy expensive cameras tend to produce photos with aesthetically blurred backdrops, whereas in a small digicam's photo your eye is distracted by the detail in every item of litter in the background.

## What is depth of field (DOF) in a camera?

Depth of field refers to the range of distance in a photograph or video that appears acceptably sharp and in focus. It is determined by the aperture, focal length, and distance from the camera to the subject.

## How is DOF affected by aperture?

The aperture, or the opening in the lens through which light enters the camera, plays a major role in determining the DOF. A wider aperture (smaller f-stop number) will result in a shallower DOF, while a smaller aperture (larger f-stop number) will result in a deeper DOF.

## What is the relationship between focal length and DOF?

The focal length, or the distance between the lens and the image sensor, also affects the DOF. A longer focal length (zoomed in) will result in a shallower DOF, while a shorter focal length (zoomed out) will result in a deeper DOF.

## How does the distance from the camera to the subject impact DOF?

The closer the subject is to the camera, the shallower the DOF will be. This means that the background will be more blurred and the subject will be more in focus. Conversely, the farther the subject is from the camera, the deeper the DOF will be, resulting in a sharper background and less focused subject.

## Can DOF be adjusted after a photo is taken?

While DOF cannot be changed after a photo is taken, it can be manipulated through post-processing techniques such as blurring or sharpening specific areas of the image. However, the amount of DOF captured in the original image cannot be altered.

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