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Focus, Depth of Field part 2 by Jorg Fedler



Depth Of Field


What is Depth of Field (DOF)?


Here is the scientific version:
Depth of Field (DOF) refers to the range of distances from the camera at which acceptable sharp footage is obtained. So easy!

And here is my version:
At one point only your subject is completely, 100% in focus (sharp). Everything else around this point is slightly
out of focus (soft(er)). Not noticeable though, just to mention this fact for accuracy sake.

In the real world your camera will give you generally acceptable image quality which is sharp (focused) inside a certain area. It is this focused area we call Depth of Field (DOF). Everything else we call soft focus or being slightly or completely out of focus (blurred).

Jorg Fedler
Can you control the Depth of Field (DOF)?
Yes you can. If you have one of the better consumer cameras it will allow you a manual override, meaning deactivating the automatic settings. You will be able to adjust your settings which allow you to control the DOF accordingly to the light conditions and the footage you want to capture.

The DOF is not constant and it can be changed using, for example, the iris setting. The smaller the aperture (iris opening), the greater is the DOF. However, a smaller aperture needs good (bright) light.

Just for clarity: if you have bright sunlight the iris aperture is pretty small which gives you a better depth of field. On the flip side, in low light conditions you will be forced to open the iris more, even to its full extend, to obtain an acceptable image quality and therefore the DOF will be reduced.
Note: small aperture = good DOF, large aperture = shallow DOF.
Again: Bright sunlight demands a smaller aperture and gives you a great DOF. Low light will force you to open up the aperture (iris opening) and the DOF will be significantly reduced, meaning the area in front of and behind the subject are noticeably more out of focus (not sharp).
Simply put:, depth-of-field is how much of an image is in sharp focus from front to back.

But let's get back to our manual camera settings and controls. So what can you do with your manual override to influence the DOF (Depth of Field)?

1. Check if you need any ND Filters - Sunglasses for your Lens
In bright light you can use a Neutral Density (ND) Filter without compromising the DOF too much. Neutral Density Filters come in the following sizes: ND4, ND8, ND16, ND32, ND64. The larger the number, the more light get blocked out. Basically a ND filter will reduce light intensity and will slightly reduce the DOF. Filters are designed to reduce the amount of light. As a general rule you have to think of filters as competitors against the DOF. Trial and error will decide how you finally compose your shot. This means doing the same shot again and again with different settings, in different light conditions, until you are happy with the final product. Many videographers throw in the towl and settle for mediocre footage. Do I hear: NOT ME!!!?
Because cameras work differently I cannot give you any advice for the correct settings for aperture, camera positioning or filter choice. You have to work that out yourself and try until you find the correct setup.

Camera Lens Depth Of Field 2. Adjust the Focal Length of your Lens
Basically, zooming in will reduce your DOF and zooming out (using the default focal length of your camera) will increase your Depth of Field. Since you are aiming for the best DOF, you better leave the zoom in neutral (fully zoomed out). There will be, of course situations where you have to make a telephoto shot, meaning you have to zoom in. Be aware in this case you will have a shallower DOF. The shot can be interesting nonetheless if you can focus on your subject, so the subject will be sharp in focus and the surroundings are slightly or even strongly out of focus (blurred), also called bokeh.
Here is a trick: If you aim for a beautiful bokeh (shallow DOF) footage, zoom fully in, get your subject in focus and shoot.

3. Camera Position
Position your camera as far away from the subject without sacrificing clear visibility of the subject. The farther away the camera is from the subject, the greater is the DOF and vice versa.

These are the important points where you can creatively manipulate the Depth of Field (DOF) with a manual override, camera position and by discarding the use of filters.

Shallow Depth of Field Depth Of Field Now why do you want to play with the DOF and manual override in the first place? Why not just leave the camera in automatic mode? The answer is simple, Creativity.

There will be times where you want a shallow DOF or situations where you want a perfect DOF.

Shallow DOF, for example, will create atmosphere. Shots with out-of-focus trees or flowers in the fore- and background are classic examples. Subjects can be separated from their background: try a telephoto shot picking out one face from the crowd or, for impact, take a deep-focus shot in the wide angle position that shows for sharp details going from front to back.

Depth of Field can be an interesting playground for videographers. It gives you opportunities to make your footage look more interesting, just a notch or two above the average. Isn't that what we all aim for?



Bringing it all together Factors which influence the Depth of Field (DOF)

  • Lightning conditions (more light is better for a good DOF)
  • Camera filters (filters reduce the light intake, DOF is more shallow)
  • Shutter speed (does not influence the DOF)
  • Digital Gain (not mentioned in this article). Just be aware that digital gain can easily ruin your takes. It will put more grain into your footage.
  • Zoom (changing the focal length of your lens. Zoom-in reduces the DOF)
If you aiming for the greatest possible DOF
  • Add more light (refers mostly to inside shooting)
  • Change or remove filters to allow more light reaching your camera's sensor
  • zoom out fully
To reduce the Depth of Field (DOF)
  • zoom in fully
  • Increase the aperture, open up.
  • Add filters
  • Use the Portrait Effect many consumer cameras offer. Activating this feature reduces the DOF by adding a little shutter speed which forces the iris to open wider.

Good to know: Shutter speed has no direct affect on depth of field.

If you are constrained to a particular exposure settings there are at least three other things you can do to change your Depth of field.

Focal length
If you need a shallow DOF choose a longer focal length or if you need more depth of field choose a wider focal length. With an aperture of f8, a 30mm lens a subject 10 meters away will give you an infinite DOF. Change to a 200m lens you will get a DOF of around 1.2m

Distance
If you need a shallow DOF get closer to your subject. If you need deeper DOF get further away from your subject.

Sensor Size
Bigger sensor do not necessarily influence the DOF.

That's it folks. Becoming a creative videographer needs a bit of work on your behalf. On the other hand, you will be rewarded with great looking footage.

Tips and Tricks - Depth of Field

In this tutorial Tom Antos explains the depth of field and how you can control it. He also breaks the old myth that a larger image sensor in your camera equals a smaller depth of field.

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