What is Depth of Field?
There are a lot of very technical terms used in cinematography, often combining both the specifics of the video technology, the film language itself, and terminology used in art as a whole. One that you will see commonly in cinematography, both in film and in digital video, is the term depth of field. Depth of field has been ported over from still photography and digital photography as well, and is important for using focus when framing a video image. Depth of field in cinematography tends to refer to the space of image clarity when an image is focused on an object or subject, which means the area where something could be put in front of a camera lens and it will be fully in focus. Here is a more detailed look at what depth of field is when it is being used in digital video cinematography.
Understanding Depth of Field
Cinematography depth of field is where the image is going to come into what has often been called "acceptable sharpness." This means that the depth of field is the area in an image where it is in focus to the level that it can be used. This area is dictated by the type of lens and video equipment that you are using, and will essentially be the area in front and in back of the subject that remains in this "acceptable sharpness." It is up to you to end up dictating exactly how much depth of field you want in your cinematography, meaning how large you want the area of focus to be.
Choices and Examples of Depth of Field
The choices that you have to make when determining depth of field in cinematography is how you want the image to end up looking. The negotiation with the depth of field is also the negotiation for how you want the image to look. If the focus object or subject is going to be larger in your frame then the depth of field is likely to be shorter, and if it is smaller the depth of field will become larger. At the same time, a lower f-stop rating is going to give you a larger depth of field as well. An example of this is going to be how you may portray different types of angles in scene coverage. You will start off with an example of a master shot, which may use a wide angle lens that has a fairly short depth of field. If you choose to use a regular long lens then it will increase the depth of field. If you shoot in a darker scene and open up the iris more and this will decrease the depth of field, and in brighter locations you can close it more and eventually increase that depth of field.
You are also going to want to alter the depth of field in cinematography for different types of films or images you want to produce. An example of this is with very intense dramas where there needs to be a more detailed focus on the characters and their expressions. Here you want to shorten up the depth of field so that the background takes up less attention of the audience.