The depth of field depends on:
-focal length
-sensor size
-aperture
-focal distance
The depth of field does not, all of a sudden, change from sharp to unsharp. It is more of a gradual transistion. Actually, everything immediately in front of or behind the focusing distance begins to lose focus, although it may be so slight that our eyes or resolution don't perceive it. Since there is no definite point of definite transition between sharp and unsharp, the term "circle of confusion" is used to define how much a point needs to be blurred in order to no longer be perceived as acceptably sharp. This is an exaggerated diagram of circle of confusion. In reality, it would be just a tiny fraction of the camera's sensor area.
An acceptable circle of confusion is loosely defined as one that would go unnoticed when the photo is put onto an 8by10 print, and viewed from 1 foot away.
These are three photos taken from the same point, with different focuses.
How aperture affects DOF:
As the aperture gets smaller, the depth of field is increased. If you want very great depth of field, use a very small aperture. If you want the effect of a blurred background, with a smaller amount of the picture in focus, set a higher aperture. This means to set the f/stops smaller if you want the photo having a greater DOF.
The focal length is how close to the subject your actual lens is. With a longer focal length of the lens, the DOF will be shallower because the lens is closer to the subject. If you use a shorter lens, the background of the subject will be less blurred. If a very long lens is used, the back of the subject will be very blurred, since you are so far zoomed into the subject.
Sensor size:
The actual size of the sensor affects the Depth of Field. The smaller the sensor size, the greater the depth of field is at a given focal length and f/stops. Sensor are classified by their crop factor. Using this, the sensor is compared to a frame of 35 mm film. If a camera has a ratio of 1/4.5 (the one being the comparison to the frame of film) it has a smaller sensor size than that with a ratio of 1/3. The greater the denominator, the less the sensor size.
2 comments:
Good start ...
You list three things that effect DOF.
How do they? Aperture ... when it is a bigger hole (represented by a smaller F-number) ... do you have more or less DOF (and thus more or less in focus?)
Closer to the subject has what effect?
How does the type of camera effect DOF?
There is another aspect as well ... what is it? (Most sites list this as the third rather than "camera type")
Focal length and proximity to the subject are a little different.
Longer focal length (zoomed) = less DOF.
Being closer to the subject = less DOF (but this could be with a wide lens as well ... regardless of the focal length, if you are closer it = less DOF.)
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