Understanding Aperture and Depth of Field

The following are a few notes from the lecture given on September 6th, 2012:

image found here.

“The camera lens is an array of optics, called lens elements, in a barrel-shaped package, positioned on the front of the camera body.” (pg49, Digital Photography: A Basic Manual. Henry Horenstein)

Aperture:
Focuses the subject
Controls the amount of light that gets through to the sensor
Determines what will be included in the picture
Establishes the depth of field
Opening in the lens created by a series of overlapping blades
Adjustable
Controls the amount of light reaching the sensor
Controls depth of field
Also known as f-stop

F-stop:
F-stop refers to the measurement of the size of the aperture
It represents the relationship between the size of the lens opening and its focal length.
It is derived by dividing the measured diameter of the lens opening by the focal-length.
F-stop numbers seem counter-intuitive because the higher the number, the smaller the opening. For example: f/16 lets in much less light than f/4

Depth of field:
“Range of acceptable sharpness in an image—from the closest to the farthest part of the scene.” (pg69, Digital Photography: A Basic Manual. Henry Horenstein)
Deep Depth of Field: Everything is in focus from front to back of image
Shallow Depth of Field:Sharply focused subject but blurry foreground or background
Depth of field can provide a very selective focus and is determined by the aperture
f/1.4 = Shallow Depth of Field
f/16 = Deep Depth of Field
Depth of field is also determined by Focusing distance
For example: 20 ft from subject vs. 5 ft from subject will affect depth of field
Depth of field is also determined by the Focal Length
Short focal length = ability to have deeper depth of field than a longer lens (ex: 24mm vs 200mm)

A few examples of Shallow and Deep Depth of Field:

images by Carolee Beckham