“The single most important thing in photography is Exposure!
Before you have subject matter, focus, composition or emotional response; the image must be visible.
If you cannot see it, it is irrelevant.”
-Seantel Sanders

The definition of exposure is simply how much light is allowed to strike your film or image sensor, controlling how light or dark your image is.

Correctly Exposed image looks just right: Not enough light and the image is Underexposed Too much light, and the image is Overexposed

The camera has 3 controls built in to regulate exposure: Shutter Speed, Aperture, and ISO (pronounced eye-so)*

Shutter Speed: time #

Shutter controls how long light is allowed to enter the camera. Shutter speed settings are generally expressed as fractions of a second. The longer the shutter is open, the longer light is allowed in; the brighter your image will be.

The Major Shutter settings are:
30s, 15s, 8s, 2s, 1s, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, 1/4000

More Light (Brighter) ←—————————————–→Less Light (Darker)

Aperture: quantity #

The aperture is the opening in the lens that allows light in. The bigger the opening, the more light is allowed in; the brighter your image will be.

The Major Aperture settings:
f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32

More Light (Brighter) ←———————————————— →Less Light (Darker)

The math behind the apertures is a bit more complicated than the shutter speeds. The number for the aperture that you will set is called an f-stop. It is a fraction that relates to the focal length and the actual size of the lens opening. For the rest of this course, the term “aperture” and f-stop will be used interchangeably. The number represents a fraction and is displayed like this: F/2 or F8. It translates into a fraction by replacing the F with a 1 and now we see these f/stops actually refer to 1/2 and 1/8.

Viewing the Aperture Diagram below, we see that when the F-stop number gets larger, the hole gets smaller and lets in less light. F8 is a larger number than F2 yet the aperture is smaller and lets in less light. When you convert the f-stops to fractions, it makes more sense, 1/8 is smaller than 1/2, hence F8 lets in less light.

Apertures range in f-stops from F1 to F128 in one-stop increments. Your camera will most likely have a range between F4 and F32. A one-stop increment either doubles or halves the amount of light hitting the film. The whole f-stop numbers are listed below. You will be responsible for committing these whole f-stops to memory.


ISO: sensitivity #

The ISO* describes how sensitive your film or sensor** is to light. The more sensitive to light your sensor, the less light you need to get a good exposure.

The Major ISO settings are:
100, 200, 400, 800, 1600, 3200, 6400, etc.

Although each of these factors impacts the brightness of your image, they also have their own unique, secondary effects on the look of your image:
Shutter: The rendering of Motion
Aperture: Depth of Field
ISO: Grain or Noise

As the semester progresses, we will explore the impact each of these has on our images. For now, we will examine the impact on exposure (brightness) only.


*ISO, although normally presented in all caps, is an actual word that derives from the Greek “isos” which means ‘equal’. Contrary to popular belief, it is NOT an acronym for the International Organization for Standardization. (Links to an external site.)

**(You will often see the word “film” used when explaining different concepts in exposure. Film and digital terminology is interchangeable when discussing exposure. 100 ISO film is the exact same sensitivity as a digital camera set at 100 ISO. Film is still used by many photographers, and the word sounds much better than “digital imaging sensor.”)