“One should really use the camera as though tomorrow you’d be stricken blind.” - Dorothea Lange





There are three elements that make up exposure.



ISO determine the image sensor’s sensitivity to light. The higher the ISO (800, 1600, 3200) the more noticeable the grain in one's photography.



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The Aperture controls the lens’ opening, which controls the amount of light traveling through the lens to the camera's sensor. The aperture setting is indicated by the f-number. The lower the f-number (f 1.2, f2.8, f3.2) the more light you are letting into your camera's image sensor. A low f-number means a smaller area of your picture will be in focus.  This is now as a shallow DOF (depth of field). The higher the f-number (f 16, 22, 32) the less light you are letting into the image sensor. A higher f-number means a larger area of your picture will be in focus.

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The Shutter Speed indicates the speed in which the curtain opens then closes. Your shutter speed is measured from fractions of a second all the way to 30 seconds. It depends on what you would like to convey within your picture.









When these three elements are combined, they represent a given exposure value (EV) for a given setting. Any change in any one of the three elements will have a measurable and specific impact on how the remaining two elements react to expose the film frame or image sensor and how the image ultimately looks.


For example, if you increase the f-number, you decrease the size of the lens’ diaphragm thus reducing the amount of light hitting the image sensor, but also increasing the DOF (depth of field) in the final image. Reducing the shutter speed affects how motion is captured, in that this can cause the background or subject to become blurry.


However, reducing shutter speed (keeping the shutter open longer) also increases the amount of light hitting the image sensor, so everything is brighter. Increasing the ISO, allows for shooting in lower light situations, but you increase the amount of digital noise in the photo.


It is impossible to make an independent change in one of the elements and not obtain an opposite effect in how the other elements affect the image, and ultimately change the EV.



Think of it as a scale when you take light from one element you have to replace with another. If I'm shooting a basketball game and want a faster shutter speed I have to add light by either increasing my ISO or lowering my f-number/aperture.



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