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  6. Aperture

Digital SLR Camera Basics

Aperture

Aperture controls the brightness of the image that passes through the lens and falls on the image sensor. It is expressed as an f-number (written as “f/” followed by a number), such as f/1.4, f/2, f/2.8, /f4, f/5.6, f/8, f/11, f/16, f/22, or f/32.

Changing the f-number changes the size of the aperture, changing the amount of light that passes through the lens. The higher the f-number, the smaller the aperture and the less light that passes through the lens; the lower the f-number, the larger the aperture and the more light that passes through the lens. For example, changing the aperture from f/4 to f/5.6 halves the amount of light passing through the lens and halves the brightness of the image that falls on the image sensor.

Changing the f-number also changes the distance in front of or behind the focus point that appears to be in focus. The higher the f-number, the greater the distance in front of and behind the focus point that appears to be in focus; on the other hand, the lower the f-number, the shorter the distance in front of and behind the focus point that appears to be in focus. The distance in front of and behind the focus point that appears to be in focus is referred to as “depth of field.”

Photographing the Same Scene at Different Apertures

Changing the aperture changes depth of field.

High f-number (increased depth of field)

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  • The illustration is an artist's conception.
Depth of field: long
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Low f-number (decreased depth of field)

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  • The illustration is an artist's conception
Depth of field: short
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f-numbers

f-numbers change as shown below.

f-numbers

Raising the f-number one step is referred to as “stopping aperture down a step ” or “stepping aperture down an f-stop.” This halves the area of the aperture (or opening), halving the brightness of the image that falls on the image sensor. Lowering the f-number by one step is referring to as “stopping aperture up a step ” or “stepping aperture up an f-stop.” This doubles the area of the aperture (or opening), doubling the brightness of the image that falls on the image sensor.

If you are using a Nikon digital SLR camera, f-number changes in 1/3 steps; some models also support increments of 1 step and 1/2 step.

Sample Camera Displays

camera information display
camera information display

f-number:

Shown as f/4, f/4.5, f/5, f/5.6, etc.


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