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Thursday, November 28, 2013

Introduction to Photography Exposure Terms – Part 2: Aperture

By Marc B

Last week we introduced beginners to shutter speed. This week (in Part 2 of the Introduction to Photography Exposure Terms), we’re introducing aperture.  
Using these two settings effectively, along with ISO settings, are key factors in creating the type and style of photograph you want. Think about the outcome you want and adjust your settings. Experimentation is the best way to learn what works, and most importantly, what works for you. So start shooting!

Aperture

There are two reasons to adjust aperture settings. These are, to control the amount of light in your photographs, and creating your desired depth of field in each shot.
Light
The aperture or ‘f stop’ refers to the opening inside a lens that controls how much light passes through the lens to the sensor.  In most lenses this is variable so the photographer can control the light with a high degree of accuracy, choosing if they want a brighter or darker photograph.
The widest aperture of a lens is usually written on the front the lens, and is usually shown as, 1:2.8. This means that the largest aperture on the lens is f2.8. 
On some zoom lenses it may be expressed as something similar to, 1:3.5-4.6. This means that at the widest focal length of the lens the largest aperture is f3.5 and when you zoom all the way in, the largest aperture will be f4.6.  The different representation of the aperture on a zoom lens is because the lens itself absorbs light as it is extended or ‘zoomed in’.
Depth of Field
Controlling the area of apparent sharpness in an image is referred to as the depth-of-field (dof) in an image.  A large aperture (which is achieved by selecting a small number ie. f2.4) will give a shallow depth of field to an image, and a small aperture (which is achieved by selecting a large number ie. f22) will give a deep depth of field.
In the graphic below the relative sizes of the apertures are shown.  At f22 the image will have apparent sharpness from front to back.  At f1.8 the image will have a narrow band of sharpness, or a shallow depth of field.

Examples
The first image is shot with a large aperture of f2.8 and you can see how the depth of field drops off quickly and the image loses sharpness.
 
The second image was shot with a small aperture of f22 and the depth of field is now very deep and there is detail a lot further back into the image.
 

 
Keep in mind that if you want the entire image to be sharp you need to use a small aperture (choose a large ‘f stop’ number).  If you want to achieve a shallow depth of field, use a large aperture, such as f2.4 or f1.8.
Experiment and have fun!
Next week, Part 3 of our ‘Introduction to Photography Exposure Terms’ will be on ISO.

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