Aperture (Exposure Series Part 3 of 5)

 Myfotoguy series on exposure part 3 of 5
 
Parts 1 and 2 discussed aperture and how the opening controls how much light is passing through. This article will cover the effects the aperture setting has on your image.
 
Review of Aperture and f-numbers
The size of the opening light travels through. A larger aperture means a larger opening; a small aperture means a small opening. The aperture is set using and f-number, sometimes called an “f-stop”. The numbering is counter intuitive because the larger the number, the smaller the opening. For example, f/22 has a much smaller opening than f/8.

The range of f-numbers follows a standard sequence with each number being half as bright (allowing half as much light to pass) as the previous one. A typical aperture range:

f 1.4; f 2; f 2.8; f 4; f5.6; f 8; f 11; f 16; f 22; f 32

If you change aperture from f-8 to f-5.6 you will gain one stop more exposure.

 

Effect of Aperture Size
Tree on a hill at f/16 Using a small aperture of f/16 allowed me to have everything in focus. From the frost covered grass in the foreground to the tree at top of the hill.
 
Aperture not only controls the light as an element of the exposure triangle, it also affects depth of field. Larger f-numbers produce a longer depth of field, allowing objects at a wide range of distances to all be in focus at the same time. Smaller f-numbers producer a shorter depth of field and less objects are in focus at the same time.
 
 

Depth of Field (DOF): How much of the scene is acceptably sharp in the image. It is how much of the scene is in focus. Large DOF means more is in focus, and small DOF means less is in focus. Sometimes you will hear photographers say “increase your depth of field”. What they are saying is that more of the scene should be in focus. You may also hear something opposite, such as “limit your depth of field to isolate the subject”.

DOF is most often said to be controlled by the Aperture.
  • Small f-numbers mean small (shallow) depth of field. Less of the image is in focus.
  • Large f-numbers mean large (deep) depth of field. Most of the image is in focus.

However, there are other factors that determine it besides aperture, such as:
  • The focal length of the lens (mm setting)
  • The distance between the subject and lens
  • The distance between the sibject and the background. 
For more information, see Online DOF calculator.

Which aperture setting should I choose?

Creative decisions will drive you to make an aperture choice.

If you’re taking a portrait in the park, or a flower in a field you may want the background to be blurred out to isolate your subject. In this case you would use a larger aperture (smaller f-number). Don’t simply dial in the smallest you can, you will want to experiment so that the intended parts of the image are sharp, while the background is soft. Distance to the subject and the focal length (mm setting) of your lens will also play a roll.

Purple flower at f/4 Purple flower at f/4.

If you’re taking a picture of a broad sweeping landscape, you may want as much of the image to be in focus as possible. In this situation you would use a smaller aperture (larger f-number)

Remember, aperture is one of the points in our exposure triangle. When you change the aperture, something else will need to change as well.
 
Aperture Priority
Aperture Priority is a semi-automatic mode. It allows a photographer to choose the aperture, and the camera will decide which shutter speed to use (sometimes ISO for cameras with an Auto ISO function).
 
Examples
Aperture Gallery

I've uploaded several examples to my gallery with notes explaining why I chose the aperture that I did.  Some of the images I simply posted the aperture setting.
 
You can visit the gallery HERE.
 
Please leave comments you may have. Also, if you would have chosen a different aperture I would be interested in hearing what you would have done, and reasons for it.

 
Conduct some experiments with your aperture and try some new things today. Then come back here and share your experiences in the comments below.
 
 
 
Articles in this series:
Part 1 - The Exposure Triangle
Part 2 - Stops, Values, and Sensitivity
Part 3 - Aperture
Part 4 - Shutter Speed
Part 5 - ISO

 
 

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