Nature and Photography Blog

Understanding Aperture, Fstops and Depth of Field

Alaska Sunset

Alaska Sunset

Learning Depth of Field is critical to great photography. Depth of field is the area in front of and behind your point of focus. Roughly 2/3 of depth of field extends behind the focus point and one third extends in front of it.

Most photographers use the program mode where the camera will select the depth of field for you. My goal on my instructional photo tours and workshops is to get people off program mode. How does the camera know how much of an area you want in focus? Don’t allow you camera to make this decision for you.

Magnification and aperture determine depth of field.

Magnification: Regardless of the aperture you select moving closer to your subject increases magnification and reduces the depth of field. Moving away from you subject increases depth of field since it reduces the magnification. Macro and close up photography for example requires more depth of field vs a wide angle landscape shot where you are standing farther away.

Aperture: is the size of the opening in the lens. When you press the shutter button a hole opens up which allows light to come in and hit your camera’s sensor. What aperture you set impacts the amount of light. The bigger the hole the more light comes in.

Shutter speed and aperture have an inverse relationship they work against each other.

Smaller hole = less light = more depth of field = less shutter speed.

Larger hole = More light = less depth of field = higher shutter speed.

Aperture is measured in F Stops. A photographer sets the F Stop to control the shutter speed and the depth of field.

The Common F Stops include

F 2.8, F4, F5.6, F8, F11, F16, F22 etc

I you change from one F stop to another it double of cuts in half the size of the opening in your lens. Keep in mind that a change in shutter speed from one stop to the next doubles or halves the amount of light that gets in also – this means if you increase one and decrease the other you let the same amount of light in.

Now you know where you hear the term opening up and closing down. It is referring to a change in the F stops which increases or decreases light.


One thing that causes a lot of new photographers’ confusion is that large apertures (where lots of light gets through) are given f/stop smaller numbers and smaller apertures (where less light gets through) have larger f-stop numbers. So f/2.8 is in fact a much larger aperture than f/22. It seems the wrong way around when you first hear it..

The higher the number the more area is in focus. So F16 would have a lot more in focus than F4. This is the opposite of what you would think. The reason why is it is really fractions F4 is Really F ¼ and F16 is really F 1/16

Selecting an aperture is often based on two variables.

a.) what area you want in focus?

b.) Conditions in the field: low light and wind etc.

Sometimes you may want more area in focus but the more depth of field the less shutter speed you can get. So you may have to compromise. Lets say you are photographing a flower and want to use F16 which would keep a large area in focus. If the light is low or it is windy you can’t afford to lose to much shutter speed or you will lose sharpness and the photo will be blurred.

I plan on writing about shutter speed soon.

Please consider joining us on a photo tour or workshop.

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