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Aperture and Depth of Field

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#1 Photographa



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Posted 12 May 2014 - 01:31 PM

In this post we’ll teach you how your choice of aperture will affect the depth of field in your photos. Let’s start by defining some terms -

Aperture is the opening in the lens which can be dilated or constricted to change the amount of light that hits the sensor of your camera. As your F-number increases, the aperture opening gets smaller and smaller.


Depth of Field is the depth of the section of your photo that’s in focus. In any photo, objects from x meters to x+ymeters will be in focus. That y is the depth of the area that will be in focus. Any object in front or behind the area in focus will be blurred.


Depth of field will always be more shallow when you photograph something very close to the camera lens. If you put your camera right up to an object and focus on it, you can have the tiniest sliver in focus and have the rest of your photo will be an out-of-focus blur. As the camera gets farther from the object in focus, the area in focus (the depth of field) will become larger. This is assuming a constant aperture.


As you increase the size of your aperture (by using smaller f-stop numbers), depth of field will become more shallow, and as you constrict the aperture to make it smaller your area in focus will become larger and larger.


By joining what you know about depth of field being affected by camera proximity and aperture size, you can begin to control the depth of field in your photos.


For example -

  • If you want to photograph a model that stands far away from you and you want to blur the background behind her, you can use a larger aperture to achieve a more shallow depth of field so that you can have a sharp focus on her body but not behind it.
  • If you want to photograph a model that stands very closely to you and you want to blur the background behind her, using a very large aperture could prevent you from having her entire body in focus because the depth of field would be too shallow. You’d be safe using a slightly smaller aperture so that her whole body can be in sharp focus, and because your camera is near her your depth of field would still be shallow enough to blur the background.

Keep in mind that as you change your aperture, you’ll want to compensate with your shutter speed in order to keep your photos properly exposed. If you shoot in A mode (Aperture priority) on your DSLR,  your camera will automatically adjust for the optimal shutter speed as you change your aperture.

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