Understanding Depth of Filed (DoF) is essential for creating visually interesting photographs. Knowing how to control what’s in focus and what’s artistically blurred, gives you a the ability to take those creative shots. Three things determine what’s sharp in any photo: aperture, focal length, and focus. However, to make this a truly 101 post, let’s focus on aperture only this time and see how aperture determines DoF.
“An aperture is a hole or an opening through which light travels.” (Wiki)
Aperture can be tricky to grasp but once you grasp it, it will give you a tremendous creative control over your photos. If you are not yet fully comfortable shooting in a full manual mode, you can still control your aperture by shooting in Aperture Priority mode. In Aperture Priority mode, you choose the aperture and the camera software chooses the shutter speed and ISO based on its own calculations of the available light to make sure you get correct exposure.
For most Nikon camera, Aperture Mode is labeled as “A” on the camera dial, for Canon users, it’s mostly “Av”. If you are shooting in manual mode, than you know that every time you change aperture setting, you need to change the shutter speed and ISO to get the correct exposure.
The smaller the aperture number = the shallower DoF = the less of your photo will be in focus.
For the photo bellow, I focused on the mug, my aperture was set to very wide aperture (f/2.8 )to artistically blur everything that was in the background. If I had any items in the foreground, they would be blurred just as leaves in the background are. My focus was on the mug and everything that was in front of it or behind it, is not in focus. This is called shallow depth of field.
Now, notice how DoF changes in the following photo. My aperture was changed to a large number f/13 (smaller aperture) to get a deeper DoF and get the most of the leaves in focus. I did not move my camera, my focus was still on the mug, but with a simple aperture change, my depth of field suddenly expanded and more of the image is in focus. This means that
The bigger the aperture number = the deeper DoF = the more of your photo will be in focus.
If you look at the shutter speed numbers, for the first photo, I went with a faster shutter speed (1/320 sec.) because I did not need shutter speed to allow more light in because the wide open aperture (f/2.8) already did that. For the second photo, smaller aperture (f/13) was allowing less light in and I had to compensate that with a slower shutter speed (1/20) to get a similar exposure.
- Shooting with wide aperture (e.g. f/2.8) allows a lot of light in and at the same time narrows your depth of field (less in focus); you need a faster shutter speed (1/500 sec.) because you already have a lot of light.
- Shooting with small aperture (e.g. f/16) allows in less light and deepens DoF (more in focus); you need to compensate for the loss of the light with a slower shutter speed (e.g. 1/15 sec.) which also brings in increased movement blur.
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