Monday, May 10, 2010

Depth of Field

What is Depth of Field?
When looking at the photos you may have noticed that sometimes an entire image is in sharp focus all the way from foreground to background, while other images are only in sharp focus for part of the image but the rest is blurry. The term Depth of Field refers to the part of the photo that is in focus.


An image with shallow Depth of Field has only a limited part in focus. Portrait photographers like to create this type of image with the subject nice and clear and the background very blurred. This draws the viewer’s eyes to the model and eliminates distractions.


An example of an image with a deep Depth of Field would be a landscape that shows flowers in the foreground, a lake with sailboats in the middle and mountains in the background with all parts of the scene in focus.

What determines Depth of Field and how can one control it? The aperture setting of the lens has a direct relationship to the Depth of Field in the photo. The aperture setting are labeled with f-stop numbers. A large number like f-16 is for a smaller opening. An f-stop with a small number like f-2 denotes a larger opening. At first it may be confusing that the small number is a large opening, but after a while you will get used to it.


When the lens is set to a large aperture such as f-2.0 or f-2.8 the Depth of Field in the photos is rather shallow. But when an aperture such as f-16 or f-22 is used the resulting image will have a deep area of Depth of Field. For a midway setting, f-8 is often chosen.

Understanding the f-stops or aperture settings on your camera is essential to mastering depth of field. After a person learns to master the camera settings, their photos will show an improvement.

If your camera is always set to the green rectangle for FULL AUTO or P for PROGRAM you will not be able to master Depth of Field. To set the aperture, place the dial on AV for APERTURE PRIORITY. (It is a good idea to read you camera manual to learn the specifics of you camera model.) After the dial is set to AV you have some freedom to choose an f-stop. The reason you have some freedom and not total freedom is because there is a relationship between aperture and shutter speed. When you use a small aperture such as f-22 there is less light entering the camera so the shutter speed must be reduced so that enough light enters and you get the proper exposure. In AV mode the camera’s onboard processors will calculate and set the shutter speed for you. In M or MANAUL mode you can set both aperture and shutter speed.

If we go the other way and set a wide aperture like f-4 then a lot of light is entering the camera so we need to compensate by increasing the shutter speed. Again the camera’s onboard processors will calculate and set the shutter speed for you.

Canon cameras also have a setting on the dial for Depth of Field mode. The setting on the dial is marked A-DEP which lets the photographer select on one spot in the foreground and one spot in the background then the camera assures that everything between the two is in focus.

The focal length of the lens and the camera-to-subject distance also affects Depth of Field but I will not get into that now.

So now you should take a few minutes to read your camera manual and then go grab your camera and experiment with different f-stops and see how the Depth of Field in the image changes. Don’t be afraid to make mistakes. Have fun and be creative.