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Sorry to keep bouncing around. Hopefully this is the last time. I will not be updating this blogger blog any more.

Depth of Field

Depth of field or DOF, is a term used to specify the area of a scene that is in focus. A “shallow depth of field” has the subject sharp in focus, but the rest of the foreground and background is out of focus. The background and foreground appear soft. This is a great technique for getting your subject to stand out from the background. Take a look at this picture. You can see how I’ve made the background flowers out of focus so that subject flower stands out more.

Here is an example of where I didn’t do a great job separating the subject from background. I wanted just the first tulip to be the center of focus, but all the background is in focus too, and it’s distracting:

There are three things the affect the size of your Depth of Field: Focal length, aperture, and distance from the subject. I will go into the technique more later, but to summarize:

• Focal Length: The more zoom, the shallower the DOF
• Aperture: The wider the aperture (small F-Number) , the shallower the DOF
• Distance from subject: the closer to the subject, shallower the DOF.

The Basics - Aperture

Aperture is one of those photography terms that intimated me at first. It sounds quite technical, and even the units, F-Numbers, don’t make a lot of sense. Changing your aperture is a very powerful tool to a photographer, and there are many reasons why you’d chose a certain value, however, it again all comes down to light. In combination with shutter speed, aperture controls the amount of light hitting your image sensor. The more light, the brighter your image, the less light, the darker your image.

Technically, aperture refers to the size of the opening in the lens. Take a look at the example below. The top image is a wide or large aperture (lots of light), while the bottom image is a smaller aperture (just a small amount of light).

The other hard to grasp part of aperture is the numbering system. Aperture uses F-numbers or F-stops. It seems counter intuitive to me, however, the smaller the number, the larger the opening. So in the pictures above, the top lens might have an aperture of f/2 while the lower image has f/16. A trick I use to help me remember how F-numbers work was given to me by my photography professor… “think about inflating a cartoon bike tire. If you inflate it with a lot of pressure, the hole in the middle will get smaller” More pressure = tighter aperture = higher F-Number. Not sure if that helps you, but it works for me.

These images are all shot keeping the shutter speed constant and just adjusting aperture (which will cause them to be under/over exposed).

Overexposed with wide aperture: 1/10 sec, f/5.6

Proper Exposure with medium aperture: 1/10 sec, f/11

Underexposed with small aperture (big f-number): 1/10 sec, f/22

Aperture also has another effect on your images beyond how bright or dark your image is. After all, why would you need 2 ways to control this, shutter speed and aperture. What aperture does is also change the amount of your image that is in focus. This is referred to as the depth of field. I’ll cover depth of field in a later post, however, to illustrate the effects, take a look at the three images I’ve shot below.

Exposed properly, but with different aperture/shutter speed combinations, so you can see the depth of field effects.

½ sec, f /22 (all 3 quarters are in focus) – Slow shutter speed because aperture is small. This lets in enough light.

1/10 sec, f/11 (Center quarter is in focus, but back is out of focus, and most of front is out of focus) – Faster shutter speed because less light is needed when aperture is larger.

1/40 sec. f/5.6 (center quarter is the only one that is in focus) – Even faster shutter speed because aperture is all the way open.

This was another resource that I found helpful if you want to learn more:

http://www.photoaficionado.com/situationroom/aperture.html