In our last discussion we talked about the physical settings (aperture, shutter speed and ISO) that went into creating our one ideal exposure for a given scene. Hopefully you did the exercises and are now comfortable with changing your cameras settings, and have wrapped your mind around the relationship that exists between the 3 settings. Today we are going to look more closely at aperture.
Different aperture settings let in different amounts of light. An f-stop of f/2.8 lets in a lot more light than an f-stop of f/22. The smaller the setting value, the larger the aperture opening, the more light. As you may have observed in your experiments, there are many different combination’s of setting that all give you an equal exposure, or equal amount of light. However, each setting has its own unique impact on the image that is produced. Understanding this unique impact is the first step that you will take in helping to create the image that you see in your mind!
Depth of Field
Creatively, the aperture setting that you choose controls the Depth of Field in an image. Depth of Field is simply the portion of an image that appears acceptably sharp. When you focus your camera on your subject there will be an area in front of, and behind, your subject that is going to be acceptably sharp. This section that is acceptably sharp is your depth of field. Why should you care? I mean wouldn’t you always want everything to be in sharp focus? Like all things in life, there is always a trade off, and this is no different. For example, at f/2.8 you let in a lot of light, but you may only have a depth of field of a few inches, while at f/22 you might have an infinite depth of field. You can use this knowledge to influence how your images turn out. Using an aperture of f/2.8 will give you a very shallow dof, and you can use this to really isolate your subject. Using larger aperture values, such as f/22 are great for when you want to have a large portion of your image sharp, such as when doing landscape photography. When setting up a shoot, one of your first questions should be “What do I want for a depth of field?”. Are you trying to isolate one part of a scene, such as a single flower in a meadow? If so, then chance are that you want to shoot with a small aperture setting (such as f/1.8, f/2.0, f/2.8, etc). Or are you trying to capture the entire scene, such as the reflection of a mountain and clouds on a lake? In this case you want to shoot with a large aperture setting, such as f/22 to capture the details in the entire scene. What if you really aren’t trying to do either? Well, that is when the old saying “F/8.0 and be there” is the guideline to follow!
Exercise
Take a book/magazine and open it up on your kitchen table. Now take a picture of it with your aperture at f/2.8, and then take the same picture at f/22. In the image taken at f/2.8 you will only be able to read a few of the lines of text from your book. The rest of the text will be blurry, getting blurrier the further it gets away from your focal point. In the image taken at f/22 you will be able to read much more of the text. The area that is reasonably sharp will be much larger! It is this effect that will allow you to help call attention to your subject. Play around with the angle at which you shoot the book, and see how that plays into the resulting images. What happens when you keep the camera parallel to the book?
Summary
As you can see the aperture setting that you choose controls the Depth of Field in your image, and this has a huge impact on how your photos comes out.