Jay Sousa: Putting the focus on the f-stop

In the last Range Finder column, I discussed the basics of making a good exposure using the manual setting on your digital camera. This week I want to help you to use the tools of exposure, shutter speed, ISO and aperture or f-stops, to not only to make a good exposure but also as a creative tool.

Let's start with shutter speed. As I mentioned in my last column, the faster the shutter speed the better you will be able to freeze the movement of a fast-moving object. Let's use a bicycle race as an example. The racers are moving across your field of view at a speed of 30 miles an hour. You would need a shutter speed of at least 1/500 second to freeze the action. So, obviously the first thing you would do is set your camera to 1/500 second and then set your f-stop to make a correct exposure.

Now let's say that your ISO was set at 100 but at 1/500 second you were underexposed even with your f-stop opened up all the way. So let's raise your ISO to 200; this will give you one more f-stop of exposure. If this isn't enough, raise your ISO until you have an f-stop that will produce a perfect exposure.

You froze the action and your images are sharp and well exposed. But now you want to show how fast the racers are going by introducing some motion to create a sense of speed in your images. Let's do this by using a slow shutter speed of 1/60 second. To keep a good exposure, now you'll need to change your f-stop to a setting that is smaller, maybe f-11 from f-4 that you had with the 1/500 shutter speed that you used to freeze the action.

Now let's try a technique called panning. When we pan we are using an even slower shutter speed to create a sense of motion in the background but keeping the center of interest, in this case the bicyclist, sharp. Start with a shutter speed of 1/30 second. Again you will need to adjust your f-stop to maintain a correct exposure.

Now as the racers come by, move your camera along with them as you press the shutter release button. The trick is to match the speed of the bikes as they move across your field of view. This might take a few tries to make the shot. Play around with using slower shutter speeds as well. Try 1/15 of a second or even 1/8 of a second. The slower the shutter speed, the more abstract your image will look.

The f-stop control, in addition to letting the correct amount of light strike your digital sensor, also acts as a means of controlling how much of your image is in focus from front to back. This is called depth of field -- the smaller your aperture opening (f-22), the more depth of field; the larger your aperture opening (f-4) the less depth of field.

So what is the best depth of field to use? The quick answer is that it depends on what you are photographing and your creative vision for that image. For me, if I am doing a portrait, I want a larger aperture opening of f-4 because I want to throw the background out of focus to isolate the subject from the background. If I am making a landscape image, I want an f-stop of f-22 to keep as much of the scene in focus from front to back. So in this case we need to adjust our shutter speed and-or our ISO to keep a good exposure.

Your assignment for the week is to line up three apples on a table in your back yard and photograph the apples from front to back. Start with an f-stop of f-22 and focus on the middle apple, next try f-8 again focus on the middle apple, finally do the same thing using f-4. Don't forget to adjust your shutter speed to keep a good exposure throughout the three images.

I will be leading a fall landscape photography workshop in the Eastern Sierra on Oct. 21-23. Email me at jay.sousa@sbcglobal.net for more info.

This story was originally published September 24, 2011 at 2:07 AM with the headline "Jay Sousa: Putting the focus on the f-stop."