If you have read the introduction to apertures, you should have a basic understanding of how the diaphragm in a camera lens works. In this section, you will learn in-depth about how to control f-stops in your pictures. You will also learn about shutter speeds, and how these work together to produce an exposure.

As I explained in A brief introduction to apertures, f-stops are the number values that tell you about how much light will reach the film. But as you may not know, f-stops also affect the depth-of-field in a scene. If you remember in the Depth-of-field section, I explained that the depth of field refers to the zone of focus in a picture. Apertures also have to do a great deal with the depth-of-field in a picture. Remember about how I said that the smaller the f-stop number, the more light reaches the film? Well, depth-of-field can be applied to that, but in a slightly different way. The smaller the f-stop number, the shallower the depth-of-field will be in the final image. That’s right, exactly opposite of light. For example, if the f-stop number is f/1.7, most likely anything that is not around the center of focus in a scene will be blurred out. However, if the f-stop number is f/22, almost every part of the scene will appear sharp and visible (not much light will reach the film, however).

Shutter speeds

In The camera, you learned that the shutter is the mechanism in a camera that opens and closes, allowing light to reach(or not reach) the film. You also learned that a shutter usually stays open for only a split-second. A shutter speed is basically the time the shutter in a camera stays open. If your camera can be adjusted manually, you have the option to set the camera at different speeds. If you are holding your camera (i.e. not using a tripod), it is common for the shutter to be open for about 1/90th of a second or higher, to avoid blur. Shutter speeds can be opened for as long as 5 hours to as short as 1/8000th of a second, but it all depends on what you are taking a picture of.

Let’s say your on a photographic assignment. Your goal is to photograph a fast-moving race car. When the car approaches, you quickly set your camera’s shutter speed to...2 seconds! When you look at your picture, to your upset, the car is a complete blur, and the image in ruined. This is an example of why it is important to set your shutter’s speed wisely. If you want to capture something as fast as a race car, setting the shutter speed to 2-3 seconds would not be a logical choice. However, setting the shutter speed to 1/2000th of a second would. Basically it ends up like this: The longer the speed, the more blurred moving objects will appear. The shorter the speed, the sharper the moving objects will appear. Motion is not all you have to worry about when adjusting shutter speeds, as you will learn.

Along with recording motion, shutter speed can also determine about how much light will reach the film, just like what apertures do. Remember that film is a very light sensitive material. The longer the shutter is open, the more light the film is exposed to.

Now that you understand about what shutter speeds and apertures are, you must learn about how these both work together to produce an exposure. Creating a good exposure is not possible unless you control the amount of light that would reach the film. This is basically set by adjusting the shutter speed and aperture so that they both are balanced. For example, if you are shooting indoors with a good amount of lighting, and your camera is being hand-held, you might set your camera to f/2.8 at 1/60 sec. If the image on film appears not too dark or too bright, that would mean that was a proper exposure. If the image appears to be too bright, it is overexposed. If the image is too dark, it is underexposed. Let’s say that we wanted to change the aperture setting (assuming that the setting above was a proper exposure) to f/5.6 at 1/15 sec. The image would appear almost exactly identical! The reason the exposure looked the same is because we set the aperture two stops smaller, and the shutter two stops slower. If you are feeling confused, do not feel bad, for exposure is one of the most complex issues in photography, and light meters help us a great deal. Remember that the best way to learn something is to try experimenting with it yourself, on your own camera, or on our virtual one.

That’s right. After all this talk about "correct exposures", you may not want to find out that that there is no such thing as it. Why? Because of the fact that there are so many different lighting conditions. The real correct exposure is all a matter of what your preferences are. It is an artistic decision. And that is why you must experiment!

Now that we are finished with this lesson, we can continue on with learning about composing a scene properly, and also about how to experiment with photography in Composition and experimentation: the basics.