Exposure (part one)

In previous posts, I talked about lighting as it applies to the subject of your photos. Today, let’s take a step back and talk about how to properly record that light in the final picture, whether taken with a digital or traditional camera. A traditional SLR (single lens reflex) camera is similar to a SLR digital camera. You have settings for shutter speed, lens opening (or aperture) and a focusing ring (unless you have an auto-focus (AF) lens). In some cameras, you can set the auto- focus feature to manual. This is handy if you want creative control.

SLR cameras also have light meters built in. Some use needles to indicate proper exposure and some use other methods like lights that indicate the same thing. Regardless of how it is accomplished in your camera, it is there to help you expose your photos properly. And while the auto-focus, auto-expose systems work reasonably well in most lighting situations, you will still want to know some basics about light and how your camera sees and records the light. “What is going on in that camera’s sensors?” is something you have probably asked yourself many times.

Shutter speeds and lens openings combine to ensure that enough light is coming into the camera, but not too much or too little. F-stops (lens openings)range from 1.2 or 1.8 to 16 or 22, depending on the speed of your lens, which is another topic for another time. 16 or 22 is the largest number, and it corresponds to the smallest lens opening. Likewise, 1.8 is the smallest number, and it corresponds to the largest lens opening. Confused yet?

The terminology of this is that you “stop down” your lens when you go from a larger lens opening to a smaller lens opening, and you “open up” when you do the reverse. In sunny Arizona, you will want to “stop down” (allow less light in through the lens). In Pennsylvania, where it is cloudy most of the time, you will want to allow more light in through the lens, or “open up” the lens.

There is a relationship between the shutter speed (how fast the shutter opens and closes) and the f-stop (or lens opening). This means that for every one step change in lens opening, there is twice as much light allowed through the lens. If you go from a setting of 8.0 to a setting of 5.6, for example. The opposite is also true: going from 5.6 to 8.0 reduces the light by half.

The same is true for shutter speeds. Shutter speeds range from 1 second up to 1/3200th of a second and everything in between. A shutter speed of 1/60th of a second is twice as fast as a speed of 1/30th of a second. You can visualize what a shutter does like this:
Close your eyes. Now open your eyes and count out “one-thousand one”, and then close your eyes again. Open your eyes again and count out “one-thousand one, one-thousand two” and close your eyes. This is what a shutter does.

Now close your eyes, open them for just a blink, then close them. This represents a fast shutter speed. If you are looking for something in the dark, you will need to keep your eyes open a long time. In bright light, your eyes can see things clearly in a short amount of time. This is the same for a camera. In low light, you need more exposure of the film to the light. In bright light, you need less time to accomplish the same exposure to the film. I’m getting a little long winded here, so I will continue with this discussion later.