You have a vision in your mind and want to stimulate others to see the same concept through storytelling. This is how exposure can assist you in capturing the moment and relating it via a photographic image. To tell a story using photography is an art form which takes time and practice to achieve. This blog reference an article in "Expert Photo Techniques" published by Shutterbug magazine, http://www.shutterbug.com and written by Moose Peterson, http://www.moosepeterson.com/blog/.
Exposure, it's not what we see, it's how the camera sees things. Our eyes can see more tonal range and light than any camera available today. Take for instance, our eyes and brains can take in approximately 20 stops of light, whereas, the camera can only render about 5 stops. Consider this; we look at items, be it a mountain landscape or a building. We perceive this as an object of creation. It invokes an emotion within us only as we see it. That emotion needs to be related to others and elicit a similar emotion or reaction, we need to tell the story of what we saw. We do this by taking a photo and making the image tell the story to those who see it. Composition, Exposure and Depth of Field combine to bring out an inspiring and emotional image. I will take one element of this equation, Exposure, to help you bring out the best in your photography.
So how do we achieve proper exposure to tell a story of what we see? Let's take a look at what features we have within the camera that will help us deal with proper lighting or exposure.
Light, an element of telling a story.
Most DSLR's have a highlight warning we call "Blinkies". They flash to let you know that some portion of the photo is overexposed. In order to see the blinkies, you must turn on the "Highlight Warning" in your cameras settings display options. Once turned on, they will show what areas are overexposed so you can make an adjustment. Another way to tell is the photo is overexposed, is to look at the histogram. If the histogram is bunched up on the right side, it is overexposed.
Why is this important? When viewers look at art, their eyes generally go to the brightest areas of the canvas (think of your print as a canvas). If the photo has washed out areas, that is what the viewer will see first. Should this be the case, you must ask yourself a couple of questions. Does the overexposed areas draw attention away from the image and if so, does it create a negative impact to the story? For instance, you are taking a shot of a beautiful beach in Hawaii, you set up, take the shot and the sky is washed out and the histogram is full right.. Most likely it will be distracting and probably not relate the story as you saw it.
Lack of detail, an underexposed image.
Remember what I mentioned about our ability to see light? In this case, a balance of light in both the highlights and shadow areas is a necessity to tell a story. It is how you want the viewer to see the story as you saw it. An underexposed image will increase the contrast The way to tell if it is underexposed is to look at the histogram, if the graph is bunched up on the left, there is a loss of detail in the shadows. This may be what you want how you want to display the image, such as a silhouette. There is no right or wrong in what you produce, it is how you saw the photo in your mind.
Sometimes you have to make sacrifices. Allowing the shadows to go dark or black may give you the richness in the highlights that just make a statement. There are ways to create detail in both shadows and highlights. Bracketing is one method for which you can post edit the image for both. HDR is software you can use to render the bracketed images into one image revealing both shadow and highlight detail. Some software can provide tools to dodge and burn, as in the days of film processing. This is a good solution, but one in which takes a lot of time and patience to perfect.
The use of Neutral Density (ND) filters or Graduated ND filters is another way to assist in good exposures. ND filters restricts the amount of light to the sensor, thus making the exposure time longer and allowing for the shadows. Again, you need to get familiar with their use just as you did with you camera. The Graduated ND, or Grads, allow an area of the image to have a reduced amount of light through the lens. These are great for enhancing a sky or clouds. They come in different types and stops. There is the hard edge and split grad. The hard-line has a dark area in one half of the filter, the other half is clear glass. The graduated is dark in one half and gradually goes to clear, there is no distinct line. Manufacturers make them in varying degrees of density, such as .6 or 2 stop, .9 or 3 stop and so on, so check them out before you buy them.
So, how does exposure tell a story?
There is no right or wrong way to exposure, it is how you relate a perception. Bright areas bring the viewer into the image, whereas dark areas tend to add contrast. Communicate with your camera to tell a story and let the viewers decide what they see in your image. Take for instance, a cloudy sky on an ordinary day. If you overexposed the sky, it can look washed out, which may say the weather is improving. On the other hand, take the same conditions and underexposed the sky. What it may be saying now is the weather is getting stormy and eerie. Have a vision in mind in what you are shooting and expose for what you want to say to your audience. Remember, it's you story, tell it like you imagine it through imagery, not words. Exposure can be your best asset or your worst nightmare.