Part 1b - Exposure Is Everything. What is the camera's meter saying to me? (continued)

Well, how did the "mind" photography go?

Before I show you the answers to this exercise, I'll spend a few sentences laying some important ground work. We are talking about exposure. Exposure is the total amount of light that strikes the film in traditional photography or the light sensor in modern digital cameras.

Three exposure possibilities exist.

1. Too little light strikes the film or sensor -- producing an underexposed (dark) final picture.
2. Too much light strikes the film or sensor -- producing an overexposed (light) final picture.
3. Just the right amount of light strikes the film or sensor -- producing a final picture that's very close (in all aspects of color, density, contrast, etc.) to the original scene.

When a camera is in any of its "auto modes" (full auto, aperture preferred or shutter preferred), it's the built-in light meter that takes over to determine how much exposure (light entering the camera) is just enough to create the perfect picture. Unfortunately, most photography newcomers (and far too many "oldcomers") fail to recognize the assumptions the light meter is making, and how to interpret the information that the light meter ultimately returns to the photographer.

Now, let's look at the results of our experiment.

The answer to each of the three questions in my last post (What does each final picture look like?) is the same. Each final picture is gray. In fact, each picture is the same middle shade of gray:







So, what does this mean? For one thing, it means your camera's light meter and "auto" exposure processor are working perfectly and doing just what they are designed to do.

When I teach in a Photo 101 setting and conduct this same exercise, I invariably receive these answers:

1. The picture of the white card is white.
2. The picture of the gray card is gray.
3. The picture of the black card is black.

Think about those student answers. If the resulting pictures were actually white, gray and black, that would mean the camera's light meter (and internal processor) were able to distinguish objects in the real world, understand which picture element was your subject, and translate that information into a perfect exposure. Well, that's not the real photographic world (yet). If it were possible, photographers would be lugging around more computing power than they would be willing or capable of carrying. The light meter in your camera does not understand your shooting conditions or have the ability to read your mind.

It does, however, have one solitary mission in life: It accurately measures the light entering the camera's lens and relays this measurement to the camera's exposure processor. The processor then uses this information to adjust the settings of the shutter and aperture (in auto modes) to allow just enough light to strike the film or sensor to produce a "middle gray" image. Every time.

There's an important note to add about this "middle gray" thing. Your camera's meter "sees" in terms of black and white densities. So the results of this exercise would have been exactly the same if we had used three different shades of a color for our original cards -- for example, a very light green, a middle shade of green and a very dark green. The final prints would have all rendered the various green cards as the same middle green shade (see example below):






Let's equate this exposure process to a more real world situation that you have probably encountered. I'll use a picture from my New Jersey home where winter snow storms are common. (Sun worshipers please substitute a brightly lit beach scene. The results are similar.)



The scene of your home and landscape covered in fresh snow is straight from a fairy tale and worthy of capturing for posterity. Photographers who don't understand the light meter's capabilities and resulting measurements will invariably be disappointed when their final picture looks similar to the image below:



This typical result is UNDEREXPOSED -- not enough light was allowed to strike the camera's sensor. Is the camera broken? What was the camera thinking? If we could listen in on the digital conversation in the camera it would go something like this.

• "WOW! Where did all that light come from?
• But "no problem".
• I'll measure the amount of incoming light.
• Then I'll set a shutter speed and aperture setting that will produce an exposure that renders the scene as middle gray."

And it did just that. The snow in this scene was exposed to render that factory-set, middle gray shade of color. Unfortunately, this middle gray is not true to reality (unless, of course, you were trying to simulate a moonlit snow scene. But that's another can of worms for later discussions). As you know, snow is an extremely light shade of gray (almost pure white).

Please don't think of this situation as hopeless. The opposite is the truth. Knowing what the meter is trying to accomplish is the starting point for all of your photographic heroes. It also places you well on the path of becoming the best photographer you can be.

So, now that we understand what the camera's meter is built to do, the post titled Part 4 will help you use this knowledge to learn exactly what's so special about your camera's specific "middle gray". Then you can begin taking control of your exposures and gain the confidence to know that "what you see is what you get". Photographic WYSIWYG.

Hope this series is helpful to you. As always feel free to send along your comments and suggestions.