The "System"

This "system" provides accurate exposures guides for the most common lighting situations faced by photographers using transparency film: Normal or Low Light and Bright Sunny Days. This system is not "unique" or "special" in any way. It is the system used by almost all nature photographers (whether they know it or not). Although these guides are generally applicable to print films, because of the wider latitude (i.e., ability to provide proper exposure where the range and contrast of light is great) of print films, the compensation suggestions may not be great enough to provide for proper exposure for print films.

Two Simple Rules

Two simple exposure compensation rules to remember with slide film are "LO-DC" and "LC-DO."

In Normal or Low Light, and when the tone of the subject matter is Light, you need to Open up to ensure proper exposure. If the subject matter is Dark, you need to Close down to ensure proper exposure. LO-DC means Light Subject, Open Up - Dark Subject, Close Down

On a Bright Sunny Day, and when the tone of the subject matter is Light, you need to Close down to ensure proper exposure. If the subject matter is Dark, you need to Open up to ensure proper exposure. LC-DO means Light Subject, Close Down - Dark Subject, Open Up

These may seem not seem logical at first, but you need to remember that your camera exposure meter is calibrated to properly expose an 18% gray card (a medium tone subject). When you meter a subject lighter than 18% gray under Normal or Low Light, such as snow, the camera meter "tells" you how to expose the snow as if it were a medium tone subject. The resulting image of snow therefore looks gray! When faced with this situation and you are using slide film, you must compensate by opening up 1.5 to 2 stops so that snow is white (i.e., Light/Open).

The opposite is true. If shooting a dark subject under Normal or Low Light, such as a black bear, your meter will give you the proper exposure for an 18% gray card, turning the black bear into a gray bear (or at least a tone of black that is much lighter than the bear actually appeared). Because the subject is Dark, you need to Close down (i.e., Dark/Close).

On a Bright Sunny Day, the rules of exposure shift. Rather than attempt to explain this here, accept it as "truth" and experiment. You'll be pleased with the results. This exposure rule is often referred to as the "Sunny f/16 Rule." This means that on a Bright Sunny Day with few clouds in the sky, the proper exposure for a subject with front lighting is f/16 at a shutter speed closest to your ISO film speed. If I was shooting Fuji Velvia (ISO 50), the proper exposure would be 1/60th of a second at f/16, or a combination of shutter speed and f-stop equal to this (i.e., 125th at f/11). One note of caution, always avoid shooting on a Bright Sunny Day unless the subject matter or timing leave you with no alternative. The resulting images are generally not as good as ones taken under better lighting conditions (early morning, late afternoon or on cloudy days).

But My Meter Does Compensate!

At this time, no in-camera meter can automatically compensate for these situations. Whether the new Nikon F5 metering system will be able to handle these types of situations due to its unique design and use of a color meter is still up in the air (at the time this article was written, the test reports were not out on the F5's metering capabilities).

How Do You Open Up and Close Down?

So how do you "open up" and "close down?" You can change the shutter speed, the f-stop, or both. Let's go back to the snow scene. Your meter indicates that the proper exposure is 1/125th of a second at f/16. You determine that two stops of exposure compensation is needed. To "open up," you can: (1) change the f-stop to f/8 (f/8 allows two stops more light to reach the film than f/16); (2) change the shutter speed to 1/30th of a second (allows two stops more light); or (3) change the f-stop to f/11 (open one stop) and the shutter speed to 1/60th (open on stop), for a combination of opening two stops. To close down, you reverse the process.

Learning How to Find Medium Tone Subjects

In order to make this system work for you, you need to develop a level of experience regarding what is a Medium Tone subject under various lighting situations. Take a gray card into the field and take a meter reading of the card (be sure to watch out for any strong reflections of light off the card which can throw off the meter). Then place the palm of your hand in the same light as the gray card and take a meter reading of it. If you are taking proper readings, the reading off your palm should be one stop lighter than the gray card. If this works, start taking meter readings of various subjects in the field (in the same light) to help you "learn" what is a Medium Tone subject under those lighting conditions.

Experiment

If you know what a Medium Tone subject is, then you'll also know what Light and Dark tone subjects are by a process of elimination (i.e., well, that rock is lighter than Medium so it must be Light!). In addition, once you learn what a Medium Tone subject is, you can then experiment with this concept. As an example, if you are shooting a sunset and want the sky (generally a Light tone subject) to be darker than it is, you can set it as the Medium Tone for the image. This shift makes all Very Light subjects (the sun) in the image become Light, Light subjects become Medium, while at the other end, Very Dark becomes Very Very Dark. By understanding this relationship you can create images to match the mood you want to establish for the image.