Monday, December 31, 2007

Technique (Exposure)- The 18% Gray Card

Getting the correct exposure can be difficult in some situations, especially where the subject or the background is light or dark. The 18% gray card will help if you can use it, such as when you are taking a picture of a stationary subject.

An 18% gray card (may not be 18% gray on the screen and the white border is not part of the card).

Meters in cameras are set up to make everything an 18% gray. This is a standard in photography. Many subjects are about this color. If you point your lense at a white subject and it fills much of the frame, perhaps a white flower, and you use your camera's meter to set the exposure, the meter will try to make this flower 18% gray and the picture will be underexposed (the meter closes down to make the white subject gray). Likewise, the meter will try to make a black or dark subject, like a black bear that is really black (some are shades of brown), 18% gray and the picture will be overexposed. The following paragraphs explain how to use it and a way to use substitutes you always carry with you or that are around you.

The 18% gray card is just that- it is a card that is 18% gray. Some other items have been made 18% gray and are of a different material that will withstand field conditions. To use it, put it in the same light as your subject (gray side up) , fill your frame with it (be careful not to throw a shadow on it unless you plan to take your subject in the shadow- the card must be in the same light as the subject)(also, be sure to fill the frame with the card if you are not spot metering because a light or dark background can change the meter reading when the multiple metering setting is going to read these light or dark backgrounds), and check the exposure reading your camera's meter gives you. This will be the proper exposure. It is that simple! Even so, you may wish to bracket the exposure (overexpose and underexpose) by 1/2 stop because some people prefer a slightly darker exposure and some a lightly lighter exposure.

Sometimes it is difficult to carry the card with you everywhere you go or one tends to get lazy and not want to do so. What can you do to make things easier? Well, we'll use something we carry with us all of the time, check the exposure relative to the gray card, and use this other item as a substitute card. I use the palm of my left hand because, like the American Express Card, I carry it everywhere I go (I really don't carry an American Express Card, but the jingle is appropriate). In addition, it is usually exposed when I'm taking a picture. Why the left hand? I am right handed. So, I hold my left hand's palm so it is framed by the viewfinder (or screen on a digital camera) and check the meter reading holding the camera in my right hand and pressing the shutter release halfway down to get the reading. Obviously, a left handed person would use the other hand. Here is what you do. Take a meter reading from an 18% gray card. In the same light take another reading from the substitute object you will use (again, I use my left hand's palm). Unless you are the right color of brown or something similar (you lucky devils) or you always carry something you can meter which reflects light of a similar color as an 18% gray card, your object will give you a different exposure. Note the difference. For example, if you use your palm and your skin is lighter in color than an 18% gray color, the camera's meter will show less exposure. Why? The meter wants to make that lighter colored palm an 18% gray so it will give you a meter reading that lets in less light than an 18% gray card. To make things easy, let's say your palm's reading is 1 stop lighter than an 18% gray card. You now use your palm to take future readings. However, when you use it the camera's meter is going to give you a reading that is 1 less stop than an 18% gray card, so when you then point the camera toward the subject it will underexpose the picture by one stop. You have to open up one stop from your palm's reading to get the correct exposure. The opposite would be true of a person whose object is 1 stop darker than an 18% gray card. They would have to close down 1 stop to get the correct exposure. Be sure to remember the object you are using as a substitute. Your right palm may be lighter or darker than your left!

I know. This sounds like a bunch of correcting to use a substitute. However, all you have to remember is how much you have to open or close down to get the correct exposure and the object you use as the substitute. If you can't remember, just figure the exposure compensation needed again one time during the day and you will likely remember it for the pictures you will take for the rest of the day [or week, month, year, etc. if you have a better memory -mine lasts about 3 minutes (just a poor joke; here's another- I might start using my gray hair as a substitute because it may be similar to a gray card)].

There is a way to estimate the correct exposure when you don't have your substitute available (I hope I always have mine!). As I noted earlier in the article, there are many objects that will give you the same or similar reading as an 18% gray card. To learn how to judge this, take your gray card reading and point it at various objects in the same light to compare the readings. You will see the ones that give the same reading. If you do this enough, you will begin to get a feel for the subjects that give you the same reading. Grass and green trees (not those that are reflective due to leaf coatings) tend to give similar readings as does the gray color of the bark of some trees. Even clothing that is the correct color can be good (then you can have your favorite shirt or pants for photography). You could purchase a camera bag or similar object for photography that you carry (manufacturers have figured out that they can make photography gear in a color that gives you the same reading). Do you have a favorite place you like to take photos? Find the objects that give you the same readings and use them in the future. However, remember that some factors can affect your readings. If that gray tree gets wet the meter reading may change. Likewise, the favorite pants may fade in the wash and get lighter in color. Will a hand lotion or a clean versus a soiled hand change your palm reading? It is wise to take a meter reading from a gray card and compare it to your substitutes once in a while (a dark soil on your palm may change the reading from a light soil, such as white sand). You can do this will a palm with hand lotion on it or soiled to compare the readings. Do you tend to use something else on that palm that may change the reading? Compare your palm with that substance on it to the gray card also.

There is another way to get the proper exposure during a sunny day called the Sunny f16 rule. We'll explore this in another post.

1 comment:

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