Many people have the impression that when they buy camera bodies with the new matrix or evaluative metering system there is no longer a need to understand exposure. While camera bodies of today do provide a more accurate exposure in a larger variety of lighting situation they are by no means foolproof. Evaluative or matrix metering does provide a more accurate rendition of tonal value, but even this metering methodology is not without inaccuracies in some situations. Even the best in camera meter which is found in the Nikon F5 is not perfect, but it does come close! It is up to the photographer to know what their camera meter will do in different lighting situations.

Spot Metering

Most of today's cameras offer spot metering, which can be an essential tool for Nature photographers. Handheld spot meters evaluate light in a "1" degree area, where as in-camera meters generally use a "2-3" degree area. In my experience the in camera spot meter works thus eliminating the need to carry another piece of equipment into the field.

The rest of this instructional will use the term "medium tone" to refer to 18% tonality.

Spot meters will make the metered area medium toned. Medium tone is just what it says. It is the middle tone between the darkest and lightest tones or colors on the scale. It is half way between the darkest color and lightest color, whether it is red, green, blue, or brown. This medium tone applies to all colors and includes white, gray and black.

There is no problem when the subject is medium tone as the camera will make it medium tone on film. Just point the spot meter at the subject, lock in the exposure, and press the shutter. At times it can be difficult to find a medium tone to meter and this is where the exposure problems begin.

Spot metering allows the photographer to choose an exposure so that they can place the tonal values where they want them. Slide film is capable of capturing five stops of light or tones. This allows the photographer to record two stops of light either above or below medium tone. So that you might get a feel for how this works, think of photographing snow. If you were to meter the snow and accept the in camera metering the white snow would then be 18% grey. The same holds true for darkest browns and blacks, only in this case they would be recorded lighter than their real tonality.

Since we know that our meters make everything middle tone, we can easily adjust the exposure by using exposure compensation. Think back to part one of this instructional, where we talked about stops of light. Stops of light are divided by your camera system so that a more exact exposure can be obtained. Stops are divided into either thirds or halves on the exposure compensation dial, depending on the body being used. After you master the tones and exposures you may wish to use 1/2 and 1/3 stops of light when making adjustments. This takes more practice when it comes to spot metering. As mentioned in Part I, each photographer should decide what they consider correct exposure to be.

White snow is two stops lighter than medium tone so by dialing in "+2" full stops of compensation we can now adjust our cameras to keep the snow in its proper tonality, but this will record the snow without detail. Black is at the other end of the exposure spectrum and by dialing in "-2" full stops we can keep our subject its true color - but - we once again lose the detail. In order to maintain the detail in the whites you would dial in "+1 1/3" stops. To maintain the detail in the blacks you would dial in "-2/3 to 1" stop exposure compensation.

But what about those tonalities that lie somewhere in between, that is, between medium tone and the lightest or darkest tones lies another tone? This tone is either 1 stop darker or lighter than medium tone and for this we add only one stop or subtract one stop. The tones are broken down into "1/2s" adn even to "1/3s" so that exposure can be recorded very accurately.

The only drawback to spot metering I have found is that it can take a few moments to evaluate the scene and dial in the appropriate compensation. As with everything, practice makes perfect. Spot metering works great for subjects that aren't moving fast. Landscapes, mammals, and macro are types of photography where I prefer to use spot metering since this technique does require a moment or two for the photographer to do the mental calculations.

Think back to Part One of this instructional, where we talked about stops of light. Stops of light are divided by your camera system so that a more exact exposure can be obtained. Stops are divided into either thirds or halves on the exposure compensation dial, depending on the body being used. After you master the tones and exposures you may wish to use ½ and 1/3 stops of light when making adjustments. This takes more practice when it comes to spot metering.

The only draw back to spot metering I have found is that it can take a few moments, especially when you are first using this metering modality in the field. As with everything, practice makes perfect. Spot metering works great for subject that aren't moving fast. Landscapes, mammals, and macro are types of photography where I prefer to use spot metering since this technique does require a moment or two for the photographer to do the mental calculations.

If you want to perfect your spot metering technique I highly recommend buying John Shaw's video on "Understanding Exposure". While this video was produced a couple of decades ago, I have not found a single source that demonstrates spot metering and exposure as well as this video. Shaw's images show the tonality, how he meters the image, and he goes in to the stops of light in a very easy to understand lecture. Arthur Morris has an extremely well-written chapter on spot metering in his "The Art of Bird Photography". Both sources provide excellent information in an easy to understand format.

Evaluative/Matrix

The next method I wish to mention was refined by Arthur Morris. After hours in the field he has become so familiar with the evaluative/matrix systems that he knows how the system will record tonalities on film in different lighting situations. Since this system uses a computer chip the results when used in the same lighting situations are reproducible. Mr. Morris has developed an exposure system based on what the computer chip does. This system is what I use and recommend for all bird photography. It is quick and very accurate, making it a great tool for capturing fast moving subjects like birds on film.

Since the Evaluative and Matrix metering system looks at the entire scene, not just the subject, it averages the tonalities in the scene. Dark backgrounds influence the meter and will usually overexpose for light or white subjects. Light backgrounds will usually cause the meter to underexpose for dark subjects. The quality of light also plays a part in how this system meters. Brighter conditions, light backgrounds and light tonality subjects will cause the meter to expose the subject properly. Medium backgrounds have the least effect on the meter, and if the subject is light or medium tone then no compensation is required.

Arthur Morris does include the basics of his metering method in his book "The Art of Bird Photography", but I prefer his exposure cards as they are the easiest way to learn the system since there are so many variations to be found in the field. Once you study the cards you will quickly see the pattern and it becomes the fastest system to use in the field and as accurate as any other exposure system of today.

You can find out more about the exposure cards in Ellen Anon's review this month. The cards can be purchased at www.birdsasart.com.

About the Images

Bison - Metered the shoulder and used 0 compensation.
Prairie Dog Trio - Metered the shoulder and used -1/3.

Editor's Comment: Let us know what you think! Please email the Editor to let us know your thoughts. Debbie is the Founder and Publisher for PhotoMigrations and would like to invite you to also visit her personal website located at Debbie Ferrell-Smith Nature Photography. You will be pleasantly surprised!.