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Home > Learn > Exposure 101 > Reflected Light Meters
Using Reflected Light Meters, Part One
Metering Tools Metering and Light Meters Metering is all about taking the wide range of tones and lighting conditions in the real world and translating them into the more limited range of tones in a photograph. Metering is the key to good exposures. The human eye can see a huge range of tones from light to dark in sun and shade all at the same time. A camera, whether digital or film, can't capture the whole range of tones that the human eye can see in a single exposure (although several different exposures of the same scene can be combined after the fact in the computer to approximate what the eye can see). Lots of choices need to be made for you to end up with an exposure that you like. Light meters (and other tools) will help you get the exposure you want. Modern light meters are absolutely, whiz-bang amazing and do highly accurate job, provided you understand what they are (and aren't) designed to do. As long as you know how to talk their language and make them do their tricks for you, they are an excellent tool in most situations to arriving at an excellent exposure decision. Reflected and Incident Light Meters There are two primary kinds of photographic light meters. Reflected light meters measure the intensity of the light that is reflected off the subject. For that reason, you usually point a reflected light meter at the subject. The meter in your camera is a reflected light meter. Incident light meters measure the intensity of the light that is falling on ("incident to") the subject. Therefore, you usually point an incident light meter at the light source. There is an incident light meter with the characteristic white dome in the center of the photo at the top of this page. Both meters do the same thing, they measure the intensity of the light. Light meters can't "see", they just measure light intensity. Just like a sound meter that measures the intensity of the sound but can't tell if the sound is coming from a symphony or a freight train, a light meter measures the intensity of the light, but it can't tell (for the most part) if the subject is red, green, blue, orange, or pink with purple polka dots, or if the light source is a light bulb, flashlight, or campfire. Both kinds of meters assume your subject is "middle gray" in tone (about half way in between black and white), or that the tones in your scene average out to a middle gray. When a light meter gives you a suggested exposure, it is not giving you an exposure that will work for all subjects of all colors and tones. If your light meter says "f/16, and 1/100 second at ISO 100", what it is really telling you is this: "f/16 and 1/100 second at ISO 100 is a good exposure in these lighting conditions if your subject is middle gray in tone. If your subject is lighter or darker than a middle gray, you will need to make some adjustments from this recommendation." Light meters have to be calibrated to some standard, so it's a good thing meters are calibrated for a middle gray tone since most subjects are in between black and white in tonality. If meters were calibrated for white or black subjects, exposure would be even more complicated than it already is. In Camera vs Hand Held Reflected Light Meters Reflected light meters are found in your camera and are also available as a separate, hand held meter. In camera meters are the most common. Large format landscape photographers don't have a meter in their camera, so many of them use a spot-meter, a reflected light meter that measures a very small area in a scene so the photographer can meter individual tones in the larger scene. Most cameras have a built in reflected light meter. By changing the metering pattern you can meter most of the scene in your viewfinder (center-weighted average), the central area in your viewfinder (partial area metering), or just a tiny spot in the center of your viewfinder (spot metering), just like a large format landscape photographer. In camera reflected light meters have the advantage over hand held reflected light meters because they meter through the lens (TTL) and any light robbing accessories. Teleconverters, extensions tubes, filters, and other other accessories reduce the amount of light that hits the film/digital sensor. A hand held reflected light is oblivious to these accessories and will give you an incorrect meter reading unless you allow of the amount of light that each accessory is costing you. If your 1.4x teleconverter is costing you one stop of light, you need to add one stop of light to what the hand held reflected light meter is telling you. Your TTL meter measures the light after it has gone through your lens and accessories, so no compensation needs to be made for the accessories. Your Reflected Light Meter's Love Affair with Middle Gray Tones Your reflected light meter loves middle gray so much that it does its best to turn anything you meter into a middle gray tone. You can prove this to yourself with gray, black, and white subjects. Just be sure when you meter your subject that the meter sees only the subject, and not any other tones in the scene. In the following photo, I photographed a black, gray, and white calibration target. I moved in close and metered the gray center section and locked in that exposure so it wouldn't change. Then I backed up and photographed the whole calibration target and included some of the background.
Calibration Target #1, Metered for the Gray Center Section In the above photo, the calibration target looks just like it does in real life. In the following photo, I did exactly the same thing, except I moved in close and metered the black section on the left, locked in the exposure, and backed up to take the picture.
Calibration Target #2, Metered for the Black (Left) Section The meter did its best to turn the black section (in real life) into a middle gray section (in the photo) and everything else ends up lighter than in real life. In the following photo, I did exactly the same thing, except I moved in close and metered the white section on the right.
Calibration Target #3, Metered for the White (Right) Section The meter did its best to turn the white section (in real life) into a middle gray section (in the photo) and everything else ends up darker than in real life. To see how well the meter did it's job, look at these "color patches".
The left patch is an enlargement of part of the gray section of the calibration target from the first photo. The center patch is an enlargement of part of the black section from the second photo. The right patch is an enlargement of part of the white section from the third photo. The meter did a pretty good job of making all three a "middle gray" in tone. Three things are obvious from the above photos. 1. If you meter something middle gray in tone, everything in the photo ends up looking pretty much like it does in real life. That's why a lot of photographers will meter an 18% gray card or the gray section of a calibration target (like the one above), and use that meter reading as the basis of their exposure when they photograph their scene. 2. If you meter something darker than middle gray, everything looks lighter in the photo than it does in real life. The darker the subject you meter, the lighter the photograph of the scene. 3. If you meter something lighter than a middle gray, everything looks darker in the photo than it does in real life. The lighter the subject you meter, the darker the photograph of the scene. Why Your Meter Gets Fooled How does this apply to the real world when you aren't photographing calibration targets? Your camera meter's desire to make everything middle gray (or "medium toned" in the world of color) leads it astray when your subject isn't medium toned, or if all the tones in a scene don't average out to medium in tone. In the following photo, my camera was set to manual metering mode, and the aperture to f/16 to give me enough depth of field to keep everything sharp from the foreground rocks to the distant mountains. I set the metering pattern to partial area metering so the camera would only meter the central 10-15 percent of the frame. I zoomed in on the blue sky and sunlight peaks and set my shutter for a good exposure. Then I zoomed back to include the whole scene and took the picture. The ISO was set to 100 for maximum image quality, and the camera was on a tripod so the photo wouldn't be blurred during the 1/5 second exposure.
Long's Peak and Nymph Lake, Rocky Mountain National Park The photo came out just like I wanted it to with the warm light on the peaks, the reflection in the water, and the contrast of the very dark evergreens in the shade. While I was taking the picture, the camera meter was screaming at me: Too Dark! Too Dark!! (I'm sure your meter talks to you too!) The meter was seeing all of the dark tones in the center of the image and it wanted to make them medium toned. I decided to let the camera meter have its way. The photo would look awful, but it would be a nice demonstration of what happens when camera meters go astray. So I turned the shutter speed dial until the meter was happy (1.6 seconds, 3 stops more light than the above photo) and took this picture.
Long's Peak and Nymph Lake, Rocky Mountain National Park As expected, the meter did its best to make the large, central area of the frame average out to a medium tone, but the mountains and sky are now three stops overexposed and seriously washed out ("burned out" in photo terms). I could digital combine the two photos so I have some tonality in the trees (which is another reason I took more than one exposure), but I rather like the dramatic, high contrast lighting of the original image. Exposure Compensation Due to your meter's fascination with creating medium toned subjects, you need to do some exposure compensation when photographing subjects that are lighter or darker than a medium tone. Exposure compensation simply means adding or taking away light from what the camera meter tells you. For light subjects, you add light and for dark subjects, you take away light. Just repeat this phrase a few times: "Add light to make light". This may seem counterintuitive. Your pupils shut down in really bright light so it is tempting to say. "Wow, that's really bright snow, I should take away light." But we are talking photography, so "Add light to make light." If your subject is medium toned, do what the meter tells you. If your subject is light in tone, add a stop of light to what the meter tells you by opening you lens up a stop, or using a shutter speed one stop longer. IF you are photographing a very light tone, add two stops of light. If you are photographing a dark tone, subtract 1 stop of light from what the meter tells you. If you are photographing a very dark tone, subtract 2 stops of light. For example, if you are photographing a field of wheat that is ready to harvest (which is about one stop lighter than a middle gray), and the meter says f/11 at 1/250 second, add one stop of light by changing the f-stop to f/8 or by changing the shutter speed to 1/125 second. If you are photographing evergreen trees (which are darker than middle gray) and the meter says f/11 at 1/60 second, subtract one stop of light by changing the f-stop to f/16 or the shutter speed to 1/125 second. Here's the standard exposure compensation advice when metering the subject with a reflected light meter:
But in my experience, subtracting that much light for dark subjects results in subjects that are usually too dark for my taste. So here is the exposure compensation that I recommend:
Tonality Exercise The best way to get a feel for subject tonality and exposure compensation is to experiment. Pick a bright sunny day with clear blue northern skies (southern skies if you are south of the equator) and green grass. If you have an 18% gray card (and having one is a good idea), bring it along since it is a good standard reference for medium gray. Find something red and something yellow. That way you will have the basic red, yellow, green, and blue colors covered, plus a gray card. Fill the frame with each subject, being careful not to cast your shadow on the smaller subjects when you get close. Take 5 pictures of each subject in one stop increments from 2 stops less than the cameras recommends up to 2 stops more. The exposure series will be as follows: -2, -1, 0, +1, +2. Your camera should have an exposure compensation dial (check the manual) which will tell you how many stops you have subtracted or added to the recommended exposure). You may have an LCD screen that looks something like this.
Electronic Camera LCD Screen The shutter speed is at the upper left (1/500 second), the aperture at upper right (f/8), the white balance at center left (AWB = Auto White Balance), the ISO setting at center right, and the exposure compensation across the bottom. In this illustration, the exposure compensation is +1, one stop more than the exposure recommended by the camera meter which will result in a subject one stop lighter than a medium tone. After you have taken 5 photos of each subject, you should end up with a group of photos that looks like this.
Exposure Compensation Tonality Test Chart For my tonality test, I photographed a gray card (top row), red cloth, blue sky, yellow bowl, and green grass. The left hand column is all of the -2 exposure compensation photos, no compensation in the middle column photos, and +2 compensation in the right column. Compare your subjects to the photos and decide which exposure of each subject looks the most like the real life subject. For my photos, it came out like this: Gray Card: 0 compensation Take note that blue sky, depending on elevation, atmospheric conditions, and particulate matter in the sky can easily range from 2 tops darker to two stops lighter than a medium tone. Green grass, depending on the time of year and direction of the sun can vary from -2 to +1 or even lighter. The more you experiment with exposure compensation, the better you will get at deciding how much compensation each subject needs to create a photo that looks like the subject in real life. Breaking Loose, Creative Exposure Compensation Once you have a good handle on exposure compensation, mix things up a bit. Sometimes the best photos come from making the subject look lighter or darker than it did in real life. Pros do it all the time. You can make any subject as light or dark as you want. Consider these two photos, taken the same evening from the same location (with different focal length lenses). The second photo was taken much later than the first photo and it was much darker out. I tried a variety of exposures for both photos. The exposure I liked for the first photo is much darker and more dramatic than it was in real life. The exposure I liked for the second photo is just the opposite, much lighter than the original scene.
Sunset, St. Joseph Lighthouse, Michigan
Evening, St. Joseph Lighthouse, Michigan Experiment with exposure compensation. Play with the light! Don't worry. The exposure police won't come and take you away for making a sunset darker and more dramatic, or lighter and more ethereal. Get out there and have fun! Be sure and read Part Two of this article, Choosing the Right Tone to Meter. More Information The most detailed information about metering, camera meters, and other metering tools is in my book, Digital Photography Exposure for Dummies. December 22, 2010 |
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Copyright © Jim Doty, Jr. All rights reserved. |
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