Friday, 31 October 2008

Using Reflected-Light Meters

Once you have set the proper film or camera speed or sensitivity (this is characterised by a numerical value followed alphabets ‘ISO’. To further understand ‘The Photographic Process and Film Sensitivity’ students may visit Perry Sprawls at his website) by on your camera or meter, you are ready to make the exposure-meter reading. With a reflected-light meter (in camera or handheld), point the camera or meter at the subject. The meter will measure the average brightness of the light reflected from the various parts of the scene. With an in-camera meter, a needle or diode display in the viewfinder or an LCD display on top of the camera will tell you when you have achieved the proper combination of lens and shutter-speed settings. If the camera is fully manual, you will have to set both the aperture and shutter speed. Automatic cameras may set both shutter speed and aperture; or they may set just one of the controls, leaving you to set the other.

If you're using a handheld meter, read the information on your meter and set the camera controls accordingly. An overall exposure reading taken from the camera position will give good results for and average scene with an even distribution of light and dark areas. For many subjects, then, exposure-meter operation is mostly mechanical; all you do is point the meter (or camera) at the scene and set the aperture and shutter speed as indicated. But your meter does not know if you need a fast shutter speed to stop action or a small aperture to extend depth of field. You will have to select the appropriate aperture and shutter combination for the effect you want. There will be other situations where either the lighting conditions or the reflective properties of the subject will require you to make additional judgements about the exposure information the meter provides, and you may have to adjust the camera controls accordingly.

A reflected-light meter reading is influenced by both how much light there is in the scene and how reflective the subject is. The meter will indicate less exposure for a subject that reflects little light, even if the two subject are in the same scene and in the same light. Because reflected-light meters are designed to make all subjects appear average in brightness, the brightness equivalent to medium gray, they suggest camera settings that will overexpose (make too light) very dark subjects and underexpose (make too dark) very light subjects.

Although reflected-light meters are influenced more by the largest areas of the scene, the results will be acceptable even when the main subject fills the picture but it's still of average reflectance (neither very light nor very dark). However, what happens if a relatively small subject is set against a large dark or light background? The meter will indicate a setting accurate for the large area, not for the smaller, but important, main subject. Therefore, when the area from which you take a reflected-light reading is very light or very dark, and you want to expose it properly, you should modify the meter's exposure recommendation as follows:
• For light subjects, increase exposure by 1/2 to 1 stop from the meter reading.
• For dark subjects, decrease exposure by 1/2 to 1 stop from the meter reading.


Please remember that since reflected metering reads the intensity of light reflecting off of the subject, they are easily fooled by variances in tonality, colour, contrast, background brightness, surface textures and shape. What you see is often not at all what you get. Reflected meters do a good job of reading the amount of light bouncing off of a subject the trouble is they don't take into account any other factors in the scene. They are merciless in recording all things as a medium tone. Reflected measurements of any single tone area, for instance, will result in a neutral grey rendition of that object. Subjects that appears lighter than grey will reflect excess light and cause them to record darker than they appear. Subjects that are darker than grey will reflect less light and result in an exposure that renders it lighter.

Selective Meter Readings

To determine the correct exposure for higher contrast scenes with large areas that are much darker or much lighter than the principle subject, take a selective meter reading of only the subject itself. How do you do this? Move the meter or camera close to the subject. Exclude unimportant dark or light areas that will give misleading readings. In making close-up readings, also be careful not to measure your own shadow or the meter's shadow.

Selective meter readings are useful for dark subjects against a bright background like snow or light sand, or for subjects in shade against a bright sunlit background. There is also the reverse of this: The subject is in bright sun and the background is in deep shade. In all these situations, your camera has no way of knowing which part of the scene is the most important and requires the most accurate exposure, so you must move in close so the meter will read only the key subject area. For example, if you want to photograph a skier posed on a snowy slope on a bright, sunny day, taking an average reading of the overall scene will result in underexposure. The very bright snow will overly influence the meter and the reading will be too high. The solution is to take a close-up reading from the skier's face (or a piece of medium-toned clothing) and then step back the desired distance to shoot the picture. Some cameras with built-in meters have an exposure-hold button or switch to lock the exposure setting when you do this. This technique is useful anytime the surroundings are much brighter or darker than your subjects.

Landscapes and other scenes with large areas of open sky can also fool the meter (See picture on the left, originally posted to Flickr as Rays of sunlight by Spiralz). The sky is usually much brighter than other parts of the scene, so an unadjusted meter reading will indicate too little exposure for the darker parts of the picture. One way to adjust for this bias without having to move in close is to tilt your lens or meter down to exclude the sky while taking your meter reading. The sky will probably end up slightly overexposed, but the alternative would be to find a different shooting position excluding most or all of the sky. There are also graduated neutral density floaters that work well in such situations. A neutral density filter absorbs all colours of visible light evenly, and you can position a graduated filter so that the darker portion is at the top of the image where it will darken the sky without affecting the ground below. Incidentally, some built-in meters are bottom-weighted to automatically compensate for situations like this, so check your manual.

Bright backlighting with the subject in silhouette can also present a challenge. With the light shining directly into the lens or meter, aiming the meter into the light can cause too high a reading. If you don't want to underexpose the subject, take a close-up reading, being especially careful to shade the lens or meter so that no extraneous light influences the reading.

Substitute Readings

What if you can't walk up to your subject to take a meter reading? For instance, suppose that you're trying to photograph a deer in sunlight at the edge of a wood. If the background is dark, a meter reading of the overall scene will give you an incorrect exposure for the deer. Obviously, if you try to take a close-up reading of the deer, you're going to lose your subject before you ever get the picture. One answer is to make a substitute reading off the palm of your hand, providing that your hand is illuminated by the same light as your subject, then use a lens opening 1 stop larger than the meter indicates. For example, if the reading off your hand is f/16, open up one stop to f/11 to get the correct exposure. The exposure increase is necessary because the meter overreacts to the brightness of your palm which is about twice as bright as an average subject. When you take the reading, be sure that the lighting on your palm is the same as on the subject. Don't shade your palm.

Another subject from which you can take more accurate and more consistent meter readings is a KODAK Grey Card, sold by photo dealers. These sturdy cards are manufactured specifically for photographic use. They are neutral grey on one side and white on the other. The grey side reflects 18% of the light falling on it (similar to that of an average scene), and the white side reflects 90%. You can use a gray card for both black-and-white and colour balance. Complete instructions are included in the package with the cards.

Handling High Contrast

How do you determine the correct exposure for a high-contrast scene, one that has both large light and dark areas? If the highlights of shadow areas are more important, take a close-up reading of the important area to set the exposure. With colour slide film, keep in mind that you will get more acceptable results if you bias the exposure for the highlights, losing the detail in the shadows. In a slide, the lack of detail in the shadows is not as distracting as overexposed highlights that project as washed-out colour and bright spots on the screen. If you are working with black-and-white film, you can adjust the development for better reproduction of the scene contrast, particularly in highlights.

But what if the very light and very dark areas are the same size and they are equally important to the scene? One solution is to take selective meter readings from each of the areas and use a f-number that is midway between the two indicated readings. For instance, if your meter indicates an exposure of 1/125 second at f/22 for brightest area and 1/125 second at f/2.8 for the darkest area--a range of six stops--set your camera 1/125 second f/8. This is a compromise solution, but sometimes it is your only choice short of coming back another day or changing your viewpoint, and the composition of the picture, to eliminate the contrast problem.

Using Spot Meters

Perhaps the best solution when you need a selective meter reading is offered by the spot meter. Handheld averaging meters generally cover about 30º, while handheld spot meters typically read a 1º angle The angle of spot meters built into the camera are usually wider, about 3 to 12º. The biggest advantage of a spot meter is that is allows you to measure the brightness of small areas in a scene form the camera position without walking in to make a close-up reading. Since a spot meter measures only the specific area you point it at, the reading is not influenced by large light or dark surroundings. This makes a spot meter especially useful when the principal subject is a relatively small part of the overall scene and the background is either much lighter or darker than the subject. Spot meters are also helpful for determining the scene brightness range. See picure on the left by Joseph Dickerson (the image has all rights reseved: Photos © 2004, Joseph A. Dickerson)

A spot meter can take more time to use since it usually requires more than one reading of the scene. This is particularly true when the scene includes many different bright or dark areas. To determine the best exposure in such a situation, use the same technique described previously for high-contrast subjects: Select the exposure halfway between the reading for the lightest important area in the scene and that for the darkest important area in the scene. Bear in mind, though, all films have inherent limits on the range of contrast they can accurately record. Remember too, you can sometimes create more dramatic pictures by intentionally exposing for one small area, such as a bright spot of sunlight on a mountain peak, and letting the dark areas fall into black shadow without detail. Spot meters are ideal for such creative applications. See picture on the left for creative control of light and careful planning of exposure after taking multiple spot meter readings by Dave Johnson. Also, note the subject and its environment... use of a spot meter usually is convenient in such situations.

Using Incident-Light Meters

a. Set ISO/ASA of film being used.
b. Hold light meter in front of scene with the sphere pointed at the camera.
c. Depress centre button.
d. Needle will move to a reading.
e. The reading is measured on the foot-candle scale.

Depending on the lighting conditions, there are two settings that can be utilized - the Red Arrow setting (when the High Slide is inserted in the slot below the sphere) is used outdoors in bright light and the Black Arrow setting (High Slide is removed) is used in lower light circumstances.

f. Move dial to Black Arrow setting when High Slide is not used so the number lines up with the corresponding number on scale.

Or

g. Move dial to Red Arrow setting when High Slide is used so the number lines up with the corresponding number on scale.
h. Shutter speed scale
i. Aperture scale

Please note that above image and text has been taken from http://paulturounetforum.com/2007/09/24/nature-of-light-and-artificial-light/. I have tried not to tamper with this text nor the image. In fact you may want to visit the above website.

Moving on, to use an incident-light meter, hold it at or near the subject and aim the meter's light-sensitive cell back toward the camera. The meter reads the amount of light illuminating the subject, not light reflected from the subject, so the meter ignores the subject and background characteristics. As with a reflected reading, an incident reading provides exposure information for rendering average subjects correctly, making incident readings most accurate when the subject is not extremely bright or dark.

When taking an incident-light reading, be sure you measure the light illuminating the side of the subject you want to photograph, and be careful that your shadow isn't falling on the meter. If the meter isn't actually at the subject, you can get a workable reading by holding the meter in the same kind of light the subject is in. Because the meter is aimed toward the camera and away from the background light, an incident reading is helpful with backlit subjects. This is also the case when the main subject is small and surrounded by a dominant background that is either much lighter or darker.

The exposure determined by an incident-light meter should be the same as reading a gray card with a reflected-light meter. Fortunately, many scenes have average reflectance with an even mix of light and dark areas, so the exposure indicated is good for many picture-taking situations. However, if the main subject is very light or very dark, and you want to record detail in this area, you must modify the meter's exposure recommendations as follows:
• For light subjects, decrease exposure by 1/2 to 1 stop from the meter reading.
• For dark subjects, increase exposure by 1/2 to 1 stop from the meter reading.


You will notice that these adjustments are just the opposite from those required for a reflected-light meter. An incident meter does not work well when photographing light sources because it cannot meter light directly. In such situations you will be better off using a reflected-light meter or an exposure table.

If the scene is unevenly illuminated and you want the best overall exposure, make incident-light readings in the brightest and darkest areas that are important to your picture. Aim the meter in the direction of the camera position for each reading. Set the exposure by splitting the difference between the two extremes.

Actual measuring

Foot Candle meters are the most commonly used meter for video. These meters display the amount of light striking them on a scale calibrated in foot candles, from 0 to 500 and are not dependent on any other factors.

In order to get an accurate reading the meter needs to be placed immediately in front of the subject facing the light source to be measured. The easiest way to take the key, fill, and back light measurements is to do them one at a time, with the other two lights turned off. Start with just the key light on, position the meter in front of the area of the subject struck by the key light. Aim the meter at the key light and note the number of foot candles. For example, if it reads 100 foot candles. Then next, turn on just the fill light and take another reading facing the fill light. If our intended lighting ratio is 2:1, then the fill light should read about 50 foot candles.

Now, turn on just the back light and take its reading. The back light should be somewhere between 50 and 150 foot candles, depending on the effect desired. The final step is to re-measure the key, fill, and back light positions with all the lights on. This is important since where the illumination from the lights overlaps the intensity increases. Adjust the intensity of the lights as needed to maintain the desired lighting ratio.

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