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Introduction to Light Meters
The spot meter allows precise readings to be made of small areas of the scene. Its narrow field of view measures light reflected from as small as a 1-degree circle. Any number of areas can be measured to create a set of values for a particular scene, this enables the photographer to determine the most suitable lighting arrangement and exposure settings that will produce the desired result.
In-Camera Spot Meters
Although a number of advanced SLRs offer spot metering capability, the metering angle is directly related to the focal length of the camera lens in use. Every time the lens is changed, the effective spot meter angle changes. With a normal lens in use, the spot-metering angle may be 15° or more. A hand-held 1° spot meter consistently allows the most selective measurement of distant subjects as well as small areas in the scene.
Advantages of Reflected Spot Measurement
A spot measurement is ideal for special situations including measuring distant subjects, backlight, extreme brightness range, highly reflective surfaces, or when an incident meter cannot be positioned directly in front of the subject. Reflected spot measurements of an 18% gray midtone, or an average of significant shadow and highlight measurements, allow the photographer to make an exposure that will record detail, tonality and accurate color.
The flash meter measures the brilliant and instantaneous burst of light produced by electronic flash sources and displays the correct aperture settings. Flash meters usually measure the incident light falling on a subject, however some meters also measure reflected light as well. Many flash meters take in to consideration the effects of available light.
Color Temperature Meters
A color temperature meter measures the color quality of ambient light, the light from electronic flash, or a combination of both.
The meter analyzes the color characteristics of the light source(s) exposing the subject, and then displays the required filtration to color balance the scene for the film being used, if any, as well as color temperature in degrees Kelvin.
Color temperature meters usually include calibrations for daylight and tungsten films.
Color temperature meters may not provide accurate readings for light sources with narrow band spikes and depressions in their light distribution. Sodium vapor, metal-halide, and fluorescent lamps are examples of light sources that are difficult to measure. Color-bracketed test exposures are therefore recommended to verify that the recommended filtration is correct.
Color Measurement of Ambient Light
Ambient light refers to a continuous source of light falling on the subject, such as daylight, tungsten or other sources.
If the ambient light originates from only one source, accurate measurements are easily made.
However, if lights from multiple sources illuminate the subject, color measurements are more complicated.
||When the light consists of a single color temperature, the meter should generally be held facing the main light source and as close to the source as possible.
||When the ambient light comes from multiple light sources with different color temperatures, each light source should be measured and the appropriate color correction filter sheets used.
||When ambient light and electronic flash are used together, the meter should be pointed at the flash. The required filtration that is required will be indicated.
When using shutter speeds that are lower than the flash synchronization setting, the meter will show the modified filtration that is needed for proper color balance.
When light-balancing filtration is indicated, it is preferable to use gelatin-type filters in front of the light fixture(s), rather than the camera lens. Keeping the optical path free of filtration avoids problems caused by dust, etc. on the filter(s). Also filter factors need not be taken into account.
Illustrations & copy adapted courtesy of Mamiya America Corp.
Sekonic Professional Division. Total Exposure Control with Hand-Held Metering
Incident vs. Reflected. © 2002