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Exposure is one of three elements of PHOTOGRAPHY
It is called "Exposure" to give the film or sensor's surface the proper light through the lens. In other words, it is to give the proper light for "ISO sensitivity" to the film or sensor by using aperture and shutter speed. "ISO", "Aperture" and "Shutter speed" are called " Three Elements of EXPOSURE".
There are basically 2 kinds of exposure;
Standard exposure and Proper exposure.
"Standard exposure" is the value which light meter gives you. The photo with standard exposure appears to be looked by the human eyes."
Proper exposure" is determined by photographers intention, compensated from standard exposure. |
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Measuring methods of light meter
The measured exposure value depends on reflectance of photographing objects (color, brightness etc.) You can check if the highlights and shadows are within the dynamic range of film or digital camera sensor by measuring reflected light contrast but need to compensate the measured exposure value.
In contrast, the measured value of incident light measurement does not depend on reflectance of photographing objects or brightness of background because the light itself is measured which streams on the objects. However, this measurement can not be basically logically taken for distant object.
You need to select the measuring method of light meter tailored to the photographing situation. |
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| Reflected light measurement |
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Because reflected metering reads the intensity of light reflecting off of the subject, they are easily fooled by variances in tonality, color, 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 gray rendition of that object.
Subjects that appears lighter than gray will reflect excess light and cause them to record darker than they appear. Subjects that are darker than gray will reflect less light and result in an exposure that renders it lighter. |
| Incident light measurement |
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Because incident metering reads the intensity of light falling on the subject, it provides readings that will create accurate and consistent rendition of the subject's tonality, color and contrasts regardless of reflectance, background color, brightness or subject textures.
Subjects that appear lighter than middle gray to your eye will appear lighter in the finished image. Subjects that are darker than middle gray will appear darker.
Colors will be rendered accurately and highlight and shadow areas will fall naturally into place. | |
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Comparison of photographs between incident measurement by hand-held light meter and reflected light measurement of camera's built-in meter
When taking pictures of the subject with white and black background by measured value of light meter (hand-held light meter or camera's built-in meter), the photos below show the different results.Incident metering by hand-held light meter is not affected by reflectance of background. Accordingly, white appears white, and black appears black.
However, Reflected metering by camera's built-in meter receives the effect of reflectance.
The photo in white background is underexposed and black background is overexposed.
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| •Incident light measurement |
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•Camera's built-in light meter |
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Necessity of light meter for digital camera
While a histogram is the most convenient way to see how the entire scene will reproduce (or not), it really doesn't tell us the whole story. There's information about absolute subject exposure and lighting but it's difficult to interpret. Plus there's no feedback in terms of numbers that match your camera setting (i.e.f/stops) - that's the job of a light meter.
In addition, most camera manufacturers only give you an approximate representation of the subject histogram, because they realize the viewing window is too small to provide accurate detail.
Although there are some exceptions to this, Cameras that offer more information are more expensive and/or are designed for the slower paced studio environment where you have lots of time to analyze and reanalyze both lighting and exposure.
And don't be fooled into thinking you can determine exposure accurately on the LCD screens on the back of digital cameras. While they generally offer a fair representation of the image, they are most often low resolution and difficult to see, which makes them hard to use to judge subtle subject variation, as well as misleading when viewed under different lighting condition.
The best insurance for proper exposure is a good light meter |
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Digital retouching process
In today's digital age, although the technology behind photography is much more advanced, obtaining professional quality results still require the best techniques and tools.
Digital capture has a dynamic range and latitude roughly comparable to transparency film. What this means is if you are used to properly exposing transparencies, you are off to a good start. But if you are accustomed to the wider exposure latitude (extra margin of exposure error) that color negative film gave you, it is time to change your thinking.
Although it may seem that any miracle can happen in the digital darkroom, correcting a bad exposure has its limits. At first glance it may look like it is possible to make corrections, but upon closer inspection you may notice that image quality has suffered in addition, the time spent on the computer fixing a bad exposure will far exceed the amount of time it takes to get it right in the camera. |
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As an example, look at Figure 1. In this case the exposure was calculated by built-in light meter in camera which read the excessive amount of light reflecting off of the white background and averaged it with the subject lighting in an attempt to reproduce a middle gray value. This averaging caused underexposure of the image ("subject failure").
Figure 3 shows the same improperly exposed scene "fixed" in the computer.
For Figure 2 a handheld light meter measured the incident light falling on the subject to determine proper exposure, so Figure 4 looks great without any computer manipulation.
Although to some people images in both Figure 3 and 4 might be considered acceptable, when they are seen next to each other in Figure 5 it is clear that the "fixed" image is of much lower quality.
By using the computer software to "push" process the image it had to "stretch" the limited information and could not fill in or "fake" the missing data. This literally caused gaps on the range of tones as shown in the histogram.
Of course, higher digital cameras and digital backs will yield better results with some variations in proper exposure. And multiple exposure techniques as well as the use of RAW capture will allow you to effectively extend exposure latitude; although, once again these techniques will add additional computer processing time and require proper exposure control. |
Figure 1
Camera's Built-in Meter Exposure |
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Figure 2
Digitally Pushed Correction |
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Figure 3
Hand-held Light Meter Exposure |
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Figure 4
No Compensation Required |
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| Figure 5 |
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Using a camera's built-in TTL light meter, instead of a hand-held meter, will commonly cause over or underexposed areas in a high contrast scene.
