Exposure Metering
Compendium
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Exposure Metering Compendium
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Table of Contents
1
External Exposure Meters Still as Important as Ever ............................................................... 4
2
Light in Photography ............................................................................................................. 9
3
2.1
Color Rendering ..................................................................................................................... 10
2.2
Color Temperature ................................................................................................................ 10
2.2.1
Color Temperature Throughout the Day ....................................................................... 11
2.2.2
Color Temperatures of Light Sources ............................................................................ 11
2.3
Light Characteristic – Hard and Soft Light ............................................................................. 12
2.4
Luminous Intensity – the Inverse-Square Law ...................................................................... 13
2.5
Influence of Light Shapers ..................................................................................................... 15
2.6
Light Direction ....................................................................................................................... 16
White Balance .................................................................................................................... 17
3.1
White Balance in Analog Photography .................................................................................. 17
3.2
White Balance in Digital Photography................................................................................... 18
3.2.1
Automatic White Balance .............................................................................................. 18
3.2.2
Manual White Balance with Presettings ....................................................................... 18
3.2.3
Manual White Balance with Gray Reference ................................................................ 18
3.2.4
Manual White Balance with White Balance Filter......................................................... 19
3.2.5
White Balance under Mixed Lighting Conditions .......................................................... 19
3.2.6
White Balance and Color Profiling................................................................................. 20
3.3
4
5
6
White Balance in the Digital Camera..................................................................................... 21
Fundamentals of Exposure .................................................................................................. 22
4.1
The Exposure Triangle ........................................................................................................... 22
4.2
F-Stop .................................................................................................................................... 23
4.3
Shutter Speed ........................................................................................................................ 23
4.4
Shutter Speed / F-Stop Combinations ................................................................................... 24
4.5
ISO Sensitivity ........................................................................................................................ 24
How does an Exposure Meter Work? ................................................................................... 25
5.1
Standardization to 18% Gray ................................................................................................. 25
5.2
Exposure Value (EV) .............................................................................................................. 25
Measuring Methods ............................................................................................................ 26
6.1
Reflected Light Measurement ............................................................................................... 26
6.1.1
Average Metering .......................................................................................................... 27
6.1.2
Center-Weighted Average Metering ............................................................................. 27
6.1.3
Spot Metering ................................................................................................................ 27
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6.1.4
Selective Metering......................................................................................................... 27
6.1.5
Multi-Segment Metering, Matrix Metering .................................................................. 28
6.1.6
2-Point Metering ........................................................................................................... 28
6.1.7
Substitution Measurement with Gray Card .................................................................. 28
6.1.8
Reflected Light Metering Methods of Cameras ............................................................ 29
6.2
7
3
Incident Light Measurement ................................................................................................. 29
Flash Exposure Metering ..................................................................................................... 31
7.1
Adjusting Studio Lighting – Lighting Contrast ....................................................................... 31
7.2
Triggering the Flash Unit with the Camera ........................................................................... 33
7.3
Triggering and Metering with the Exposure Meter............................................................... 33
7.4
Combining Flash and Continuous Light ................................................................................. 33
8
The Zone System ................................................................................................................. 35
9
The Histogram .................................................................................................................... 36
10 Controlling Contrast ............................................................................................................ 37
11 Recommended Reading ...................................................................................................... 39
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4
External Exposure Meters Still as Important as Ever
One of the most frequently asked questions is: “Is a handheld exposure
meter still necessary at all for digital photography? My camera is
capable of matrix metering, center-weighted metering and spot
metering – what more could I possibly need? I see the image results
immediately at my display and in the histogram, and I correct exposure
there. If necessary, I get rid of any image recording flaws later at my PC
with image processing software. Why should I work with a museum
piece like the one my grandfather used?”
In order to answer this question, we first have to look at what differentiates digital photography from
analog photography. Basically, the only thing that has changed is the recording medium – an image
sensor is used instead of film. Up to the point in time at which the image is actually recorded,
everything’s the same, and the same composition rules and optical laws apply to both analog and
digital photography. Photography doesn’t become digital until the data from the sensor are
converted by means of an analog-digital converter.
And the curse or the blessing of this new technology begins no later than precisely at this time. In the
case of analog photography, each recording costs real money for film and developing, in addition to
which the results don’t usually become visible until a week later. This necessitates well planned
image composition, deliberate and careful work, and a limited number of recordings due to the costs
involved. In the case of digital photography, a recording is assumed to have no costs at all, and it’s
available immediately. However, these positive aspects often lead to a careless attitude and an
overwhelming inundation of images.
In the case of analog photography, flawed images can be corrected to some extent in the lab. This
applies to digital photography too, except that a computer with image processing software is used.
The same specialized knowledge and the same amount of time and effort are required in order to
correct flaws which occur during image recording. However, correction options for achieving good
results with a poor recording are limited. Neither ingenious laboratory techniques nor brilliant
computer skills are capable of saving an image without any detail at the boundary areas between
light and shadow.
The diverse exposure options and extensive information provided by modern camera systems would
appear to make external exposure meters superfluous. However, closer examination reveals that this
information is only conditionally meaningful for an evaluation of correct exposure.
Integrated exposure meters are limited.
Modern analog and digital cameras always function in accordance with the reflected light metering
method, i.e. they measure the light reflected by the subject through the lens, and usually provide
several reliable and accurate ways of setting exposure. And thus segmented or matrix metering,
center-weighted metering and spot metering come to grips with many of the exposure problems
encountered in practical photography, but by far not all of them!
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Camera displays are not calibrated.
Visual checking of the exposure setting at a camera display which is not calibrated for brightness and
color is only capable of revealing gross exposure errors, even if the display is well adjusted. Outdoors
in the sunlight, exposure becomes a game of chance. The image frequently has an entirely different
appearance in a calibrated monitor.
Histograms only show the distribution of tonal values throughout the entire image.
The histogram merely depicts the distribution of tonal values throughout the entire image and must
be interpreted depending upon the subject, as well as lighting. The photographer needs lots of
practice and experience to this end. Only in rare cases does the subject to be evaluated fill out the
entire image area, which means that the histogram doesn’t say anything about the evaluation of the
subject or the segment.
Subsequent exposure corrections are greatly limited and time consuming.
Subsequent correction options available at the computer are time consuming, are incapable of
replacing missing detail in highlighted areas and shadows, and represent a direct contradiction to the
dynamic workflow associated with digital photography. Post-processing is always equated with the
removal of information. If a tonal range which is too small is expanded, information gaps always
occur which appear in the histogram as the dreaded “picket fence”.
Handheld Exposure Meter as a Sensible Supplement to an Integrated Exposure Meter
Precise, repeatable exposure plays a significant role, and may not be left to
chance. Exposure meters which are integrated into the camera function in
accordance with the reflected light metering method and only show the correct
exposure value if the subject itself reflects 18% of the incident light (gray
chart). Handheld exposure meters which also use this metering method are
subject to the same limitations, but they offer additional functions as image
composition tools which go well above and beyond the possibilities of
integrated metering systems. These include precise incident light measurement
with spherical or flat diffuser, flash measurement with evaluation of the
incident light ratio, differentiated contrast measurement and mean value
generation, as well as spot metering independent of focal length and
measurement and evaluation in accordance with the zone system.
Better Results with the Incident Light Metering Method
Handheld exposure meters make use of the incident light metering method,
i.e. they measure the light which strikes the subject and calculate a more
precise exposure independent of the subject’s color and reflectivity. This is
especially advantageous for primarily bright or dark subjects. In the case of
exposure meters with flat diffusers, the otherwise spherical acceptance angle
(180°) can be adjusted to a more directional measurement.
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Reflected Light Metering –
Camera
6
Incident Light Metering –
Handheld Exposure Meter
The example white car on white background and black car on black background shows in the pictures above the results of camera internal
reflected light metering and handheld exposure meter incident light metering. The camera interprets in both scenes the brightness as
neutral gray tone (18% reflection) and exposures wrong because the scenes differ extremely from the neutral gray tone.
Measurement of Drop in Luminous Intensity
Within a spatially distributed subject, the intensity of the light decreases by the square of the
distance to the main light source. The closer the main light source is to the subject, the more
noticeable is the drop in luminous intensity. With the incident light metering method, exposure can
be ascertained at the subject’s various depths. The exposure values (EV) can be displayed as a rule at
handheld exposure meters, and the difference between the two measured values results in the
number of f-stops.
Flash Exposure Measurement in the Studio and Outdoors
Handheld exposure meters usually include a flash exposure measurement, i.e. they measure light
from manually operated, compact flash units or studio flash units and ascertain correct exposure
based on measurement results. The ratio between ambient light and flash is frequently displayed as
well. When buying a handheld exposure meter, make sure that this function is supported!
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Adjusting Lighting Contrast in the Studio
In studio photography, lighting contrast is selected depending on the desired visual message and
image impact. It can be defined as the relationships which exist amongst key light, fill-in light, edge
light and background light. The handheld exposure meter based on the incident light metering
method is held at the subject facing the light source to be adjusted, whose power or distance is
varied until the desired value is obtained. As a rule, key light is set as a fixed reference value which
indicates the intensity of the other light sources as deviation from the reference value in f-stops (EV)
with a fixed synchronization speed.
Edge Light
f 11
(+ 1 EV)
Background
Light
f 11
(+ 1 EV)
Fill-in Light
f4
(- 2 EV)
Key Light
f8
reference
Determining Subject Contrast 1
Handheld exposure meters can be used to ascertain subject contrast by means of the reflected light
metering method. While pressing and holding the measurement key, the exposure meter is pointed
at the various brightness values, one after the other, or it scans the entire subject to this end. Some
simpler models then either display the f-stop range (smallest to largest f-stop) or, as is the case with
the GOSSEN DIGISKY, the exposure value difference (EV, f-stops) is directly displayed and the
minimum, mean and maximum values, as well as the associated f-stop / shutter speed combinations,
can also be queried – ideal initial values for HDR photography or for adjustment to the contrast range
of the image recording medium.
Spot Metering with Fixed Acceptance Angle 1
As a rule, spot metering with handheld exposure meters uses a fixed, 1° angle of acceptance and is
capable of measuring small areas very accurately within a complex scene, and it’s also possible to
generate a mean value by taking several measurements. As opposed to this, the measuring range for
spot metering included with modern reflex cameras is indicated as a percentage of the image area
(sensor). The angle of acceptance depends on, and changes along with, the lens’s focal length.
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Pre-Visualization of the Tonal Values with the Zone System 1
With the zone system, final visual results can be viewed for creative planning before the image is
recorded. Use of an 11-stage zone system makes it possible to evaluate deviating brightness within
the subject in consideration of exposure, so that adequate tonal values and detail are present even in
the bright and dark areas of the subject in order to ensure exact reproduction. As a standard feature,
acquired measurement results correspond to the neutral gray tone (18% reflection) in the zone V
tone scale. All of the details which are important for an image recording can then be individually
measured on this basis, and their tonal value can be ascertained.
Medium Gray
18% Reflection
Conclusion
By working with exposure meters in actual practice, photographers become intuitively familiar with
the relationships amongst recording sensitivity, exposure time and f-stop, as well as filter factors and
correction factors, and learn how these different exposure aspects interact to create ideal results.
This gives rise to the following additional advantages:

Correct exposure, even in unusual situations with regard
to subject, lighting and image recording

Deliberate, targeted work instead of tedious
trial-and-error experiments

Reduced effort and time-savings for many tasks,
especially for flash and studio photography

Plannable, measurable and reproducible lighting conditions
assure foreseeable, constant results in the studio

More time for photography, and less time spent on sorting
through exposure variants and post-processing at the computer
In light of all of these positive aspects, there can be only one answer to the provocative question
asked at the beginning of this article:
Working without a handheld exposure meter is possible, but it hardly makes sense!
1)
Depends on the respective model of the handheld exposure meter
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Light in Photography
When we speak of light we refer to the range of wavelengths from 380 to 780 nm from the much
broader spectrum of electromagnetic radiation, which is designated visible radiation (VIS) and to
which the human eye is sensitive.
Electromagnetic Radiation Wavelengths and Frequencies
(source: Wikimedia Commons – Horst Frank – Electromagnetic spectrum c.svg)
This’s also frequently described as the range of optical radiation from 100 nm to 1 mm, which
additionally includes the neighboring, non-visible ranges of ultraviolent and infrared radiation.
Depending on the wavelength, ultraviolet radiation penetrates human skin and can tan us (UV-A),
but is can also cause sunburn and conjunctivitis (UV-B, UV-C). The conversion of atmospheric oxygen
into ozone and germicidal effects (UV-C) are further characteristics. Infrared radiation, which we
perceive and take advantage of as warmth, is less dangerous for people.
Visible light is made up of the primary colors
red green and blue. The receptors in the
human eye can be grouped into three ranges of
sensitivity:
380 to 450 nm – blue
450 to 600 nm – green
600 to 780 nm – red
Mixing the primary colors in equal proportions results in
the color white.
Additive Color Mixing
The colors in our environment are the result of
subtractive color mixing, i.e. the complementary colors
of the primary colors are mixed:
cyan, magenta and yellow.
Mixing the complementary colors in equal proportions
results in the color black.
Subtractive Color Mixing
Arrangement with
Additive Color Mixing
Arrangement with
Subtractive Color Mixing
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2.1 Color Rendering
The color of an object results from partial reflection of the spectrum emitted by the illuminating light
source. If certain ranges are missing from this spectrum, the corresponding color components cannot
be reflected or seen. If intensity is not uniform over the entire spectral range, color components with
greater intensity are amplified, and those with lower intensity are attenuated. If the spectrum of the
incident light is changed, for example through the use of other lamp technologies, the appearance of
the colors of the observed object change as well.
The color rendering properties of a light source are defined by means of the color rendering index.
Light sources for use in photography should have a color rendering index of significantly greater than
90 and a high R9 value for saturated red.
Spectra of Various Light Sources:
Afternoon sunlight, CCT = 5319 K, Ra = 99.2
Light bulb, CCT = 2634 K, Ra = 99.8
Evening sunlight, CCT = 8819 K, Ra = 95.3
Neutral white LED, CCT = 4362 K, Ra = 89.9
Halogen, CCT = 2714 K, Ra = 99.0
TL8 840, CCT = 3781 K, Ra = 82.9
2.2 Color Temperature
The color impression of a light source is defined in terms of color temperature in Kelvin (K). It’s
defined via the temperature of a black object, the so-called Planckian radiator, and the color of the
light emitted by the object at this temperature. When a black object is heated up slowly, it emits
radiation in various colors or wavelengths.
Low temperatures of less than 800 K result initially in infrared light, after which the visible color
range from dark red to red, orange, yellow, white and blue is traversed and finally invisible ultraviolet
light is emitted at above 12,000 K. The temperature at which color balance occurs with the light
source under consideration is the light source’s correlated color temperature (CCT). It can be
measured with a color temperature meter.
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2.2.1
11
Color Temperature Throughout the Day
The color temperature of the light varies greatly during the course of the day and thus influences
mood and color rendering. At sunrise and sundown, warm light immerses the landscape in orange or
reddish hues. As the day progresses the color temperature increases at first, reaching its apex at
midday, and then dropping back off again into the evening.









2.2.2
Sunrise, sundown
Moonlight
Light before 9 a.m.
Light from 9 a.m. to 3 p.m.
Light after 3 p.m.
Sunlight, cloudless sky
Daylight, overcast sky
Cloudy weather
Daylight at the seaside, mountains
2000 to 3000 K
4000 K
4800 K
5400 to 5900 K
4900 K
6500 K
7000 K
8300 K
12,000 to 25,000 K
Color Temperatures of Light Sources
Common lamps have color temperatures ranging from less than 3300 Kelvin (warm white), from
3300 to 5300 Kelvin (neutral white) on up to greater than 5300 Kelvin (daylight white).
Warm White
Neutral White
Daylight White
The precise color temperatures of specific light sources are listed below.













Candle and kerosene lamp
Sodium-vapor lamp (SON-T)
Incandescent household light bulb
Halogen lamp
Standard light type A
Fluorescent lamp, LED (warm white)
Type B Nitraphot photo lamp (500 W)
Type A Nitraphot photo lamp (500 W)
Fluorescent lamp, LED (neutral white)
Xenon lamp (standard)
Electronic flash unit
Xenon lamp (blue)
Fluorescent lamp, LED (daylight white)
1900 to 1950 K
2000 K
2100 to 2900 K
2700 to 3000 K
2856 K
3000 K
3200 K
3400 K
4000 K
4.600 to 4.800 K
5500 to 5600 K
6000 K
6500 K
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2.3 Light Characteristic – Hard and Soft Light
The terms hard and soft light are often encountered in photography when illuminating an object,
although these characteristics do not reflect any actual physical properties of the light. Hard or soft
light is simply the result of the ratio of the light-emitting surface of a source of light to the size of
the object, and is independent of luminous intensity. The following applies in this regard:
The larger the light-emitting surface relative to the object the softer the light.
The smaller the light-emitting surface relative to the object the harder the light.
This ratio can be influenced indirectly by varying the distance of the source of light to the object.
The following applies in this regard:
The greater the distance between the source of light and the object the harder the light.
The smaller the distance between the source of light and the object the softer the light.
Whether light is hard or soft is made apparent by the type of shadows it casts.
Hard light results in dark shadows with abrupt light to shadow fall-off
and clear-cut, sharp edges.
It occurs in the case of sunlight with clear skies, cameras with internal
flash and compact flash units. It’s generated in the studio by means of
snoots, tubes or small standard reflectors. Hard light always occurs
when the light-emitting surface is relatively small in comparison with
the subject.
Soft light results in diffuse shadows with soft, unsharp light to shadow
fall-off.
It occurs in the case of diffuse sunlight with overcast skies, where
diffusers are positioned between the sun and the subject with clear
skies, and inside light tents. When compact or studio flash units are
used, soft light is generated due to indirect flash via white ceilings,
walls, reflective surfaces and reflecting umbrellas, as well as due to
direct flash through diffusers, softboxes or translucent umbrellas. The
reflection or diffusion surface (light-emitting surface) should have a neutral color and be fully
illuminated. Soft light always occurs when the light-emitting surface is relatively large in comparison
with the subject.
Hard or soft light is used as required depending on the situation – it determines the light
effect and underscores the visual message. Hard light is more appropriate in the case of
character portraits of men, whereas beauty photographs of women require soft light. The final
decision is of course made by the photographer.
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2.4 Luminous Intensity – the Inverse-Square Law
The entire luminous flux emitted by a point source distributes itself uniformly in three-dimensional
space over the surface of a sphere which becomes larger in proportion to the square of distance r to
the source. And thus luminous intensity declines at a rate of 1/r². This relationship is known as the
inverse-square law.
Expressed in simplified terms, this has the following significance in the field of photography:
Luminous intensity is reverse proportional to the square of the distance.
or
If distance to the light source is doubled,
luminous intensity is reduced to one fourth of its original value.
Exposure, i.e. the amount of light which strikes the sensor or the film, is controlled by the f-stop
setting in the field of photography. If the f-stop setting is reduced by one step, the amount of light is
cut in half by definition. The series of f-stops normally printed on the lens is:
If we now establish the relationship between the distance of the light source to the subject and the fstop, we obtained the following guiding principle:
Doubling the distance from the light source to the subject
results in a loss of light which is equivalent to two f-stops.
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Within a spatially distributed subject, luminous intensity decreases by the square of the distance to
the main light source. The closer the main light source is to the subject, the more noticeable is the
drop in luminous intensity. Exposure can be ascertained at the subject’s various depths using the
incident light metering method. The exposure value (EV) is displayed as a rule at handheld exposure
meters, and the difference between the two measured values results in the number of f-stops.
If a softbox is positioned at a distance of 1 m from the subject in order to obtain soft
illumination, the photographer has to make sure that the subject doesn’t move around too
much. If he makes just one step backwards, this results in underexposure equivalent to one f-stop as
shown in the example above.
The photographer can also take advantage of this effect. If he positions his light source at a greater
distance from the subject he’ll end up with less luminous intensity and will have to increase the fstop setting, but at the same time, the drop in luminous intensity will be less. This effect is
advantageous for uniform illumination of subjects with varying depth.
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2.5 Influence of Light Shapers
Light shapers not only influence the quality of the light, but rather its quantity as well. And thus each
time the light shaper is changed, it’s essential to reestablish correct exposure. The following example
shows measured f-stop values with constant flash head power at a constant distance.
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2.6 Light Direction
Depending on where the light comes from, various photographic effects can be obtained. The
following graphics provide a brief summary.
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White Balance
When the colors of an image do not appear genuine, the color of the light (color temperature) has
not, as a rule, been correctly matched to the spectral sensitivity of the image recording medium.
Subjectively, the photographer is hardly aware of a color temperature change because the human
eye conducts white balancing automatically by means of chromatic adaptation. It adjusts the
sensitivity of the color-sensitive cells in the retina to this end. A white sheet of paper is perceived as
equally white under artificial light or daylight.
Intentional white balance mismatching can be used as a creative tool in the field of photography. The
use of indoor film or setting white balance at a digital camera to artificial light or cold light results in a
blue color cast in daylight image recordings, which provides architecture photos with an interesting,
cold light mood.
3.1 White Balance in Analog Photography
In analog photography, rough white balancing is conducted initially based on the utilized type of film.
Selection can be made between daylight film which is sensitized for a color temperature of 5500
Kelvin or indoor film for a color temperature of 3200 Kelvin (type A) or 3400 Kelvin (type B). Fine
adjustment of the illumination’s momentary color temperature to the utilized film is accomplished
through the use of finely graduated correction filters which are selected with the help of a color
meter, for example the GOSSEN Colormaster 3F.
Fundamentally, daylight films can also be used for artificial light, but this results in a yellow or orange
color cast. This can be compensated for with blue color correction filters.
Blue color correction filters
3200 K  5500 K
3400 K  5500 K
80A or KB15
80B or KB12
4.0x
3.0x
-2.0 EV
-1.7 EV
Indoor films can also be used in daylight, but this results in a blue color cast. This can be
compensated for with red color correction filters.
Red color correction filters
5500 K  3200 K
5500 K  3400 K
85A or KR15
85B or KR12
2.3x
2.0x
-1.3 EV
-1.0 EV
The filter factors of the individual color correction filters are disadvantageous, and are especially
detrimental when using daylight film in artificial light. Due to the decline of analog photography,
indoor film and color correction filters are only available to a very minimal extent in the meantime.
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3.2 White Balance in Digital Photography
As opposed to analog photography, white balancing has been greatly simplified in digital
photography. The image recorder can be very quickly adapted to changing light situations and the
respectively prevailing color temperature. In the case of RAW files, this step can also be performed
loss-free with the image processing program after recording. If the image is only saved as a JPEG or
TIFF file, it’s advisable to conduct correct white balancing in the camera. Subsequent color
temperature adjustment is difficult and may result in reduced image quality.
3.2.1
Automatic White Balance
Automatic white balance is usually abbreviated AWB and is used as the default setting for practically
all digital cameras. The camera’s software analyzes the recorded image and makes its own decision
regarding color correction. In the simplest of all cases, the software looks for an image area which is
white or nearly white. If no such area is found, it’s assumed that the brightest area of the image is
neutral gray, and this area is used as a reference for correction. White balancing only becomes
problematic and causes a color cast when the brightest area of the image is in color. Unfortunately,
the manufacturers don’t publish detailed descriptions of the calculations used for automatic white
balance.
Generally speaking, automatic white balance functions quite reliably in standard situations but it
frequently fails under difficult lighting conditions and in situations involving mixed light sources,
especially where different types of light occur at the same levels of intensity. The only solution is to
switch over to manual white balance, even if the camera is then no longer able to automatically react
to rapidly changing lighting situations.
3.2.2
Manual White Balance with Presettings
In addition to automatic white balance, digital cameras also offer fixed presettings for the color
temperature of various types of light such as artificial light, fluorescent lamps, flash, daylight, direct
sunlight, overcast sky and shadow.
The preset white balance values can often be fine tuned, thus doing justice to the photographer’s
individual requirements. With some cameras, primarily semiprofessional and professional products,
color temperature can be entered directly in Kelvin or selected from a table.
3.2.3
Manual White Balance with Gray Reference
Manual white balance with the help of a neutral gray or white reference object is highly advisable for
colored light or mixed light. Using a gray card which is suitable as a reference for digital photography
keeps the photographer on the safe side. The frequently referred to sheet of white paper is only
suitable under certain conditions, because paper often contains optical brighteners and thus reflects
a large blue component, which cannot be detected by the eye. Aside from classic gray cards, other
tools are also offered which additionally include black and white, as well as intermediate gradations
or gray step wedges. These make it possible to adjust contrast subsequently in the image processing
program, assuming that the RAW image recording format is used.
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3.2.4
19
Manual White Balance with White Balance Filter
White balance filters laid out as lens covers or lens covers with special diffusers can be used as an
alternative to white balancing with a gray card. The highest quality representative of this species is
the ExpoDisc, which is furnished with a calibration certificate. Not only can white balancing be
performed with this disc – thanks to calibration, it’s also suitable for exposure metering in
accordance with the incident light metering method. When working with these products, one
normally faces the main source of light. If this is not possible or if mixed lighting conditions prevail,
one can also face the subject and use the reflected light for white balancing.
3.2.5
White Balance under Mixed Lighting Conditions
Mixed lighting conditions prevail when several light sources with different color temperatures are
active at the same time. This presents the photographer with two different challenges. On the one
hand, due to chromatic adaptation of the human eye he’s hardly able to detect the mixed light and,
on the other hand, the camera only offers white balance for a single color temperature so that a
color cast cannot be avoided in some image areas. There are various approaches to solving this
problem.
Avoiding Mixed Light
One should always consider whether or not mixed light can be avoided by switching off or replacing
individual light sources. For example, if incident daylight disturbs an artificial light setting and is
unnecessary in order to illuminate the scene, photos can be shot in the evening or the windows can
be blacked out. This is certainly the simplest solution.
Color Temperature Matching
The color temperatures of the individual light sources can be matched to each other through the use
of color filters. The compact flash unit which is pre-matched to daylight and changed to match the
color temperature of light bulbs or fluorescent lamps with the help of included filters is a typical
example. White balance is then performed based on the uniform color temperature.
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Color Matching with Image Processing
Subsequent white balance by means of image processing offers the greatest degree of freedom, but
frequently necessitates the most amount of effort as well. In the simplest of all cases, white
balancing is based on a single color temperature and the color cast for the other color temperature is
partially corrected. A somewhat more complicated procedure involves separate white balancing for
the individual color temperatures, each at a given layer, and partial correction by means of merging
through the use of a layer mask and opacity. Image recordings in the RAW format are a prerequisite
for this after-the-fact procedure.
3.2.6
White Balance and Color Profiling
In the field of product photography, precision color representation is also required in addition to the
right white balance. A color profile, which can be integrated into the image processing program and
used for all of the images of a given series, is created for the respective combination of light, camera
and subject with the help of a color reference table and suitable software.
ColorChecker Passport from x-rite and it’s various possible applications are discussed here as an
example. Various reference cards are provided in a handy plastic case.
White Balance Reference Card
The spectrally neutral white balance target is used for correct white
balancing either in the camera or during post-processing. The userdefined white balance assures a consistent white point throughout a
series of images and saves considerable amounts of time as opposed
to subsequent correction of individual images.
Classic Reference Card
The classic reference card has 24 color fields, each of which
corresponds to a color which occurs in nature and the light reflected
by these colors. These include, for example, sky-blue, skin colors and
leaf green.
The card, which is photographed along with the subject, can be used
either as a visual color reference or as a basis for the creation of
DNG profiles with the included Passport software. In this way, the
camera’s reaction to various lighting conditions can be precisely acquired and automatically applied
to all of the images of a given series, thus making it possible – as opposed to manual correction – to
obtain accurate, reproducible image results.
Optimization Reference Card
The optimization reference card includes 4 lines with color fields
which have been specially developed for uncomplicated postprocessing of photos with the pipette.
The two middle lines include warming or cooling fields, by means of
which skin colors in portraits can be made warmer, or blue and gray
tones in landscape images can be made more intensive.
The bottom line includes HSL fields for hue, saturation and lightness with eight spectrum fields, by
means of which the color fidelity of all of the colors of the spectrum can be assured.
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The bottom line includes fields which are used as a visual reference for the correction of light and
shadow details. The image processing program is frequently capable of restoring overexposed
highlights and underexposed shadows, if the corresponding details are still included in the RAW file.
Passport Software
Used together with the classic reference target, ColorChecker Passport software for camera
calibration and the plugin for Adobe® Photoshop® Lightroom® permit quick and uncomplicated
creation of DNG profiles for Adobe® imaging programs such as Photoshop®, Photoshop® Lightroom®,
Photoshop® Elements, Camera Raw (ACR) and Adobe® Bridge.
Regardless of camera or lens make and model, ColorChecker Passport provides the user with a basis
for color reference and complete control over the colors. This includes:





Extended functionality for calibration and color control when using the RAW image format
Accurate color reference as a basis for creative post-processing
Elimination of color differences resulting from different cameras and lenses
Adjustment to mixed lighting
Color matching of various scenes for a uniform look
3.3 White Balance in the Digital Camera
The following overview depicts white balancing options in the digital camera and provides a
recommendation for studio photography.
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22
Fundamentals of Exposure
A subject which is illuminated by ambient light is a basic prerequisite for any image recording. Only in
the studio does one have full control over ambient light. In the case of landscape and architecture
photography the outdoor lighting situation depends on the time of day and weather conditions. If
lighting conditions are unfavorable, image recording has to be postponed to a more suitable point in
time. Ambient light can hardly be influenced by the photographer, or only with great effort.
Ideally, the term exposure means that exactly the right amount of light acts upon a light-sensitive
medium in order to obtain an optimum image which corresponds to our visual impression. It doesn’t
matter whether we’re working with analog film or digital camera sensors. The amount of light is
controlled by the f-stop, i.e. the size of the lens aperture, and duration, i.e. shutter speed. The
sensitivity of the image recording medium is specified by the ISO sensitivity rating of the film or
sensor.
4.1 The Exposure Triangle
Low –
Minimal Sensitivity,
Minimal Snow
High –
High Sensitivity,
Much Snow
Fast –
Frozen Motion,
Minimal Blurriness
Large –
Minimal Depth of Focus
Small –
High Depth of Focus
Shutter Speed
Slow –
Dynamic Images,
High Risk of Camera Shake
All three factors – f-stop, shutter speed and sensitivity – depend on each other.
If one value is changed, at least one of the other two values has to be adjusted in order to obtain an
identically exposed image.
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4.2 F-Stop
The lens’s f-stop controls the amount of light which acts upon the
film or the sensor via the aperture. The diameter of the aperture is
defined as focal length f / f-stop. In normal daily use only the f-stop
is used, i.e. the denominator, which means that a small f-stop
corresponds to a large aperture.
The series of f-stops itself is laid out such that the amount of light is
either cut in half or doubled from one f-stop to the next, i.e. cut in
half from f-stop 4 to f-stop 5.6 and doubled from 4 to 2.8.
This relationship is the result of the aperture. The amount of light is
determined by circle area A = π * r², i.e. doubling the surface area of the circle results in twice as
much light. The fact that the diameter of the aperture is equal to focal length f / f-stop results in a
factor of √2 ≈ 1.4141 for gradation.
Most cameras and lenses make adjustment possible in ½ or ⅓ stops, thus permitting precision
exposure adjustment.
Small f-stop number = large aperture and minimal depth of focus.
Large f-stop number = small aperture and large depth of focus.
High-speed lenses have a large aperture which can be used for cropping objects or to
achieve short exposure times. The larger the aperture the smaller the depth of focus.
Roughly ⅓ of the depth of focus is in front of the object and ⅔ are behind it. A lens delivers maximum
depth of focus when it’s stopped down roughly 2 to 3 f-numbers. If it’s stopped down even further,
light diffraction at the aperture blades leads to reduced depth of focus.
4.3 Shutter Speed
The camera’s shutter speed controls the amount of time during
which light acts upon the film or the sensor. Shutter speed is usually
specified in fractions of a second.
The series of shutter speeds itself is laid out such that duration, and
thus the amount of light as well, is either cut in half or doubled
from one shutter speed to the next, i.e. cut in half from 1/125 s to
1/250 s and doubled from 1/125 s to 1/60 s.
Most cameras make adjustment possible in ½ or ⅓ shutter speeds,
thus permitting precision exposure adjustment.
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Short exposure times are required in order to avoid blurring in the case of moving subjects
or camera shake in the case of greater focal lengths. A long exposure time can also be used
as a creative tool in order to make moving subjects such as flowing water or the ocean appear out of
focus.
4.4 Shutter Speed / F-Stop Combinations
The amount of light which strikes the film or sensor results from the combination of f-stop and
shutter speed. The larger the aperture the shorter the exposure time has to be for a correctly
exposed image. Conversely, the smaller the aperture the longer the exposure time has to be where
luminous intensity remains unchanged.
And thus there are various possible shutter speed / f-stop combinations for correct exposure where
luminous intensity remains constant. For example, combining f-stop 2.8 with a shutter speed of
1/2000 s yields the same result as combining f-stop 4 with a shutter speed of 1/1000 s or 5.6 with
1/500 s.
4.5 ISO Sensitivity
How much light has to reach the film or the sensor for correct
exposure depends on its sensitivity, which is usually specified in ISO.
Doubling the ISO value results in twice the sensitivity and thus
corresponds to one exposure value.
In analog photography, sensitivity is dictated by the utilized film.
Film with a low ISO value has a fine grain structure and thus high
resolving power. Film with a high ISO value requires a coarser
grained structure and thus demonstrates a given degree of
graininess.
In digital photography, the sensor’s sensitivity to light is also specified as an ISO value, and every
sensor has a nominal sensitivity – usually ISO 100. Greater levels of sensitivity can be achieved by
means of signal boosting with the camera’s electronics and result in more snow. Due to the fact that
the ISO value can be set individually for each image recording, digital photography offers a further
element for controlling exposure in addition to shutter speed and f-stop.
Best possible image quality is obtained when nominal sensor sensitivity is used. As the ISO
value rises, snow increases and image quality declines. As the size of the image sensor
increases, and along with it the size of the light-sensitive surface of the individual pixels,
more and more light strikes the diode and the sensor becomes more sensitive. Special care is
required in the case of automatic ISO settings because the ISO value, and thus image quality, vary
from one image recording to the next
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25
How does an Exposure Meter Work?
External, handheld exposure meters, as well as exposure meters integrated into the camera, always
work in accordance with the photoelectric principle. A light-sensitive sensor transforms the
prevailing amount of light into an electrical signal, which is in turn converted into a measured value
by the electronic circuitry and the device software.
5.1 Standardization to 18% Gray
All exposure meters, whether external or integrated into the camera, are calibrated to arrive at
exposure values which result in images with medium brightness. The gray cards offered by various
manufacturers reflect 18% of the image recording light and serve as a reference value for medium
gray, as well as for balancing the exposure meter.
5.2 Exposure Value (EV)
Fundamentally, all exposure meters first of all measure the exposure value, from which they
determine the f-stop / shutter speed combination required for the photograph. Any given exposure
value corresponds to several shutter speed / f-stop combinations, any one of which can be used as
desired in order to expose the film or the sensor to the same amount of light.
External light meters usually display the exposure value (EV) in addition to the f-stop / shutter speed
combination, thus permitting simple calculation with exposure values, as well as shutter speeds and
f-stops as required for contrast measurements, for example. On the other hand, exposure meters
integrated into the camera only display shutter speed / f-stop combinations.
The relationship between exposure values and shutter speed / f-stop combinations is shown in the
table below for ISO 100/21°. Exposure value 0 is defined such that an exposure time of 1 second
results from the settings ISO 100/21° and f-stop 1.0. The exposure value increases logarithmically –
doubling illumination intensity increases the exposure value by 1.
EV
2s
1s
1/2 s
1/4 s
1/8 s
1/15 s
1/30 s
1/60 s
1/125 s
1/250 s
1/500 s
1/1000 s
1/2000 s
f/32
9
10
11
12
13
14
15
16
17
18
19
20
21
f/22
8
9
10
11
12
13
14
15
16
17
18
19
20
f/16
7
8
9
10
11
12
13
14
15
16
17
18
19
f/11
6
7
8
9
10
11
12
13
14
15
16
17
18
f/8
5
6
7
8
9
10
11
12
13
14
15
16
17
f/5.6
4
5
6
7
8
9
10
11
12
13
14
15
16
f/4
3
4
5
6
7
8
9
10
11
12
13
14
15
f/2.8
2
3
4
5
6
7
8
9
10
11
12
13
14
f/2
1
2
3
4
5
6
7
8
9
10
11
12
13
f/1.4
0
1
2
3
4
5
6
7
8
9
10
11
12
f/1
-1
0
1
2
3
4
5
6
7
8
9
10
11
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26
Measuring Methods
Fundamentally, cameras determine exposure values by means of reflected light measurement, i.e. by
measuring the light which is reflected by the subject. Depending on the application and the subject,
diverse measuring methods can be selected by means of which the various areas of the image are
weighted differently in order to obtain best possible measurement results. External exposure meters
are preferred for incident light measurement and flash exposure metering. They’re also capable of
reflected light measurement with specific characteristics. The precise exposure parameters for a
single image, or for constant exposure of a series of images, are dictated by the selected measuring
method,
6.1 Reflected Light Measurement
Where reflected light measurement is concerned, the exposure meter acquires light reflected
from the subject to the camera at the photographer’s position. This value, based on all of the
various reflective objects within the image, is used as a tonal value for which required
exposure is calculated. Tonal range, color, contrast, background brightness, surface structure
and reflectivity of the objects influence the measurement results, although they’re not taken
into consideration in evaluating the motif.
Monochrome subjects are reproduced in neutral gray with this measuring method. A bright
subject reflects more light, and is thus represented as darker. A dark subject reflects less light,
and is thus represented as brighter. In other words, if a white and a black car are photographed, both
images will depict the same gray car.
Reflected light measurement of a gray chart in close proximity to the subject delivers more precise
results, because the gray chart reflects exactly the same light component to which the exposure
meter is calibrated. However, this measurement is complicated and in many case impractical.
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27
Average Metering
Average metering takes the entire surface of the image into consideration – the individual areas of
the image are not weighted at all. Each of the subject’s details makes a contribution to the
magnitude of the measurement result depending on its brightness. Due to the considerable
inaccuracy of this measuring method, it often results in incorrect exposure and is rarely used.
6.1.2
Center-Weighted Average Metering
Center-weighted average metering is the standard measuring method for numerous reflex
cameras and is used whenever the main subject is at the middle of the image and isn’t too
small, and where only minimal contrast differences prevail. It takes the overall surface of
the image into consideration, but as opposed to average metering, the individual image areas are
weighted differently. The middle of the image is more significant for exposure, and significance
dwindles towards the outside edges. Areas outside of the image circle have nearly no influence at all.
This error-tolerant measuring method is still used frequently today, because incorrect exposure only
occurs in the case of just a few subjects, is foreseeable and can be easily corrected by an experienced
photographer.
6.1.3
Spot Metering
Spot metering is frequently integrated into modern reflex cameras and is used wherever a
small subject area needs to be measured without weighting, or considerable contrast
differences prevail. The measuring point is usually in close proximity to the focus area or at
the middle of the image, and the measuring range is frequently specified as a percentage of the
surface of the image (sensor). The angle of acceptance depends on, and changes along with, the
lens’s focal length. External spot meters have a fixed, 1° angle of acceptance and are capable of
measuring small areas very accurately within a complex scene, and it’s also possible to conduct
multi-spot metering, i.e. to generate a mean value by taking several measurements.
Spot metering is used when unreliable values are obtained from other reflected light measuring
methods, or where incident light measurement is not possible. As a rule, this involves scenes with
objects at a great distance, backlighting situations, nighttime image recording, extreme differences in
brightness, reflective surfaces or a moving main subject. Special care is required where spot metering
is used, because although it’s capable of measuring specific parts of the subject in a targeted fashion
and thus permits precision work, it can also quickly result in incorrect exposure if the reading is taken
at the wrong place.
6.1.4
Selective Metering
Selective metering is exceptionally well suited for taking readings at subject details which are
important for the image and are not too small. Despite the small segment of roughly 5 to 10%, which
is nevertheless larger than with spot metering which amounts to 1 to 5%, the measured values are
weighted so that error tolerance is somewhat higher than with spot metering. The transition from
spot metering to selective metering is fluid.
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28
Multi-Segment Metering, Matrix Metering
Multi-segment metering, also known as matrix metering, is today’s standard measuring method for
modern cameras. It delivers very good results and is first choice for snapshots and action
photography.
Calculation models, number and weighting of the segments, as well as the influence of lens
specifications such as focal length and focus distance, have developed depending upon the
performance level of the camera’s electronics. Modern cameras also take color distribution into
consideration, or conduct subject detection, both of which influence metering results. Due to a lack
of standardization, multi-segment metering varies from one manufacturer to the next, as well as
from one camera model to another.
Despite the most up-to-date calculation algorithms, or perhaps precisely due to them, multi-segment
metering may result in incorrect exposures which are not however comprehensible and are easy to
correct. This can be remedied by means of manual metering with alternative methods. Manual
metering is frequently more time-consuming than automatic metering, but in many cases it produces
significantly better results.
6.1.6
2-Point Metering
Professional photographers make use of the 2-point metering method. First of all, one chooses the
brightest and darkest point of the subject which will still demonstrate detail, assuming that the
contrast of the subject doesn’t exceed the camera’s dynamic range. The f-stop values are determined
for both of these points with a fixed exposure time. The f-stop which is at the middle of both
measured values is selected for image recording. It must be assured that not the arithmetic mean
value between the f-stop numbers is selected, but rather the mean value in the logarithmic f-stop
series.
6.1.7
Substitution Measurement with Gray Card
The uncertainty factor associated with reflected light measurement is due to the assumption that the
entire object reflects 18% of the incident light. Better results can be obtained if we conduct metering
with a substitute object which fulfills these requirements. A gray card with 18% reflectivity is used for
this purpose.
In the case of three-dimensional subjects, the gray card is
positioned perpendicular to the bisector between the main light
source and the camera’s axis within the motif, and metering is
conducted with the exposure meter at a right angle to the card.
The surface of the gray card must not reflect any glare and must
not be shaded by any objects.
Due to the fact that in the case of diffuse illumination no definite
light direction can be determined, the gray card is held such that
it directly faces the camera. In the case of flat artwork, the gray
card is always positioned parallel to the plane of the artwork
because the brightness of flat artwork is influenced by the exposure angle.
When metering is performed with the camera, it must be assured that the gray card entirely fills out
the viewfinder. This is accomplished by temporarily shortening the recording distance, using a
telephoto lens, zooming in or alternatively by means of spot metering. If a handheld exposure meter
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is used, the gray card must fill out the angle of acceptance. This is accomplished by means of a short
distance to the gray card or alternative use of a snoot.
If the subject is further away or not easily accessible, metering can be performed alternatively at the
camera’s location, assuming that similar light conditions prevail here.
The use of a handheld exposure meter with incident light measurement is much simpler
than this somewhat complex procedure.
6.1.8
Reflected Light Metering Methods of Cameras
The following table compares the reflected light metering methods of cameras, their advantages and
disadvantages, and their respective areas of use.
6.2 Incident Light Measurement
The incident light measuring method is only possible with external exposure meters
and is frequently used by professional photographers. As opposed to reflected light
measurement, the light striking the subject is measured instead of the light reflected
by the subject. A semispherical diffuser head is attached in front of the sensor to this
end, which covers a spherical angle of acceptance of 180° and demonstrates 18%
transparency. In this way, the exposure values are derived directly from the incident
light regardless of the color, brightness and reflectivity of the subject.
Metering is performed in front of the subject in the direction of the camera, or in
the case of three-dimensional subjects with the main source of flight in front of the subject, towards
the bisector between the camera and the main source of light. In the case of outdoor image
recordings, metering can be conducted alternatively at the camera’s location assuming that
comparable light conditions prevail here.
Some exposure meters make it possible to replace the spherical diffuser with a flat one, or to switch
back and forth, thus providing for a more directed characteristic. For example, this is used for
metering several sources of light in the studio and adjusting lighting conditions.
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The decisive advantage of the incident light measuring method is the fact that bright objects appear
bright in the image and dark objects appear dark.
Reflected Light Measurement, Camera
Incident Light Measurement, Handheld Meter
The example of a white car against a white background and a black car against a black background in
the images shown above demonstrates the results of reflected light measurement with the camera
and incident light measurement with a handheld meter. For both subjects, the camera sees image
brightness as medium gray (18%) and exposes the images incorrectly because the brightness of the
subjects deviates significantly from medium gray.
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31
Flash Exposure Metering
Where several flash units or a combination of ambient light and flash is used, exposure meters which
are integrated into the camera are inadequate, because all of the sources of light which illuminate
the scene have to be individually evaluated and added up. External exposure meters are capable of
measuring individual flashes, calculating multiple flashes in the event of insufficient flash power and
analyzing the ratio of flash to ambient light – even where several sources of light interact with each
other.
A second, and much greater benefit, results from using the meter to adjust the lighting conditions of
the individual sources of light to each other. This makes it possible to use flash as a creative means,
and to set up any desired lighting mood quickly and reproducibly with any flash system and light
shaper. Evaluation of the ambient light ratio makes it possible to adjust fill-in flash for outdoor use,
or as the main source of light. Tedious experiments with the power settings of individual flash units
are thus a thing of the past.
7.1 Adjusting Studio Lighting – Lighting Contrast
One often works with several sources of light in the studio, of which at least one is main light. As a
rule, the other sources of light are only used to brighten up the shadows on the subject, as special
effect light for the contour or the hair of the model or to emphasize an object’s structure, surface or
material, or to define a brightness curve for the background.
Lighting contrast is selected depending on the desired visual message and image impact. It can be
defined as the relationship which exist amongst main light, fill light, special effect light and
background light. The handheld exposure meter based on the incident light metering method is held
up at the subject facing the light source to be adjusted, whose power or distance is varied until the
desired value is obtained. As a rule, main light is set as a fixed reference value which indicates the
intensity of the other light sources as deviation from the reference value in f-stops (EV) with a fixed
synchronization speed.
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The following graphic shows the adjustment of lighting contrast based on the example of a lighting
arrangement and provides additional information for camera settings.
F-Stop 11
(+ 1 EV)
F-Stop 4
(- 2 EV)
F-Stop 11
(+ 1 EV)
F-Stop 8
F-Stop 8,
Referenc
e
The following graphic shows examples of the results of the exposure settings and their variants.
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7.2 Triggering the Flash Unit with the Camera
Triggering of the flash unit must be synchronized with the camera’s shutter release button so that
the film or the sensor is exposed to flash with fully open shutter. The shortest synchronizing time for
common cameras is usually somewhere between 1/125 s and 1/250 s. The exact value for the
respective camera model can be found in the operating instructions.
Triggering is simplest with the help of a synchronizing cable which is
connected between the synchronizing socket at the camera or a flash shoe
adapter and the flash unit to be triggered. However, use of this method is
restricted because it limits the photographer’s freedom of movement and
may lead to damage of the equipment.
Wireless flash triggering kits are the most elegant, universal and safest
solution for triggering flash units. A kit usually consists of a transmitter
which is mounted to the camera and a receiver which is plugged into the
synchronizing socket at the studio flash unit. The other studio flash units
can either be triggered by the normally integrated photocell, or more
elaborately equipped with a separate wireless receiver. The second
method is preferable for outdoor applications, because optical triggering
doesn’t work in this case. Some flash manufacturers integrate wireless receivers into their flash
heads by means of which power control and subdivision into groups (main light, fill light, affect light
and background light) is also possible for separate as well as common triggering.
7.3 Triggering and Metering with the Exposure Meter
The simplest type of metering is conducted in the exposure meter’s non-cord mode. Metering is
started in the flash mode by pressing the metering key and the flash unit is triggered by a wireless
transmitter – either as a separate unit or attached to the camera. The exposure meter detects the
light pulse, measures the value and displays the result. The desired sensitivity and synchronizing time
must be set at the exposure meter.
The second option involves connecting the exposure meter to the system via a synchronizing cable.
When the metering key is pressed, the flash unit is triggered automatically and the measured value is
displayed. The exposure meter’s synchronizing socket can also be connected to a wireless triggering
device instead of the synchronizing cable. In this case, the flash unit is triggered by means of a radio
signal when the metering key is pressed. Flash head power can also be controlled by the wireless
triggering device, if this function is supported.
The most elegant solution is an exposure meter with already integrated wireless
transmitter, for example the DIGISKY from GOSSEN. Triggering the flash unit, metering
and adjusting flash power are all possible with a single device in this case. There’s no
need to actually go to the flash head in order to adjust power. As a prerequisite, the
exposure meter has to support the flash unit’s wireless protocol or the flash unit has to
be equipped with a wireless receiver which is supported by the exposure meter. The
DIGISKY currently supports flash units from Elinchrom and Broncolor, as well as their
wireless triggering kits, and wireless triggering kits from Phottix and the Calumet Pro
series.
7.4 Combining Flash and Continuous Light
Flash is frequently used for fill-in together with continuous light in order to brighten up shadows or
to obtain more brilliance and color saturation with diffuse illumination. TTL flash control included
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with modern cameras supports this application for matching system flash units, but the results are
usually incomprehensible to the user and can’t be significantly influenced. The resulting images often
appear over-flashed or unnatural.
The user has full control when the process is manually controlled. Determination of correct exposure
and the flash-to-daylight ratio is very simple. Background exposure is determined first and entered to
the camera. It must be assured that the selected exposure time is not shorter than flash sync time.
The second step involves the measurement of flash from the surface of the subject which needs to
brightened using the flash exposure meter in the incident light mode. Flash unit power or distance is
adjusted such that the measured f-stop is roughly 1 to 2 steps (EV) below the value set at the
camera.
If the specified f-stop needs to be opened up further in order to achieve the desired
image impact, either a lower sensitivity setting can be selected at the camera or a
neutral-density filter can be used to weaken main light. This effect influences fill-in flash
to just as great an extent, which has to be taken into account during measurement by entering a
correction value at the exposure meter.
External exposure meters frequently provide us with information
concerning the flash or continuous light component. For example,
GOSSEN’s SIXTOMAT F2 and DIGIPRO F2 exposure meters indicate f-stop 16
and shutter speed 1/60 s at the digital display for the combination of flash
and continuous light. This value of 16 appears as a blinking marker in the
analog f-stop display, and f-stop 8 appears additionally as an continuous, active marker for the
continuous light component.
The flash component is displayed at the DIGISKY for GOSSEN as a percentage,
for example. The relationship between flash and continuous light can be
influenced by changing synchronization speed. This is interesting for brightening up
with flash, or when continuous light is not desired. If the flash unit is powerful
enough, images with a dark background can also be recorded in daylight. In order
to adjust synchronization speed, it may be necessary to work with a neutral-density
filter which correspondingly weakens the daylight component.
When flash is used, the continuous light component is controlled by synchronizing speed.
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35
The Zone System
The zone system was developed by Ansel Adams in order to obtain ideally printable negatives from
the analog photography process with the film materials available at that time, which demonstrated a
limited contrast range, by controlling developing time. During the course of time the zone system
has lost in significance for the development of analog film materials because, on the one hand,
negatives were no longer developed individually but rather in rolls and, on the other hand, because
modern film and printing paper can handle a larger contrast range.
In the age of digital photography, the contrast range can be selected and final visual
results can be viewed for creative planning before the image is recorded with the
help of the zone system.
Use of an 11-stage zone system makes it possible to evaluate deviating brightness
within the subject in consideration of exposure, so that adequate tonal values and
detail are present even in the bright and dark areas of the subject in order to ensure
exact reproduction.
As a standard feature, acquired measurement results correspond to the neutral
gray tone (18% reflection) in the zone V tone scale. All of the details which are
important for an image recording can then be individually measured on this basis
and allocated to the respective zone.
Definitions According to Ansel Adams
Shadow zones
I
Nearly black
Blackening without detail, noticeable differences to zone 0
II
Gray-black
Insinuated detail, very dark shadows, black
clothing, black textiles, dark pine forest in shadows
III
Very dark gray
Shadows with detail, forest in sunlight, moist earth
Medium gray tones
IV
Dark gray
Dark foliage and grass, stone, woodwork, shadow zones in portraits,
sky with red filter
V
Neutral gray or
medium gray
Gray values with 18% reflection, gray card, average
detail in wood, stone, dark skin colors
VI
Light gray
Light skin color, bright blue sky, light colored stone, shadows on
snow in sunlight
Bright zones
VII
Very light gray
Very light skin colors, bright textiles, snow with light from the side
VIII
White with detail
Brightest parts of the subject which still show detail, snow with
detail, highlights on skin
IX
White
Polished surfaces without detail, snow with sunlight from the front
Medium Gray
18% Reflection
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Exposure Metering Compendium
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36
The Histogram
The histogram depicts the static distribution of an image’s tonal values. Relative to brightness, the
camera arranges all of the pixels along a horizontal scale from 0 (black) to 255 (white). The height of
the individual line indicates the number of pixels of identical brightness. The fine lines which are very
close to each other may result in a gentle curve, a jagged mountain, a picket fence or a combination
of any two or all three.
All of the following three images are correctly exposed, underneath which the associated histograms
are included.
It’s apparent that a histogram provides information regarding the distribution of tonal values within
the image, but does not offer any indication of lighting conditions, the ambient light to flash ratio or
even whether or not the image is correctly exposed.
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10 Controlling Contrast
Exposure metering only makes sense if contrast is also taken into consideration, which is decisive for
rendering of the tonal values.
Object contrast depends entirely on the material of the subject to be photographed and is
independent of lighting. It indicates the ratio between the point with the most and the point with the
least reflectivity.
Lighting contrast is the maximum difference between illumination intensity measured at different
sides of the subject.
Subject contrast is the combination of object contrast and lighting contrast. It designates the ratio
between the brightest and the darkest portions of the subject which are important to the image. This
is ascertained by means of close-up or spot metering and is specified in exposure values or f-stop
steps. One exposure value is equal to one full f-stop.
If subject contrast exceeds the dynamic range of the recording medium, i.e. the total number of
brightness levels which the medium is capable of reproducing, the bright or dark parts of the subject
appear showing no detail and cannot be improved by means of post-processing.
Overview of Dynamic Ranges of Various Recording and Reproduction Media
Recording Medium
Digital reflex camera
Dynamic Range [EV / f-stops]
Black-and-white negative film
Color negative film
Color transparency film (slide)
10
9
8.5 … 9
7.5
11 … 13
8 … 10
6…8
Reproduction Medium
Dynamic Range [EV / f-stops]
Standard monitor
Digital projector
Slide projector
Photo paper
Photo printer
8 … 10
9 … 12
8
4…6
5…8
Digital compact camera
100 ASA
400 ASA
100 ASA
400 ASA
Fundamentally, differentiation can be made amongst three situations. Subject contrast is less than,
equal to or greater than the dynamic range of the recording medium.
If subject contrast is less than the dynamic range of the recording medium, elbowroom is available in
the case of correct exposure. If the average value between the brightest and darkest points is used
for exposure metering, average brightness can be shifted in both directions without losing detail.
If subject contrast is equal to the dynamic range of the recording medium, precise exposure is
required because any shifting inevitably leads to a loss of detail.
If subject contrast is greater than the dynamic range of the recording medium, the range of tonal
values can no longer be imaged. Correct exposure is no longer possible. If the average value between
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Exposure Metering Compendium
38
the brightest and darkest points were used for exposure metering, detail would be lost in the dark as
well as the bright areas. Depending on subject and image impact, the photographer would then have
to decide which tonal values are most important and adjust exposure if necessary.
Use of the Available Dynamic Range – Optimized Workflow
Metrological analysis of both illumination and the subject make it possible for the photographer to
take ideal advantage of the available dynamics range of the recording sensor and the output media,
right from the very start. Adaptation by means of tedious post-processing is unnecessary, and the
fast-paced workflow associated with digital photography remains unimpeded. Suitable measuring
functions include:
Contrast measurement:
Subject contrast from the brightest to the darkest areas of the subject
with detail
Averaging:
Mean value based on measured values from important areas of the
subject
Zone measurement:
Assignment of brightness values to defined gray values
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Exposure Metering Compendium
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11 Recommended Reading
Books
Das Blitz-Kochbuch
Kreative Blitzfotografie in der Praxis
Andreas Jorns
dpunkt Verlag, ISBN 978-3-89864-773-1, www.dpunkt.de
Belichtungsmessung
korrekt messen richtig belichten
Adrian Bircher
Verlag Photographie, ISBN 3-933131-59-6
Fotografieren im Studio
Das umfassende Handbuch
Michael Papendieck, Galileo Design, ISBN 978-3-83621-984-6
Portraits fotografieren im Studio
Schritt für Schritt erklärt: perfektes Licht im Studio
Stephanie Eckgold, Frank Eckgold, Galileo Design, ISBN 978-3-83621-649-4
Free Leaflets
Hensel Lichtformervergleich
Hensel Light Guide
www.hensel.eu/lichtformervergleich/
19 February 2018
2
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