Every time we take a
photograph, it is necessary to use accurate exposure settings, regardless if we
use film or digital cameras. Automatic
exposure control has advanced to the point that in most cases we can rely on
our camera equipment to come up with the correct camera settings. However, there will be times when this won’t
work, when the light meters in our cameras will be fooled. Take a bright, sunlit winter scene, for instance. The snow will reflect a huge amount of light
which will fool our built in light meters into registering a larger amount of
light than what is actually available.
The result will be an underexposed picture with the snow being rather
dingy. Not at all what the scene looked
like.
In cases like this, many
people will set their cameras to automatically overexpose by a stop or two, but
that is nothing more than guess work.
Ideally, a handheld light meter is the most accurate instrument to
determine the correct exposure setting.
Since the advent of the
early selenium cell light meters in the 30s, light meters have come a long
way. Built-in, automatic exposure
control has made exposure settings so effortless that a lot of camera users
hardly give it a thought anymore. On the
other hand, especially in professional applications, full manual control over
exposure settings is often an absolute must.
A portrait for instance might call for a white background. Obviously, a white background material, like
seamless paper, is the correct choice here.
Yet, just because we use a material which we consider white, this does
not necessarily turn into a white background in a photograph. As a matter of fact, given the right control,
a photograph taken of a subject against a white background can actually result
in a photograph which shows a very dark or even black background, just as a
black background can be rendered white in a photograph. All that is necessary is a good understanding
of exposure and a good hand-held light meter.
Most hand-held light
meters are basically designed as incident light meters, yet for full control
over our exposure settings a reflective light meter is absolutely necessary
also. Let’s look at the
differences: A reflective light meter,
like all of the light meters built into our cameras, reads the intensity of the
light which is reflected off the subject.
An incident light meter on the other hand will read the intensity of the
light which illuminates the subject. A
closer look at both types will reveal their inherent differences.
Gossen Sixtomat F2
The meter is in the incident
reading position.
To switch to a reflected
reading, all that is necessary
is to slide the incident
sphere off to the side.
Sekonic L-478D
The meter as shown is for
incident readings.
In order to switch to
reflective reading,
a separate reflective reading
attachment needs
to be purchased. To take a
reflected reading,
it is necessary to remove
the incident sphere
and replace it with the
reflective reading attachment
If we take a reflective
light meter and aim it at a subject of average brightness, it will give an
accurate reading. For easier
understanding, let’s aim the light meter at an area which is painted an average
gray. Such a surface will reflect an
average amount of the light which illuminates it and the meter will react
accordingly, giving a certain exposure setting.
Without change in illumination, if the gray area is replaced by a pure
white one, what will happen? The white
surface obviously will reflect a lot more light which the light meter will
register. Replacing that area with a
black one will result in just the opposite.
Without any change in relative brightness, our meter has now come up
with three distinctively different exposure settings.
Reflective light meters
are all calibrated to register (or assume) an average level of reflectance, as
with the gray surface. Subsequently, the
exposure reading obtained from the gray surface is the correct one. The white surface will actually fool the
meter into registering a higher light intensity, just as the black one will
result in registering a lower light intensity.
Both of those exposure settings will be wrong. The end result is actually that the meter
will render exposure settings which make all three surfaces in the photograph
grey. This is the very reason why
photographs of a snow scene will usually be underexposed, while photographs at
dusk or at night often come out much lighter than the actual scene.
This is where an incident
light meter has tremendous advantages.
It only registers the relative brightness of illumination. The resulting exposure settings will make an
object of average brightness average in the photograph also. Subsequently, a lighter surface will be
lighter in the photograph just as a darker one will show up darker.
So it may seem that for
accurate camera settings an incident light meter is the way to go. In most situations this actually is indeed
the case. But what about a white
background? The exposure setting we
choose has to be such that not only the subject is exposed properly, but also
the background, which in our example is to be white.
A three stop overexposure
will generally result in white, just as a four stop underexposure will result
in black. This is easily verified by
taking an evenly illuminated white back ground and taking a reflective
reading. We then open the lens by three
stops and take an exposure. Then
subsequent exposures are taken in 1/3 stop increments until a four stop
underexposure has been reached. The
results will then show the various shades of gray (white and black are also
considered shades of gray here) which can be achieved with various degrees of
over and under exposure. Please note
that these are average settings. Digital
sensors vary in their response to over and underexposure. However, a simple test like the one above
will easily show the amount of overexposure and underexposure necessary to
render white or black without detail.
For example, if for a
white background it is necessary to see if it is three stops overexposed, we
must do the following:
We determine the correct
exposure for the subject with the light meter in the incident mode. This will be very accurate and therefore
establish the actual camera settings.
These settings also need to overexpose the background by three stops in
order to render it white. To check this,
all we need to do is switch the meter to the reflective mode. Now the meter will register the amount of
light which is actually reflected by the background. If this indeed shows an overexposure of three
stops, the background will be white, as would a four or 5 stop
overexposure. But that is not advisable
at all since otherwise the background will reflect such a strong amount of
light that it very likely will result in flare or loss of detail at the edges
of the subject. If the reflective
reading of the background registers less than a three stop overexposure, it is
ultimately a simple interpretation of what the background will look like. A two stop overexposure for instance would
render a very light gray background; a one stop overexposure would still render
a noticeably lighter grey. The same
exposure as the one for the subject would render an average or neutral grey,
while underexposure would render progressively darker shades of grey until the
background is rendered black.
For example: The basic exposure for the subject is 1/60
sec @ f/5.6. For the background to be
three stops over, the meter would have to read 1/60 @ f/16. If we were to expose at f/16, the background
would be medium gray, but since the actual camera setting for the subject calls
for f/5.6, that is indeed a three stop overexposure compared to f/16. Does it matter if the background material is
actually white? No it does not! Regardless of color or brightness, if the
background is illuminated such that it registers a three stop overexposure, it
will be white. On the other hand, if the
overexposure is less than three stops, the background will show various degrees
of light grey, red, green or whatever other color the background may be, but
with an underexposure of four stops, all will be black.
The above photograph is a
good example of predicting the outcome of the photograph with the help of a
good, hand-held light meter. The bright
light, outlining the profile of the face and the hands was purposely chosen at
+2 1/2 (2 1/2 stops over). This was
determined with an incident light reading of just the main light source and
then opening the lens by 2 1/2 stops.
The rest of the face needed to be quite dark, but also needed to show
detail. For that an underexposure of -2
1/2 stops was chosen. This again was
done with an incident reading by adjusting the intensity of the light source
until it registered –2 1/2. This
photograph was actually shot in a studio with all white walls and a white
floor. No black background material was
used. The subject was approximately 30
feet from the background. With that
distance, so little light reached the background that the reflective meter did
register an underexposure of almost 3 stops.
In the original enlargement one can actually see a slight separation
between the dark part of the hands and the background which is ever so slightly
lighter. This kind of control would not
be possible without a good, handheld light meter offering both incident and
reflective reading capability, and certainly no automatic metering system,
however sophisticated, would allow this to be done.
These two examples are
much less complicated. Only one soft
light source, an umbrella, was chosen to illuminate the subject. For an almost white background, its lighting
was set to render an almost three stop overexposure in the first example while
a reflective reading of the background rendered a neutral density background in
the second photograph.
A similar technique was
applied for the above color photograph.
Via incident reading the correct exposure for the subject and subsequent
camera settings were determined. A spot
with blue gel was used on the background which was positioned such that it
would reflect off a piece of black plexiglass on which the subject was
positioned. For the relatively intense
blue an overexposure of one stop was chosen.
With a reflective reading of the reflection off the plexiglass the
background light was adjusted until this exposure was reached.
Could the same background
exposure be achieved with an incident reading?
Not at all. While an incident
reading can determine the relative brightness of the light source, it cannot
give any information about how much of that light is actually reflected by the
background material. A reflective meter
on the other hand will read exactly that.
Therefore, to have the total control described above, both incident and
reflective meters are essential.
It must also be mentioned
here that a lot of light meters require the removal of the incident sphere and
replacement with a reflective reading attachment. In situations as described above, those
meters have proven to be very cumbersome.
Light meters which allow the incident sphere to slide aside and thus
changing to a reflective reading have proven to be much more practical.
Could the subject exposure
be determined with a reflective meter?
Yes, but it is much more difficult.
Especially with portraits, we have to deal with a large variety of skin
tones. Most Caucasian skin tones are too
light and would lead to a slight underexposure with a reflective reading, just
as very dark skin tones would lead to overexposure. An incident meter on the other hand will
automatically render exposure settings which will render the skin tones
accurately, regardless of how bright or dark they might be. An incident meter will render true tonality
in both color and black and white.
A good example is the
photograph below. A simple, diffused
light source (umbrella) was used as the only form of illumination. This, of course, rendered a mostly black
photograph. The incident meter, aimed at
the light source easily gave the correct camera setting. Most reflective light meters would have
failed with the possible exception of a spot meter. Any automatic exposure control would have
been fooled by the mostly black scene, including any of the computer controlled
matrix metering systems, regardless of manufacturer.
The question is often
asked about where to aim the incident meter when multiple light sources are
used. That ultimately depends on the
approach to lighting. I know that a lot
of photographers set up lighting, especially for portraits, by establishing
certain lighting ratios, which then are set up with the help of a light
meter. I prefer to exercise full visual
control. It is my philosophy that no
meter “knows” what lighting is right for an individual. Further, I strongly feel that the lighting
should be set to accent the individual.
Preconceived lighting ratios can’t always do that. Therefore, I set up lighting to best accent
the task at hand. Once I decide on a
certain lighting, as in the above examples, I start with the main light and
then use fill as necessary. With other
words, I adjust the lights until they look good. Then, for the reading, I aim the incident
meter toward the main light source, may it be a soft box, umbrella, scrim,
window or any other. That will give the
correct camera settings, and everything else will literally fall into place.
A word of caution about
the measuring range of the light meter.
Using large format cameras often necessitates very small apertures like
f/32 or f/45. To apply the same control
as described above to get a true white background would subsequently require a
light meter capable of reading apertures of f/90 or f/128. While some light meters are capable of doing
this for continuous light, few are able to do the same for electronic
flash. The same also applies to maximum
exposure time. While very long exposure
times usually are not necessary, it is however, a good idea to have ample
reserve in this respect in order to be able to handle all photographic
situations. The longest exposure time I
ever needed to use was one hour.
The above photograph is
not computer manipulated. It is a double
exposure of the microscope and a carefully positioned rear projection screen
with the image of the earth projected onto it.
The exposure for the microscope, once lighting was set up, was
determined with an incident reading and the first exposure was done accordingly
with just a black background. After
carefully positioning the rear projection screen, a reflective reading of the
projected image was taken. An incident
reading will not work in this situation since there is no illuminating light
source. Instead an actual reading of the
true brightness of the projected image had to be taken, which can only be done
with a reflective meter. The meter was
placed flat against the rear projection screen over the area showing the brown
area visible in the center. No
adjustments to the reading were necessary because this color of the earth is of
neutral density. This reading was then
used to expose the background.
A common practice among
professional photographers is to use Polaroid film or to use the viewing screen
of digital cameras to verify exposure.
While there is nothing inherently wrong with that, it is still
beneficial to be able to take an accurate and reliable exposure reading since
some photographic situations simply don’t allow for enough time to do so. The photograph below is such an example.
I decided to use tungsten
film to accentuate the blue sky (a tungsten setting for the white light
adjustment on a digital camera would do the same). A careful reading of the interior was used to
determine the camera setting. This had
to be taken via a reflected reading since no access to the interior was
available. For that an area of average brightness
was chosen. For an intensely blue sky
exposures of neutral to +1 are necessary.
At that time of day lighting changes very fast. To get the correct exposure, spot readings
were taken of the sky right above the building.
As soon as the sky density had reached the +1 level, exposures were
taken in short intervals until the sky darkened to neutral. These changes take place so quickly that no
Polaroid test exposure would have rendered usable exposure settings. Subsequently, none of this was done with the
help of Polaroid film or the almost instant feedback of the viewing screen on a
digital camera. But it does show how a
good hand held light meter can be an invaluable tool for total exposure
control. Yet there is more.
Many photographers use
seamless paper to achieve different colored backgrounds, and at times this is indeed
a good choice. However, colored gels can
in a lot of cases do very much the same, again with absolute control. In general, a white background material will
usually lead to relatively light, pastel colors since it does reflect a large
amount of the ambient light in addition to the background lighting. Gray surfaces are helpful in this
respect. If, however, really intense,
pure colors are needed, this is best done with a flat black background material
like black seamless. The same test, as
described above for backgrounds from white to black, can be done here. Regardless of the color of the gel, the three
stop over exposure will render white as a four stop underexposure will render
black. Exposure changes in 1/3 stop
increments will reveal the various color densities which can be achieved. This incidentally is repeatable with
virtually absolute accuracy if the same gels and background materials are used.
Photography inevitably
requires accurate exposure settings. The
more control we are able to exercise over these exposure settings, the better
the outcome of our photographs. Besides
the camera, the most important tool here is the photographer, his or her
knowledge about exposure control and the help of a good reflective/incident
light meter.
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All the built in meters in our cameras are reflective meters. It is my understanding that taking a reading off a grey card renders the same results as an incident reading. Wouldn't that allow us to avoid purchasing a hand held meter?
ReplyDeleteThat is basically correct. However, you would find it fairly inconvenient to hold your camera in one hand and the grey card in the other and then position the card correctly to get the reading. To take an incident reading, it is necessary to make sure that the light falling onto the meter is the same as that which illuminates the subject. With a grey card in one hand and the camera in the other this could be very difficult at best in many situations.
DeleteAre you recommending a Gossen meter over a Sekonic?
ReplyDeleteNot necessarily, it depends on which Gossen and which Sekonic meter. In case of the two examples, I would definitely chose the Gossen, simply because of the convenience of switching between the two meter modes by simply moving the incident sphere to the right or left. The Sekonic meter requires the purchase of a reflected reading attachment which has to be installed after removing the incident sphere. I have heard from many photographers that lost one or the other attachment after removing it from the meter and then forgetting where they put it. This is easily done when concentrating on a shoot rather than plumbing around with equipment.
DeleteWhat hand held meter do you use for yourself?
ReplyDeleteI have several. My favorite is an old Gossen Luna Pro F. It will take reflected and incident readings with both continuous light and electronic flash. It also has the convenience of switching from reflected to incident readings by simply moving the incident sphere to one or the other side. For ultimate sensitivity I also use an even older Gossen Luna Pro. It is capable of exposure times up to eight hours. Both have the additional advantage, for me anyway, to have analog read outs. Also, both meters will accept a multitude of accessories. One that I use quite frequently is a narrow angle attachment which changes the normal reading angle of 30 degrees to 15 and 7.5 degrees (most other meters have an angle of acceptance of 45 degrees). This allows me to take reflected readings of relatively small areas even from a distance.
DeleteWhat other accessory attachments are there?
DeleteFor my light meters they are only available on the used market now since both meters have long been discontinued. For the Luna Pro there was also a 1 degree spot attachment as well as a flash reading attachment. For both meters there were a darkroom attachment, allowing to take spot readings of the enlarged negative for accurate exposure settings, a microscope attachment, an attachment to allow spot reading when doing copy work, an attachment to take spot readings off the ground glass of large format cameras as well as an attachment that allowed the meter to read through the eyepiece of a focusing magnifier for large format cameras.
DeleteDoes any other brand of meter offer such a variety of accessories?
DeleteNone that I am aware of.
Delete