Outdoor Exposure

Transcription

Outdoor Exposure

The Outdoor Exposure Dilemma - Matching Scene and Senor Range
Any photograph is both a technical exercise and a creative one and we
all come to the forum with differing experience and frames of
reference. My foundation in photography was teaching myself the zone
system from Adams Books with B&W film and prints while in college. I
wound up doing more photography than studying and quit college to
work in photography. I saw a help wanted ad in the Washington Post
in 1972 which resulted in a close encounter of the best kind with the
wedding business working for Monte Zucker, where I learned the
creative and business side of photgraphy. I learned I like the technical
side of photography more than dealing with people, so when when a
new opportunity crossed my path I became a lab technician at National
Geographic doing photographic reproduction for its magazine, maps
and book and within year was also teaching reproduction photography
at a local college - I went there to take classes in printing technology
and they offered me a job teaching the camera class I took. I went on
to work in offset printing and magazine production, which has far more
variables that photography, and that led to a job in the Foreign Service
managing overseas printing and publishing for USIA and State. I
continued to explore photography, but as a avocation on my terms,
not as a business. I lost my darkroom when I moved overseas and for
many years shot mostly underwater while diving in the Philippines.
I've used dual flash since seeing its benefits shooting weddings with
Monte in the early 1970s. In the years since I used pairs of manual
Vivitars with optical slaves with 35mm and medium format film
cameras and several iterations of digital: Kodak DC290 (selected in
part because it has a PC connector), Minolta D7Hi which as has an EVF
and no sync limit, and then a Canon 20D. Even after the switch to the
20D i continued to use the Vivitars, but after the D7Hi which sync'd at
any speed the 1/250th limit of the 20D was crippling, in the creative
sense. I bought into the Canon flash system quite skeptically, primarily
to get the benefits of high speed FP sync outdoors. I didn't get very
predictable results until I figured out how Canon evaluative metering
works and developed a new shooting strategy.
Using manual I was constantly thinking about flash distance, exposure,
aperture. With ETTL I found the quickest and easiest path to perfect
exposure is:
1) Set camera to its "I think this is right" baseline EC = 0 / FEC =0
© Charles E. Gardner - http://super.nova.org/DPR/
2) Compose and shoot
3) See what happens - evaluate using clipping warning and histogram.
4) Adjust as needed
By working that way in one metering mode, always starting from the
zero baseline I quickly came to understand how the camera metering
worked. It in not always perfect, but when it missed the results are
predictable. That the shot the same way and you'll get the same
results.
When doing testing I wanted so way to evaluate highlight exposure
visually in the playback just based on when detail is blow. I grabbed a
white towel because it has texture that disappears when overexposed.
When looking at the files on the computer and the camera at the same
time I discovered that clipping in the towel in the camera playback
accurately predicted when highlight detail was lost in the RAW file. The
towel image in the clipping warning became my "Canary on the
Coalmine" for exposure and it became a no-brainer to get perfectly
exposed file in the highlights. Raise exposure until clipping occurs then
back off 1/3 stop.
I learned how to flatter a face with light from Zucker. Its mostly a
matter of getting light in the eyes, a mask pattern of highlights on the
front of the face which mimics how we see faces in natural light most
of the time, and avoiding any distracting poorly placed shadows. The
nose sits between the eyes and mouth and can become a huge
distraction if poorly lit with a long dark shadow hanging off of it. Watch
the nose shadow as the key light moves and you get flattering lighting
when the nose looks like a nose instead of a sundial at 3 or 9 o'clock.
How much of the sundial shadow shows at high noon? Not much. How
much do you notice the nose in a butterfly lit full face shot? Not much.
Being very intuitive I see the connection in thing like that.
When at NGS one of my jobs was shooting map relief from hand drawn
artwork. To create the illusion of a mountain the artist just rendered
the shadow the mountain would cast when the sun was at a 45 degree
angle. Higher relief casts longer shadows. The highlighted side of the
mountain didn't need to be drawn because the brain, seeing he
shadow pattern perceives the shape from the shape of the shadows.
That optical illusion is also how lighting patterns on a face work.
Moving the key light so it causes the nose shadow to fall along the
base of the nose and with the tip shadow falling over the top of the
nostril makes a nose look natural because the shadow winds up
looking like half of the nose. Short lighting over an oblique angle to the
camera makes a face look slim because only the front is highlighted. It
makes the face look symmetrical because the camera angle reveals
the shape on the far side, while the shadow border traces the same
line from corner of the eye to chin on the near side. Combined they
create an illusion that tricks the brain into thinking the face is
symmetrical even when it isn't....
The top photo is what I see in the bathroom mirror. That's the self
image most people who are not frequently photographed have. Mirror
the two sides of the face and the asymmetry becomes more obvious to
the untrained eye:
In the top I look like Nick Nolte's worst mug shot because the left side
of my face is very wide. The right side is less wide. I look best in a
oblique view which hides the wider side.
Photography is the art of illusion: capturing an image, then
reproducing it in a wide variety of ways all of which trick the brain of
the viewer into tuning out the real world and imagining that the
pattern of contrast on a print or screen is a real object or person and
they are in the scene watching it. That is the bigger picture goal for
any photograph, at least those I take.
What makes a subject composed and lit one way look compelling and
real in a photo but in some other light look fake has more to do with
how human vision an the brain work than f/stops or shutter speeds.
The learning curve for operating the camera is a short one and easily
mastered. The longer climb is developing an understanding over time
on a conscious level of how people sub-consciously process and react
to images.
In person our eyes react to the brightest thing in our field of vision,
constricting the pupils. The retina has a finite range of sensitivity and
our brains mentally tune out anything not in the center of our vision,
so when looking at a distant landscape the brightness of the sky will
make our pupils constrict and we loose the ability to see details in the
shadows. But when close enough to see the light and dark areas
separately our pupils adjust to whichever we are looking at an the
short-term memory of the brain makes us think we are seeing
everything in the same light with detail. Part of learning to "see"
photographically is understanding and being able to pre-visualize how
the camera will record thinks differently than our eyes see and our
brains imagine. Adams called that process "pre-visualization".
This is what the camera captured....
This is what I saw it could be by known how the camera would record
it, how bland it would look, but also how it could be manipulated to
create the same emotional reaction in the mind of the viewer which
attracted me to take the shot...
What controls the reaction and changes it when looking at those two
images? The difference in contrast. The eye roams around looking
everywhere is attracted by contrast. It is a basic survival instinct. In
real life contrasting movement is the "danger" trigger. In a still photo
it is contrasting tone, color, sharpness, size, shape, etc. Contrast
manifests itself many ways but what is quite predictable is that what
contrasts the most with the overall background in a photo will pull the
attention of the viewer towards it.
That is how we react sub-consciously to the world round us and the
photos we view. Thus an important part of mastering the art of making
a really effective "Wow" factor photo is consciously understanding
what leads a viewer's eye around a photo and putting the message of
the photo, the visual equivalent of a punchline, in the area than
contrast will attract them to. On a dark field it will be the brightest
area, on a light field the darker and more colorful areas will attract the
eye.
Stage lighting uses contrast to guide the viewer in the audience to
what is important. With the stage dark and the spotlight on the star in
the front of the stage you don't even notice all the guys dressed in
black moving around and changing the set or the next scene. But for
Swan Lake the stage is brightly lit and awash with a sea of white
dancer's save one black one. Which of the 100 dancers attracts the
most attention? The black on which contrasts. Does that example
provide any clues how to make the delivery of a message in a photo
more effective?
The genius of Adams' iconic photos of Yellowstone is that many reveal
in the photo more detail than would be seen by eye in person from the
same distance. Adams understood human perception and how to
predictably and completely control the technical aspects of his
photographic medium so is far away landscapes reveled even more
detail than seen by eye from the same spot. The contrast of the scene
was first manipulated with filters. B&W film is more sensitive to blue
than the human eye, so any photo with a sky, even when correctly
exposed would look too light in tone on the print. Thus it was SOP to
keep a yellow filter on the lens outdoors to make the sky appear
normal. Adams took things a step further by using a red filter which in
B&W will make the sky appear darker than normal and anything
reddish - like the majestic purple mountains - appear lighter and more
luminous. Adams photos work on an emotional level because he knew
how to control contrast in a way which would predictably affect
perception and emotional reaction to the photograph.
Unfortunately B&W film is the only commonly used photographic
medium which can be manipulated in a way that will record detail over
the full tonal scale in any contrast AMBIENT lighting with a single
exposure. That is accomplished by changing the contrast of the
negative with development to match the range of the scene to the
range of the printing paper. The range of the printing paper, the
output medium, is the limiting factor. The same is true with color film
photography. A color negative can record a greater range of scene
luminance than the color paper can reproduce.
Digital is similar in result but for a different reason. A sensor is like an
array of water buckets. In the highlights the get filled with a fire hose,
in the shadows with an eye dropper. What determines optimal
exposure is when any of the buckets is filled to the brim. The problem
with respect to capturing a scene with a digital camera is that the
"buckets" in most of the darker areas are still mostly empty when
those in the highlights are filled and the shutter stops the exposure.
Thus when we expose for normal (as seen by eye in a photo)
everything darker in tone in the mid-tones (like a face) seem too dark,
and deeply shadowed areas have no detail at all, just rainbow speckles
caused by residual electronic static (noise).
The range of a camera sensor is very easy to determine with just a
gray card. Put the card in flat light with the camera on a tripod with a
fast lens. First set Custom WB on the card so all channels will clip at
the same time. Open the lens to is widest aperture (e.g. f/2.8) and
adjust shutter speed until the entire gray card clips in the camera
warning. That defines the upper end of the sensor range. Speed up the
shutter so the card is 1/3 stop below clipping, the value of textured
whites, then closing the aperture in one stop increments (2.8, 4, 5.6,
8, 11, 16, 22) shoot a series of frames. In the camera histogram,
which represents the range of the sensor, the spike from the card
move left from just kissing the right edge at 1/3 stop under clipping
until it hits the left edge. If the smallest aperture doesn't move it all
the way to the left speed up the shutter in one-stop increments until it
does.
The illustration above shows the results of a test like that I did a few
years ago with my 20D. The red lines indicate where the spike from
the card wound up with each exposure. The number is the eyedropper
value of the channels (0 - 255) and the tone patches were cut and
pasted from each file to show how each exposure rendered the card.
From that test I was able to determine the camera could record about
6-1/2 stops of scene range with detail I could see in a typical image (a
range of 245 in the highlights to about 30 in the shadows). It also
gave me a tonal map of sensor response. Now I know what each point
on the histogram scale represents as a gray scale value. As you can
see from the spacing of the lines the response is not linear.
Outdoor scenes have varying contrast ranges. Put a full range target
like a MacBeth in flat overcast light and the difference in brightness
between the white and black patches, measured with a 1-degree
reflective meter might be 7-8 f/stops. The same card held in direct sun
but angled so the black patch is shaded by the card might measure 12
stops between the patches. The character and angle of the sun affect
scene contrast. Here's a target capture mostly in direct sun hitting it
from the front, exposed for the highlights in the white towel...
Looks pretty much as seen by eye in the same light, but if it were eye
sockets in the shadows instead of the card they would seem very dark.
Perceptual reaction is influenced by scene content and context of the
background lighting. For example here is the same target, exposed the
same way for the highlights in the towel..
The light is the same the exposure goal was the same (detail in the
highlights), yet this shot appears to be, perceptually, way
underexposed. Why? Because the contrast of the scene is now much
greater than the camera is able to record.
When confronted with such a situation what a photographer will decide
to do is adjust the exposure so what is most important perceptually
looks normal. That is a very logical and valid strategy in ambient only
situations, but what happens when the face in shadow is used is the
baseline for correct exposure the camera sensor will no longer be able
to record detail in the brightest highlights. So what the photographer
does, often without realizing it is to expose for the middle and let the
end values fall where the sensor puts them.
Averaging meters are calibrated to do the same thing. If a gray card in
a backlit scene was measured close-up with a reflective meter and the
exposure reading used to take the shot the card would be reproduced
as seen by eye (putting aside the 12 vs 18% issue for the moment).
Step back and meter the entire seen and very likely the average of all
the light in the scene will produce a similar reading and the resulting
photo will LOOK NORMAL - as seen in person. Put in both cases the
photos will have blown highlights in lighter areas!
Now here's where I part company with most it seems. Most
photographers who have never used the zone system to shoot and
make B&W prints have never in their life reproduced a sunlit scene
WITH DETAIL EVERYWHERE. Their "normal" for a photo is correct
middle tones making them look the same as seen in person, the fact
that highlight and shadow detail is lost in the print or screen image is
also accepted as normal.
I've learned to use the natural light and flash together in ways so the
results appear natural (as perceived by eye) with detail over the entire
tonal range.
In that photo, taken as part of a high speed flash test / tutorial I
started by exposing for the ambient highlights, which required - 2 EC
in Av mode, getting the dark looking shot above, then simply reached
up an turn on my 580ex flash on the bracket in high speed FP mode. It
was set on FEC = 0. The evaluative metering sorted out the balance
and correctly exposed the foreground with detail in the highlights just
a bit darker than those sunlit, just as the lighting would be perceived
by eye.
The classic dilemma in photography is a face in the sun at such a high
angle that the brow shades the eyes. Adding flash to the face in that
situation will not change the contrast between the bright forehead and
cheek and those dark orbits because hits both areas equally. Yes the
shadows will get lighter, but if the cheek is already correctly exposed
in the ambient you've likely already blown the detail in the white shirt.
Adding flash will blow out the face highlight and the shirt even more.
Increasing shutter speed will get the highlights darker, but it will also
darken the eyes. You can keep pounding flash to the face to the point
where the flash overpowers the ambient but the eye sockets shaded
by the brow will still be darker than the cheeks and forehead.
Why?
We started with the sun as the key light. The fill to the extent there
was any in the eyes came from the sky. Shade of sunlit objects meters
about 3 stops less than the sunny side. The camera range is 6-8 stops
and when the white stuff in the scene is exposed for detail - 3 stops
falls in the middle of the sensor range -middle gray.
Adding flash fill couldn't reduce the contrast difference between the
cheeks and eye because it added to both equally. The shadows are
made lighter and it looks more normal perceptually, but the highlights
also get lighter. That is accepted perceptually, up to a point where it
seems fake. From the technical perspective really bad stuff starts to
happen. Skin reflects more red than blue and green. So when
overexposure starts to occur on skin the red channel is blown first and
with it goes all the subtle highlight detail and shape defining contrast
in the highlights. The skin highlights will take on an odd, yellowish flat
look which to the untrained eye appears to be a white balance
problem. It is, but one caused by blowing just one of the three
channels. The fact that digital camera record images as separate red,
green and blue pixels it the root cause of the problem, and there's no
solution except exposing for highlight detail.
When we finally add enough flash to overpower the sun, the role of the
ambient light changes. The flash now become the dominant source the KEY light creating the highlight pattern and the sun and sky
become FILL in the technical scene of being what is illuminating
everything not highlighted by the KEY. But the key light is overlapping
the ambient light and the eyes will still have less light in them than the
cheeks and look darker in the photo.
The solution to the problem getting light in the eyes in that situation is
simple: raise the chin so the brow isn't shading eyes! It is what you'd
do indoors in the studio if the brow was shading the key light from the
eyes. Unfortunately that doesn't work very well outdoors for a practical
reason: bright light makes people squint and squinty-eyed people are
not very attractive.
Photographers learned by trail and error to solve the dilemma of
unflattering contrasty lighting patterns on sunlit faces by putting the
subject's back to the sun, or alternately putting them entirely in the
open shade. That was the advice for shooting people outdoors in the
first Kodak "How to ... " books I read in the late 1960s. The first
strategy doesn't solve the contrast dilemma. Exposing the face to look
normal will blow the highlights and give the subject a nuclear halo, but
perceptually that's acceptable and in fact it looks very much in context
to the feeling of backlight on a sunny day.
The second solution, open shade, is a better one in the technical sense
because in open shade the light is even and will better match the
range of the sensor. But open shade like any flat lighting doesn't
create enough light / dark contrast to make things look "normal" in a
photo. Stop here and consider that in person much of our sensation of
shape comes from our stereo vision and the eye shifting focus from
foreground to gauge shape. That's the problem in my gear photo as
seen by eye and shot. But I was able to see beyond what both what
my eyes saw and what the camera recorded to create an image in
which I enhanced the illusion of shape and guide the eye path of the
viewer over the shape with contrast. In Adam's parlance, I previsualized the outcome. Yes in that case the manipulation was done in
Photoshop. I could have done it by using artificial lighting, but I didn't
want to be bothered and knew exactly how I could make it look before
pressing the shutter.
The goal of the exercise isn't recording what is there faithfully. The
camera can't do in most situations due to its physical limitations. All
photography is just a form of optical illusion and the craft part of the
exercise is learning how to make the quarter disappear out the hand
and seem to come out of the ear.
When a subject is placed in backlight with no sun on their face, it
creates a much better illusion of overall 3D shape of the person and
the depth of the scene, but puts the face in really bland flat light
coming from the sky. But if the backlight from the sun is combined
with one flash over the camera the combined effect is illusion of shape
overall from the backlight, and modeling on the face from the flash
acting as KEY light creating the shade defining highlight pattern over
the sky fill...
On a perceptual level the contrast of the dark hair on the light
background of the sunlit river -- selected so the white clothing would
not distract from the face -- is really what first attracts attention
tonally and pulls the eye to the center to find the face framed by hair.
The shape of the face is defined normally because I raised the flash on
a bracket so it hit the face at a downward angle from overhead, just
like natural light does. It defines shape and guides the eye in two
separate ways which work together to pull the viewer to the eyes and
mouth, make eye contract, and react emotionally. Because the face
contrasts and there isn't much else in the photo to distract attention
off the face attention stays on the face longer...
The sunlight acts at the "kicker" and the flash is key. The difference in
flash looking fake or realistic on a face is a result of how it is
positioned. If the flash is placed near the lens axis is will not create
change the contrast pattern it will just add more flat light. The pattern
in the shot above was the result of raising the flash on a bracket, a nobrainer strategy wedding shooters have been using since the 1960s to
flatter faces taken with a single flash. I've always used a bracket with
flash because I learned to use flash with a bracket and immediately
understood how and why it improved the lighting pattern.
In the above shot the fill on the face comes from the sky and light
reflected from the white clothing (it contributes quite a bit actually).
The fill is 3 stops below the sun, but works OK because most of the
face is highlighted, the shadows frame the face because the light is
centered and there is no dark nose shadow hanging off sideways and
distracting.
But change to an oblique view where the face will be mostly in shade
and the contrast of sky fill alone will look too harsh. Same lighting,
difference perception of the lighting because more of face is in
shadow. The solution to make the lighting look softer is the same
you'd use indoors with flash: add fill to lift the shadows and reduce the
contrast of the scene to match that of the sensor. I use fill near the
camera axis because it reaches all the shadows and there are no
unfilled voids. With my Canon flash the flash on camera becomes the
fill and the off camera flash the key light highlighting the front of the
face.
First I adjust ambient so the sun as "kicker" doesn't nuke the
highlights. That's simply my preference to prevent the hair and the top
of head from being a distraction. I just want enough light to define
shape and separation, but not so much the contrast pulls attention off
the eyes and mouth. Exposing that way makes the face look very dark
because the contrast exceeds the sensor. So first I lift the sky lit
shadows with the flash on camera as fill, then overlap the off camera
flash over both. The shot above was done to illustrate the results
direct flash produce with an oblique angle and "neutral" fill / key
strategy in backlight.
The sky wraps around the face 180 degrees so there was already
wonderful soft light on the face. The problem comes when the sunny
parts are kept below clipping - the camera renders it darker than seen
by eye. Neutral flash adds light but doesn't change the rendering /
modeling of the object it hits because it is flat. Flash on the bracket
isn't totally shadowless because it comes from above the face, but
think about it: so does the fill from the sky!
The goal of the exercise is natural looking lighting and the flash on the
bracket mimics the angle of the natural fill. Actually it does a better
job. Put a face in open shade outdoors at eye level and look closely at
the light on the face. In most cases the eye sockets will be darker for
the same reason they are in direct sun: the light is coming from so
high an angle that the brow shades the eyes. So even when the face is
in backlight it needs to be raised up into the sky so the fill reached the
eyes. That changes the camera angle to the face, Bring a small 4-6ft
ladder along or finding a rock or table to stand on and get both
flattering light and camera angle.
Once the flash adds enough fill to lift the shadows lighter and make
the lighting seem softer. Soft/hard is just an optical illusion created by
the tone of the shadows, just as shape is mostly an illusion created
from the clues the shape of the shadows created by the key light
position provide. The final step is providing shape to the face by
overlapping the key over the combination of sky and flash fill.
The net effect is soft shadow transitions on the face, even with direct
flash. The soft skylight gets all the credit. The neutral fill lightens the
shadows making the overall pattern seem softer than sky fill alone
does and the off camera light models the shape of the face in a natural
looking way, also assisted by the soft skylight coming from the same
direction. That's the difference shooting outdoors. The sky boosts and
softens all the lights aimed at the front of the face. Huge diffusers
aren't really needed. Outdoors diffuser size mostly affects the how
specular the highlights on damp/ oily skin look because relative to the
huge sky they are very small and don't really change the shadow
transitions.
Fill controls shadow tone and shadow tone creates the illusion of
softness. Learning to control fill and match the range of the scene to
that of the sensor is the key to making photographic images seem
more like what is perceived by eye in person. That's the goal I work
towards in every shot I take.

Outdoor Exposure

Transcription

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