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The spot
meter:
This little
gem allows you to determine the brightness of a small circular
area the diameter of the cross hairs. However it does not tell
you what exposure you need to use, the reading must be interpreted
by the photographer.
The meter
will tell you how close to "middle toned" the area
under the cross hairs is. If you aim the cross hairs at a gray
card (which is exactly middle toned) the meter should read "0EV"
letting you know that the spot meter believes it sees something
that is middle toned.
If you are
aimed at a gray card, and the meter does not read 0EV, you need
to adjust the exposure until the meter reading does say
0EV.
What if, however,
we aim the spot meter over a piece of white paper instead of
a gray card?
Since white
paper is 2 stops brighter than a gray card (or +2EV brighter)
the meter should read +2EV. If the meter reads, for example +1.3EV
we know we need to adjust the exposure time until the meter reads
+2EV.
This will
make the exposure longer, resulting in a brighter picture that
will be properly exposed for the white of the paper. Which brings
us to...
The zone
system (for exposure):
The zone system
is simply a way to assign exposures to familiar things with a
known brightness. We have already covered two examples.
A gray card
being middle toned and showing up in the meter as 0EV, and a
white piece of paper, which will show up as +2EV.
But what about
other items? And how does the zone system apply to them?
The zone
system is divided up into 10 zones.
From zone
0 to zone 9:
 Zone 0 = -5
EV = Pure black no detail
Zone 1 = -4 EV = black, only a
hint of detail
Zone 2 = -3 EV = black with some
details visible
Zone 3 = -2 EV = dark but with
full detail visible
Zone 4 = -1 EV = dark toned with
full details visible
Zone 5 = 0 EV = middle toned,
full details visible
Zone 6 = +1 EV = light toned with
full details visible
Zone 7 = +2 EV = White with some
detail visible
Zone 8 = +3 EV = White with a
hint of detail
Zone 9 = +4 EV = Pure white no
detail
The image
above shows the same piece of fabric at different exposures.
Each exposure is one full EV/stop from the next.
Now that we
know how the zones of the zone system are divided up, let's assign
some familiar things we might see in a typical scene to the zones:
Zone 0 =
-5 EV
Pure black, darkest shadows, deep cracks, black nighttime skies
Zone 1 = -4
EV
very dark shadows
Zone 2 = -3
EV
dark shadows, black cloth, black plastic, black/dark brown hair
Zone 3 = -2
EV
Brown hair, blue sky, dark green leaves, shadowed dark skin.
Zone 4 = -1
EV
Dark skin (generally)
Zone 5 = 0
EV
Gray card, stone washed blue jeans, shadow on light skin
Zone 6 = +1
EV
Light skin
Zone 7 = +2
EV
Paper, snow, white sand, white walls, white t-shirts
Zone 8 = +3
EV
An overexposed window, pure white backgrounds
Zone 9 = +4
EV
Specular reflections, lights
So if we see
something in the scene that has a known brightness, we can spot
meter off that object to get an accurate exposure.
For example,
we are out with some friends, and they stand next to a fountain.
One of them is wearing a white t-shirt. You want that t-shirt
to look a bright clean white, so you meter off the shirt, set
the exposure until the meter reading just shows +2EV and snap
the picture.
You can be
very confident that the exposure will come out good.
But now we
have an additional tool to help us with exposures, we have...
The histogram
(in camera or in PS):
 The histogram is a graphical
representation of the distribution of tones in the scene. Far
left represents pure black, and far right represents pure white.
The fabric
samples shown above have a distinctive histogram (right).
You can see
that each zone has it's own corresponding peak in the histogram.
Now lets take
a photo using the spot meter and the zone system and then analyze
the photos exposure using the histogram.
Here I have
a pair of stone washed blue jeans and a t-shirt. I spot metered
off the t-shirt and set the exposure so that the meter read +2EV
(zone 7) and then took the picture (left).
The photo's
exposure looks just the way it did in real life, this is a good
sign.
Now lets look
at the histogram and see how the image data is distributed:
 You
can see the peak on the right hand side corresponds to the +2EV
and this would represent the t-shirt in the photo.
Look at the
wide peak centered on the 0EV mark.
That would
be the stone washed jeans, but what is that smaller peak just
to the left? We can see it is about -.5EV, and you will also
notice there is a dark "Wrangler" label visible on
the jeans.
The small
peak represents that small darker label, and we now know how
bright it is compared to both the blue jeans and the t-shirt.
We can also see that the scene was metered accurately and all
we did was apply the zone system using the spot meter in determining
what our exposure was going to be.
The histogram
lets us analyze an image after we have taken it to see how well
the tones in the exposure match the actual tones in the scene.
As you become
more familiar using the histogram, you will be able to quickly
determine if the image has the right exposure and the tones are
distributed the way they should while viewing the live histogram
on the camera.
In practice,
all of this works quickly and accurately once you get the hang
of it. If you master the techniques, your exposures and productivity
will thank you for it.
This article ran originally
as a post to the DPReview Sony Talk Forum. Reprinted with permission.
Shay's
galleries will inspire 707/717 owners. Check them out:
Sony F707
Gallery: http://www.shaystephens.com/portfolio.asp
F717 Observations: http://www.shaystephens.com/f717.asp
More will
be here as the Sony Zone pages evolve.
-iNova
PS: As
experience grows with these cameras, so will this review and
the Sony eBook. Available now on the order page.
Article © 2002
by Shay Stephens. All rights reserved. Images and screen captures
by Shay Stephens.
Site © 2003 Peter
iNova. All rights reserved. Do not replicate or link to images
without permission. All photos by Peter iNova.
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