Metering for Correct Exposures
A short cut:
Please click on your camera's model
at the bottom of this page for your camera's free spot metering cheat
remember: The difference between point-and-shoot and using
your camera in "spot" mode and manual is that you MUST know to
dials on your camera in Manual Mode:
1) Aperture, 2) Shutter speed, and 3) set exposure to spot / Partial
to use a Spot Meter? What is Spot Metering?
How to use spot meter?
Exposure, by definition, is the determination of the amount of light to reach the
film in order to produce a correct image. In other words, to have a correctly exposed
image we have to have the exact amount of light entering the camera in order to register
the correct image on film. Remember that light is the most important element of any
photograph. Without it we have nothing. With too much of it you have an overexposed and
washed-out image. With too little of it you have a dark and underexposed image. In neither
case can we have an image that would truly represent the subject.
A simple and
Step outside and point three different
brands of cameras (Nikon, Canon, and Pentax) set to the same ISO at the same complex (multi-toned) scene. Please make sure your
exposure mode is set to "Manual" and your shutter speed (exposure time) is set
to the same value (say 1/125 sec.)
When each camera indicates a normal exposure (needle/index pointer in the middle of
'+' and '-', usually a "0") there are three possibilities:
1) Three cameras show exactly the same normal exposure (say 1/125 sec. @ f-8)
2) Two of the cameras show the same normal exposure and the third camera's reading is
different (say 1/125 sec. @f-8, 1/125 sec. @ f-8, and 1/125 sec. @ f-5.6).
3) All three cameras show a different normal exposure readings (say 1/125 sec. @
f-11, 1/125 sec. @ f-8, and 1/125 sec @ f-5.6)
Considering there is only ONE
technically correct exposure for that specific scene, in
NONE of the
above cases the unskilled photographer can be sure which of these readings would produce a
Most cameras use some type of logic circuit to determine a subject's exposure.
Each of these designs is good at capturing certain types of images. Considering that we
live in a mass-produced world, no one can come up with a metering pattern that fits your
exact subject every time. Since this is a book about spot metering, I will
not bother you with different patterns, complex math, and their confusing details. The
bottom line is that with all of these metering systems, it is the meter that determines
the final exposure and not the unskilled photographer.
A spotmeter is a very narrowly angled meter capable of giving an exact exposure
(not necessarily a correct one) from a simple subject (preferably the most
important part of the subject). Examples of simple (one-toned) subjects are a piece of white paper, a uniformly
lit wall, a forehead, snow, or a portion of the blue sky. Depending on the
tone/density (removing color from the simple subject) of the simple
subject (whether it is white, light gray, medium gray, dark gray, or
black), usually this exact exposure (often referred to as the Normal
Exposure) is changed at
the discretion of the skilled photographer before the picture is taken; this
means the photographer
manually overrides the meter's reading by changing the shutter speed and/or
the aperture opening to create his or her own desired image. The
philosophy behind this simplified technique is that "if an important
tone of a subject is correctly exposed, the rest of the tones follow and
the entire image will be correctly exposed."
This is the "mind over meter" scenario.
Spot Metering, unlike broad-angel metering used on many cameras, will always provide you
with a consistent (and not necessarily correct) exposure. This consistency will give the skilled photographer the
starting point, or the base that he or she needs to create the desired image. To
understand how our on-camera spotmeter functions, we must educate ourselves with camera
basics and general exposure.
To further your understanding of
the spotmetering technique with specific camera examples, please refer to any of
the cheat sheets on the home page.
When to use a spot
The spot meter is used when the
photographer wants to get exactly what he or she is looking for. With all
other metering systems, when photographing a complex (more than one tone) subject, one can
never be sure of the exact outcome. Other metering systems lend themselves
to subjects that are of average contrast (short tonal range). In cases if
a person is in a hurry, for the average subject, the camera's "normal
exposure" generally is close enough to the correct exposure, the
less-demanding photographer will and can settle for this exposure.
Spot Metering is ideal if the subject has a long tonal range (high Subject
Brightness Range or high SBR), if the subject's background is much
brighter than the foreground, if the overall feel of the subject is too
bright or too dark, if the photographer is looking for the
"desired exposure" rather than the correct exposure (Silhouette), or in
the case of a subject with a long tonal range, where the brightness range
of the subject exceeds the contrast range of the film and the photographer
has to compromise and to favor one part of the subject over another.
Example 1: The above subject is mostly dark. A spot reading from the white petal provided the
photographer with the normal exposure (18% gray image tone with film
cameras/GrayScale Density of 128 in Digital). The photographer then increased the
exposure by 2 stops to assign a 72% white tone (grayscale density of 228
approx.) to the petal and let the rest of the tones to fall where they
Example 2: The above subject is mostly bright/white. A spot reading from the white petal
provided the photographer with the normal exposure (18% gray image tone
with film cameras/GrayScale Density of 128 in Digital). The photographer then
increased the exposure by 2 stops to assign a 72% white tone (grayscale
density of 228 approx.) to the petal and let the rest of the tones to fall
where they may.
Example 3: The above
mostly dark/black. A spot reading from the forehead of the model provided
the photographer with the normal exposure (18% gray image tone with film
cameras/GrayScale Density of 128 in Digital). The photographer then increased
the exposure by 1 stop to assign a 36% Light Gray image tone (grayscale
density of 178 approx.) to the forehead and let the rest of the tones to
fall where they may.
Example 4: The running
water subject is basically average. The lighter parts are balanced with the
darker tones and the overall image as you look at it is neither dark or
bright. A multi-toned / Matrix reading from the entire image will provide a
reading that is close to the correct exposure. In this case the spot
metering will not be necessary although it can be used to provide the
photographer with a reading that can be interpreted to provide the
of the terms used:
Our Tone Ruler -
Digital standard Scale is built around the 18% Gray image tone that when
correctly exposed will create an 18% gray image tone or a GrayScale density
of 128 (256/2). Each tone is ONE STOP away from its neighboring
standard tone. One stop approximates to 50 GrayScale Divisions in Photoshop.
Please note: You must desaturate (remove color) in Photoshop and use the
eye-dropper to measure image tones.
4.5 % Black image tone has a marginal detail
9 % Dark Gray image tone has a good detail
18 % Medium Gray has the best Detail
36 % light Gray image tone has a good detail (Caucasian Skin Tone -
72 % White image tone has a marginal detail
The Film Contrast
Range of a Slide Film and a Digital Film approximate to 5 stops.
Subject tones (Tone Ruler)