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Since the subject of metering seems to be a popular one, I thought
I’d share some of my thoughts on it for anyone who’s
interested. I’ll talk about metering studio flash, metering
ambient light with an incident meter, and metering ambient light
using your in-camera meter.
First, a few definitions. There are basically two different kinds
of light meters available: reflected light meters, and incident
light meters. A reflected light meter is the type of meter in
your camera. As the name implies, it measures the amount of light
reflected back from the subject. It can accomplish this through
several means, or metering patterns: center-weighted average,
multi-segment evaluative, or spot.
Center-weighted average is the type of metering pattern most
commonly found in older-style manual focus SLRs, and also in
a number of current medium format cameras. This type of metering
pattern reads the entire image area, but gives more weight (as
the name implies) to the central portion of the image.
Multi-segment evaluative meters read multiple segments of the
image area, then feed that information to a computer chip that
calculates the exposure. This is the type of meter found in virtually
all modern autofocus SLRs. It is widely thought to be more accurate
than the older style center-weighted metering, and in some situations
it is, but under many conditions they will produce pretty much
the same reading.
Spot meters read a very small portion, anywhere from 1 to 10
degrees of the image area, depending on the meter. The advantage
of this is that it lets you read only the subject of the image
without walking right up to them, or you can use it to read a
portion of the image that you know to be of a certain tonality
and determine your exposure based on that information. Spot meters
are found in most higher end SLRs. In fact, most of the more
sophisticated pro-oriented 35mm cameras allow you to choose between
any of these three metering patterns.
Spot meters are also available as separate, hand held meters.
These are not to be confused with hand held incident meters,
which are a completely different animal (although some of the
newer and more expensive Sekonic and Gossen meters contain both).
Spot meters are the hand held meters most often discussed in
Zone System books, and are widely used by Zone System practitioners.
Spot meters are particularly well suited to landscape and architectural
photography, but can also be used effectively for portraiture.
More on that below.
Now, if all this seems very complicated, please hang with me,
because by the time you get done reading this, I will have given
very simple, step by step instructions that anyone can use to
obtain consistent, accurate exposures. I just want to provide
some background first.
The thing that all reflected-light meters have in common, whether
they be center-weighted, multi-segment, or spot, is that they
are all calibrated to give you an exposure that will render whatever
they are reading as 18% grey. Now, not to make this more complicated,
but lately a question has arisen on whether it’s 18% or
13%. The common wisdom for a long time has been, and generally
still is, that it’s 18%. There are some, most notably Kodak,
and Bob Shell of Shutterbug magazine, who say it’s actually
13%. I suppose one way to find out would be to contact the various
manufacturers of cameras and spot meters, and ask them which
of these standards their meters are calibrated to. I don’t
know which is true, but for the sake of this article I’m
going to assume it’s 18% for the following reasons:
- This is the most commonly stated of the two
- 18% grey corresponds to zone V in the Zone system. The zones
are set up in full stop increments, and since 13% grey is one-half
stop from 18%, it falls halfway between zones V and VI. For this
reason, 18% represents a simpler frame of reference.
- A half stop is not a huge amount of difference, and is well
within the latitude of most color and B&W negative films.
And with such films, I’d rather err on the side of overexposure
than under.
Now, if you shoot slide film, half a stop will make a difference.
Most portrait photographers don’t shoot slides, so I’m
not going to concern myself with this. If you are partial to
slides or other finicky films, you may need to be pickier and
obtain the correct info either through your own testing, and/or
contacting your camera manufacturer.
- In portraiture, I would again prefer to err on the side of
overexposure, not underexposure.
So, for all the above reasons, and for the sake of simplicity,
let’s assume it’s 18% (if you disagree YOU can adjust
for this (-:). Now, if your in-camera meter is set to render
whatever it reads as 18% grey, you can see why just letting your
camera do all the thinking for you may not be the ideal approach
for portraiture, unless you like grey faces. Now, there are those
who prefer a silvery grey type of skin tone, and I’m not
being critical of that, and even for those who don’t, there
may be certain conditions when that may be appropriate. My guess
though is, that under most circumstances most of you would not
prefer to get 18% grey skin tones. This is why you need to take
more control of the process.
So, to summarize, the type of meter in your camera is a reflected
light meter. It reads the amount of light reflected back to the
camera from the subject. It tries to render whatever it reads
as 18%. That means that it can be tricked. If the dominant tones
in the picture are lighter than that, you will get an underexposed
image. Let’s say, for example, you are photographing a white
dog in the snow. The meter is going to see all that white and
try to render it as 18% grey, thereby giving you an image that
is underexposed by three to five stops. If you were photographing
a black dog on a coal pile, the meter would see all that black
and try again to render it as 18% grey, thereby giving you an
image that is overexposed by three or four stops.
How does this apply to portraiture? Well, if you are photographing
a light skinned subject, even if you meter off the face, that
face is still a stop or two lighter than 18% grey, so you will
end up with an underexposed image. If you are photographing a
dark skinned subject, and again you meter off the face, that
face could be (for the sake of discussion) a stop or two darker
than 18%, so you are going to end up with an underexposed image.
If you were to let your camera decide the exposure, the only
time you’d get an accurate exposure is if you were photographing
a medium skinned subject whose tone matched 18% grey! When you
consider the variety of skin tones out there, even among Caucasians,
plus the various lighting conditions one can encounter (like
backlighting), you can see that if you rely only on the camera,
you may get a lot of bad exposures.
Now that I have pointed out the potential problems with in-camera
metering, are there ways to adjust for this and get good results
with these meters? Absolutely, and I will discuss them shortly.
But first, on to incident meters.
INCIDENT METERS
Now, the incident meter functions in a completely different
fashion. It does not measure the light reflected from the subject,
it measures the amount of light falling on the subject. It does
not try to render everything as 18% grey, or any other tone.
When used properly, it measures the amount of light falling on
the subject, thereby allowing for an accurate rendering of all
the tones in the scene, within the capabilities of the film to
record them. Most importantly, if you know how to use it, it
will pretty much always give you an accurate rendering of the
subject’s tonality. And as long as the scene does not exceed
the capabilities of the film, all the other tones in the scene
will be recorded accurately in relation to the subject. All this
with one simple meter reading. Because it reads the light itself,
not the subject, it is not prone to being tricked. Whether the
subject is dark, light, or anywhere in between, an incident meter
will give you an accurate reading. This is why I am a huge fan
of this type of meter.
Now, one disclaimer: photographic film does not have the same
ability to record excessive contrast in a scene that the human
eye does. This means that even if you get an accurate reading
for the subject, if you have them say, in a very strong backlit
situation against bright sky, you will still probably get a blown
out background. This is not a fault of the meter, it’s a
weakness of film. A lower contrast film will handle excessive
scene contrast better than a high contrast film, as will film
that has had it’s contrast lowered through exposure and/or
development techniques, but there are still limits. And keep
in mind, if you were to use an unadjusted reflected light reading
in a situation like this, you would very likely get an inaccurate
exposure.
Incident meters are virtually always hand held meters that are
separate from the camera. The only exception that I am aware
of is a Hasselblad camera that can be configured with a built
in incident meter on the prism. Otherwise, we’re talking
hand-held.
Now on to the actual techniques.
METERING FOR STUDIO FLASH
In order to properly meter studio flash, it’s pretty
much a necessity to have an incident meter with flash metering
capabilities. If you don’t have one, there are calculations
you can do to determine exposure, but in my opinion that would
be like using a slide rule when you can use a calculator, and
it doesn’t leave you with much flexibility to change your
lighting during a shoot. So, on to the how to.
If you are using one light:
1. Set your meter for your film’s ISO (speed), or the ISO
you would prefer to rate your film at.
2. Set your meter for your camera’s sync speed.
3. Position your light where you would like it to be in relation
to the subject.
4. Set your meter to the “cord” function, and connect
it to the strobe via the sync cord, or plug your IR trigger into
the meter. Alternatively, you can set your meter to the “non-cord”
function and have somebody manually fire the light for you. Just
make sure they don’t block any of the light.
5. Set your light’s power level.
6. Either put the meter right in front of your subject’s
face, or stand/sit exactly where you will be placing your subject.
Accuracy in meter placement counts if you are to obtain a good
reading.
7. Point the dome of the meter at the light source. You want
to read the full amount of light striking the subject.
8. Take your reading. If you don’t have the F-stop you want,
adjust the power on your light, and take another reading. Now
you’ve got your exposure. Simple as that.
9. If you are using a reflector, once you have it positioned
as desired, you can meter the shadow side of the face to determine
the light ratio between the highlight and shadow sides of the
face. ( I realize that I am using terms like light ratio, main
light, etc. that some may understand and some not, but because
they would require another article-length post, I’m not
going to define those things here, or get into where lights should
be, what to set them at, etc. If there is enough interest, perhaps
I can discuss these things in a future post).
If you’re using multiple lights:
1. Follow all the above steps, metering your main light first.
2. Once you have your main light set, turn it off and repeat
the whole procedure with your fill light.
3. Now turn both lights on. Again, meter from the position of
the subject. This time though, point the dome of the meter at
the camera. One exception to this would be sidelighting. In that
case, pointing your meter at the main light will give you a more
accurate reading.
4. Now take your reading. This reading of both lights at the
same time will give you your total exposure. This is what you
set your camera to. In addition, the difference between the total
exposure and the fill light alone determines your light ratio.
5. If you are using a background light, turn it on, along with
the other lights, and point the dome of your meter at the camera.
This will tell you how much total light you have on the background.
You can also do this even if you’re not using a background
light but just want to know how much exposure the background
is getting.
6. If you are using a hairlight, turn it and all the other lights
on, point your meter at the hairlight, and take your reading,
from the position of the top of the subject’s head. Notice
that I had you meter the hairlight last. If you meter the other
lights with the hairlight on, you must cover the top of the meter
with your hand, to keep it from corrupting your other readings.
METERING AMBIENT LIGHT USING AN INCIDENT METER
Ok, on to the great outdoors.
If your subject is in open shade, then the area of open sky just
beyond the shade is your main light source. You will have your
subject facing this area of open sky, either directly or at an
angle. This is the metering procedure for this situation:
1. Set your meter to the “ambient” mode.
2. Set your meter for the film’s ISO speed, or the speed
you wish to rate it at.
3. Set the meter for your desired shutter speed. If you are shooting
hand-held, you must use a shutter speed number that is at least
as large (inversely) as the focal length of the lens. For example,
a 50mm lens would require a shutter speed of 1/60, an 85mm lens
would require a shutter speed of at least 1/125, etc. The exception
would be if you are using an image stabilization lens (a special
type of lens made by Canon and Nikon). With such lenses you can
use a shutter speed that is a couple steps slower than normal.
If you use a tripod, you can generally go down as slow as 1/15
if the subject is not moving, regardless what focal length lens
you are using. If the subject is fidgety, you will need at least
1/60. If the subject is moving, you’ll need 1/125 or faster,
unless you want to record the blur.
4. From the subject’s position, point the meter at your
main light source, the open sky beyond the shaded area.
5. Take your reading.
If the sun is very low in the sky, as at dawn or dusk, and you
are positioning your subject in direct sunlight:
1. Follow steps 1 through 3 above.
2. From the subject’s position, point your meter at the
sunlight. Unlike your in camera meter, your incident meter will
not be harmed by this as long as you have the dome or disc on.
3. Take your reading.
If the sunlight has fallen just below the horizon and there is
no direct sunlight anywhere. In essence, the whole sky has become
open shade. There’s not a lot of light left, but the quality
of this light can be very beautiful. If shooting under these
conditions:
1. Again follow steps 1 through 3 from above.
2. From the subject’s position, point the meter at the camera.
That’s because in this case, wherever the camera is, is
the direction your illumination is coming from.
3. Take your reading.
If your subject is in a backlit situation:
1. Again, follow 1-3 from above.
2. Stand at the subject’s position, facing the camera.
3. Use your body to shield the meter from the direct sun. If
the sun is high overhead, also shield the meter from above with
your hand.
4. Take your reading.
5. This is an aside, but realize that in this situation even
a lens shade may not prevent flare. I sometimes use a small (like
8x10) piece of cardboard to block the direct sun from the lens.
6. If you are using a reflector in this situation to try and
bring up the illumination to more closely match a light background,
then be sure you do your metering with the reflector in place.
If you are shooting indoors by window light:
1. Again, steps 1-3 from above.
2. From the subject’s position, aim your meter at the window.
3. Take your reading. This will be your exposure setting.
4. You may want to read the shadow side of the face too, to determine
if you will need a reflector, which is likely in this situation.
METERING AMBIENT LIGHT WITH YOUR IN-CAMERA METER
I will detail several methods to do this, so you should be
able to find one that suits you and your style of working.
Method 1:
Use a Kodak grey card. They are cheap, portable, and obtainable
at any decent camera store, and if used properly, will give you
the same type of consistent exposures as an incident meter.
1. If you are rating your 400 film at 200, you will need to adjust
for it in one of the following ways: a) Reset your camera’s
ISO for 200, or
b) Use +1 exposure compensation, or
c) Set your camera for one stop more exposure than your reading
indicates.
2. Have the subject hold the grey card from the same place you
will be photographing them. If it’s a small child, ask the
parent or another adult to stand in the subject’s position
and hold the grey card.
3. If your camera has a spot metering function, use it. If not,
make sure you fill the entire viewfinder with your grey card.
Take your reading, and either manually set the camera for that
exposure, or if you are using aperture priority, use exposure
lock. Since the camera is calibrated to read for middle grey,
you now have an exposure that requires no other adjustment, and
will be the same reading that an incident meter will give you.
Furthermore, your exposures will not be at the mercy of the reflectivity
of the scene or the subject.
Method 2:
1. Set your camera for +1 exposure compensation. If your camera
doesn’t have this feature, then set it for one stop more
exposure than the reading you’re about to get.
2. Meter off of the subject’s face. Unless you have spot
metering, you will need to fill the entire viewfinder with your
subject’s face in order to take the reading. Now, the reason
I had you use +1 compensation, is, as we discussed above, that
your meter is set to render your subject as 18% grey, which of
course they are not. It is commonly taught in zone system books
that Caucasian skin is zone VI, or one stop lighter than 18%
grey, which is zone V. In my experience, it actually varies,
and some folks are lighter than that, but for simplicity sake
I’m using that standard of zone VI here. If you find you’d
still like your skin tones lighter, then add ½ to one
stop. Now, here’s the rub: this simple formula I just gave
you will only work with Caucasians. If you photograph people
of other ethnicities, there is no simple formula I can give you,
because there is no one skin tone. You will either need to get
an incident meter, get a grey card, or familiarize yourself with
the tonal scale of the Zone System so that you can estimate your
own exposures.
3. With this method, if you want to rate your 400 film at 200,
you will need to either reset your camera’s ISO setting
to 200, or use +2 compensation instead of +1. If you leave your
camera set for 400 and simply use +1 compensation, you are not
overrating your film, you are simply providing the extra stop
necessary to properly expose Caucasian skin at 400.
Method 3:
This is essentially the same as method 2, but for those of
you whose cameras have spot metering functions. It’s quicker
to use on the fly, since you don’t have to worry about walking
up to your subject and filling the entire frame with their face.
If you really need to be speedy, you can set your camera for
aperture priority, just be conscious of the shutter speed so
it doesn’t get too low.
1. Set your camera for +1 exposure compensation. Again, if you
want to overrate your film by a stop, then either reset the ISO,
or use +2 compensation.
2. Set your camera for the spot metering function.
3. Get the spot portion of the viewfinder over the subject’s
face. If the lighting is not uniform, make sure you meter the
highlight side of the face.
Get your reading, lock it in, and shoot.
Happy Shooting! |
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