Easy Basic Photography
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Digital Camera Metering and Metering Modes
A key element in taking pictures is obtaining a correct exposure reading. In other words you don't want your picture to
be too dark or too light. All digital cameras are equipped with built in light meters. The camera's light meter reads the
luminance (brightness or radiance) of light being reflected from a scene or subject. Please note that camera light meters
are only reading the radiance or brightness of the light and not the color of the light.
In order to reproduce that same luminance in an image, the camera's metering system is programmed to assume that
an average scene is reflecting about 18% of the light in it. Specifically, reflected light from a middle tone of gray (halfway
between black and white) is used as the standard. So when you manually set your camera's aperture and shutter
speed to obtain the correct exposure value, they are being set so that the overall reflected light from the scene will be
recorded and reproduced in the image somewhere in a mid-tone range. The same thing happens when the camera is
used in the automatic exposure mode.
Another thing you should know about light meters...if you are taking a picture and something white like snow dominates
the scene, the camera meter will assume it is too bright and set an exposure value to try and make the snow darker or in
a mid tone range. The whole picture will be underexposed. The reverse is true if you are photographing something that
is predominantly dark or black. The meter will assume it is too dark and suggest an exposure value to lighten it so that it
records more in the mid tone range. In those type cases, you will have to use your camera's exposure compensation
feature or manually adjust the aperture and shutter speed.
Digital camera light meters are a great tool but all lighting situations are not the same and certain metering modes will
work better under certain lighting situations.
The following is a summary of the most common digital camera metering modes. Digital SLR camera users are able to
manually switch between the metering modes listed below. Compact camera users may have one or more of the
following modes in their cameras, but might not be able to manually change between them.
Center Weighted Average
This metering mode assumes that the main subject is located somewhere in the middle of the frame. When calculating a
proper exposure, the camera meter will concentrate on, and give the most weight to a 60-80% area of the middle of the
frame. The light readings for the remaining
areas around the frame are also taken into
account and averaged in with the rest of the
scene, but are not given as much weight.
So the center weighted average mode will be
less influenced by very bright or very dark
areas around the edges of the viewfinder.
The pictures to the right show an approximate
area for a center weighted metering image
and the resulting image.
The center weighted average mode is
included in just about every compact and Digital SLR camera and works well in most average picture taking situations.
That is provided there are no extreme contrasts of light in the main area that is being metered.
Evaluative or Matrix Metering Mode
The evaluative or matrix metering mode measures light in multiple areas of the entire frame. (it is also know as pattern
metering) These areas are called zones and are analyzed individually. The grid below shows an example of how a
sixteen zone focusing area might look. The five very small rectangles across the middle are the focusing points. The
number of zones in a camera might be fewer than sixteen or sometimes a great deal more. The exact method of
calculating the exposure value from the readings in these individual zones can vary from camera to camera.
Some of the factors taken into account when the exposure is being calculated are the areas at the auto focus points,
the distance and position of subject. In or out of focus areas as well as background and foreground brightness also
considered in the exposure calculation. The light readings taken from the scene are averaged out and are also
compared to thousands of images stored in the camera's database of typical pictures. The camera will then set an
exposure that is typical of the scene being taken. That method works well for a typical scene like the one above. Yes,
you could say there is some guessing in this equation, but the evaluative mode works well in most situations and is more
accurate than the center weighted mode. The only problem is that you don't always know what areas in the frame are
carrying the most weight in the calculations, so you might get unexpected results every now and then.
Spot Metering or Partial Metering
The light meter will take a reading from a small area or spot of the frame when you use the spot metering mode. This
area might be 1-5% of the viewfinder area and it is usually in the center of the frame, however, some advanced cameras
might offer multiple spot metering areas within the frame. Partial metering works basically the same as spot metering but
will cover a slightly larger area or spot in the frame.
The photo of the statue on the left was originally taken using
the center weighted mode. The statue is too dark with not
enough detail. The spot in the picture on the right shows the
approximate area that might be used in the spot metering
mode. The picture on the right shows results after spot
metering. Please note that in this case the exposure value
had to be adjusted to EV-1 because the metered area was
very dark and without the EV-1 adjustment, the overall picture
wouldhave been too light. Spot metering consists of taking a
light reading from a very small area in the viewfinder while
basically ignoring the light readings from the remainder of the
frame. Spot metering is good to use in back lit situations to
keep the subject from being underexposed. Spot metering
will give a more accurate reading for a particular subject in an image, however, there is always the possibility that the
other areas in the frame will be overexposed or underexposed. That is, if the overall lighting in the frame is not even.
So spot metering is best used when the main subject needs to be properly exposed more than anything else in the
frame.
A key element in taking pictures is obtaining a correct exposure reading. In other words you don't want your picture to
be too dark or too light. All digital cameras are equipped with built in light meters. The camera's light meter reads the
luminance (brightness or radiance) of light being reflected from a scene or subject. Please note that camera light meters
are only reading the radiance or brightness of the light and not the color of the light.
In order to reproduce that same luminance in an image, the camera's metering system is programmed to assume that
an average scene is reflecting about 18% of the light in it. Specifically, reflected light from a middle tone of gray (halfway
between black and white) is used as the standard. So when you manually set your camera's aperture and shutter
speed to obtain the correct exposure value, they are being set so that the overall reflected light from the scene will be
recorded and reproduced in the image somewhere in a mid-tone range. The same thing happens when the camera is
used in the automatic exposure mode.
Another thing you should know about light meters...if you are taking a picture and something white like snow dominates
the scene, the camera meter will assume it is too bright and set an exposure value to try and make the snow darker or in
a mid tone range. The whole picture will be underexposed. The reverse is true if you are photographing something that
is predominantly dark or black. The meter will assume it is too dark and suggest an exposure value to lighten it so that it
records more in the mid tone range. In those type cases, you will have to use your camera's exposure compensation
feature or manually adjust the aperture and shutter speed.
Digital camera light meters are a great tool but all lighting situations are not the same and certain metering modes will
work better under certain lighting situations.
The following is a summary of the most common digital camera metering modes. Digital SLR camera users are able to
manually switch between the metering modes listed below. Compact camera users may have one or more of the
following modes in their cameras, but might not be able to manually change between them.
Center Weighted Average
This metering mode assumes that the main subject is located somewhere in the middle of the frame. When calculating a
proper exposure, the camera meter will concentrate on, and give the most weight to a 60-80% area of the middle of the
frame. The light readings for the remaining
areas around the frame are also taken into
account and averaged in with the rest of the
scene, but are not given as much weight.
So the center weighted average mode will be
less influenced by very bright or very dark
areas around the edges of the viewfinder.
The pictures to the right show an approximate
area for a center weighted metering image
and the resulting image.
The center weighted average mode is
included in just about every compact and Digital SLR camera and works well in most average picture taking situations.
That is provided there are no extreme contrasts of light in the main area that is being metered.
Evaluative or Matrix Metering Mode
The evaluative or matrix metering mode measures light in multiple areas of the entire frame. (it is also know as pattern
metering) These areas are called zones and are analyzed individually. The grid below shows an example of how a
sixteen zone focusing area might look. The five very small rectangles across the middle are the focusing points. The
number of zones in a camera might be fewer than sixteen or sometimes a great deal more. The exact method of
calculating the exposure value from the readings in these individual zones can vary from camera to camera.
Some of the factors taken into account when the exposure is being calculated are the areas at the auto focus points,
the distance and position of subject. In or out of focus areas as well as background and foreground brightness also
considered in the exposure calculation. The light readings taken from the scene are averaged out and are also
compared to thousands of images stored in the camera's database of typical pictures. The camera will then set an
exposure that is typical of the scene being taken. That method works well for a typical scene like the one above. Yes,
you could say there is some guessing in this equation, but the evaluative mode works well in most situations and is more
accurate than the center weighted mode. The only problem is that you don't always know what areas in the frame are
carrying the most weight in the calculations, so you might get unexpected results every now and then.
Spot Metering or Partial Metering
The light meter will take a reading from a small area or spot of the frame when you use the spot metering mode. This
area might be 1-5% of the viewfinder area and it is usually in the center of the frame, however, some advanced cameras
might offer multiple spot metering areas within the frame. Partial metering works basically the same as spot metering but
will cover a slightly larger area or spot in the frame.
The photo of the statue on the left was originally taken using
the center weighted mode. The statue is too dark with not
enough detail. The spot in the picture on the right shows the
approximate area that might be used in the spot metering
mode. The picture on the right shows results after spot
metering. Please note that in this case the exposure value
had to be adjusted to EV-1 because the metered area was
very dark and without the EV-1 adjustment, the overall picture
wouldhave been too light. Spot metering consists of taking a
light reading from a very small area in the viewfinder while
basically ignoring the light readings from the remainder of the
frame. Spot metering is good to use in back lit situations to
keep the subject from being underexposed. Spot metering
will give a more accurate reading for a particular subject in an image, however, there is always the possibility that the
other areas in the frame will be overexposed or underexposed. That is, if the overall lighting in the frame is not even.
So spot metering is best used when the main subject needs to be properly exposed more than anything else in the
frame.
