Exposure

ISO 200 | 0.5 seconds | f/29

ISO 200 | 0.5 seconds | f/29

Every single photograph in this example has the same tonal balance.

Meaning it is not really any lighter nor darker than the others, aside from the variable of shooting in natural light.

The ISO remains constant at 200, while it's the Shutter-Speed and the Aperture values which change, visually altering the water motion in the photographs.


Photography is about capturing light and creating an image with a good, balanced exposure, where we have detail in areas of dark shadows and bright highlights.

Cameras come with a built-in light-meter that measures the amount of light being REFLECTED off a subject. This type of light-meter sees a world not in color, but in tones of gray.

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A reflected light-meter searches for the halfway-point between full-black and full-white, something called 18% gray.

Based on the light being measured, the meter will then create a formula value for the ISO, Shutter-Speed and Aperture. When we take the picture, we should have a good tonal balance.


The downside to a reflected-meter is when there's a very bright scene like snow, a sandy beach, a lamp or the sun. The meter measures all this reflected light and will adjust our exposure downwards  to compensate.

Our beautiful white snow is now gray and people against a bright sky, are in dark silhouette.

Likewise, if we're photographing a black surface, such as a cat or a large dark statue, they also will not be represented accurately.

The exposure will be shifted upwards  to a dark shade of gray, over-exposing our image.

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I was at the Keene Pumpkin Festival and took 2 photographs to show what I mean..

With one, I just pointed the camera and took the photograph in full-automatic mode. Since the bright street lights were part of the metering equation, the camera took a very dark, under-exposed photograph for me.

In the second photograph, I went full manual and pointed the camera downward.

With the reflected light-meter now concentrating solely  on the pumpkins, I set the ISO, Shutter-Speed and Aperture values to what my meter indicated were good values, and took the photograph. (I can also use a camera's "Exposure-Lock"  feature to accomplish this.)

By avoiding those bright lights, we can now see everything much more clearly.

The same solution can be applied to bright daylight.

Turn the camera away  from the sun, get a meter reading and adjust the settings, then turn around, compose and take the picture. Some cameras allow us to over-expose and under-expose things at will. 

Despite its faults, a reflected light meter does a very good job overall.

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This is how a typical reflected light-meter display might look in a digital SLR camera (DSLR). 

The meter uses individual lighted-bars to display the amount of light being detected at that moment.

If the only bar being illuminated is right in the center ("0"), then according to the meter we have a good balanced  exposure.

Neither too dark, nor too light. 

If I take a meter reading and I have more lighted bars in the positive (+) end of the meter, I am in danger of being over-exposed. The solution is to adjust the last property value I set, so I can bring my meter into balance at 0.

Lighted bars in the negative territory (-), indicate I am in danger of being under-exposed.

I have too little light getting through and the solution is to somehow allow more light in. In that case, adjusting the ISO to increase the sensitivity will usually resolve the problem.

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An incident  light-meter is a hand-held device which measures the amount of AMBIENT light falling on our subject. 

Unlike reflected meters, an incident meter sees a world in color.

This type of meter is not fooled by bright light or a black cat. Blacks are rendered as being black, and white snow is rendered white.

We can be photographing something right in front of us, or a mountain range miles away. As long as we are ALL in the same light, the exposure will be accurate.

Just set an ISO value and press a button. The meter will come up with a formula for what the Shutter-Speed and Aperture values should be.

Up and Down buttons on the meter allow us to cycle through all the different property value options available. I simply decide which formula will best fit the situation, then set my camera accordingly and take the photograph. 

Such meters are far more accurate than the reflected ones, and plug-in accessories are available to turn a mobile device into an incident meter.

If things look good, take a picture and judge the results.

A digital camera's LCD display allows for instant feedback of our photos, nothing more.

NEVER trust it to determine if the exposure is good or not.


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Instead, if your camera (or the app) has a Histogram display, use that.

In a histogram, the brightness value of each pixel is measured, organized and stacked one-upon-another. The graph it creates goes horizontally across the bottom, from left (black) to right (white) and covers the entire tonal range in-between.

Pixels are also stacked vertically, and the more pixels there are at any given point, the taller the graph. Our aim is for a balanced exposure, something resembling a mountain range, where the pixels are concentrated in the middle of the graph.

Having a graph pegged too-far left (too dark) or too-far right (too bright), will show where the problems areas are and that a correction needs to be made.

The moment of capture is a time of magic, when our creative and technical sides come into play. We imagine a photograph first. Then we use our knowledge of ISO, Shutter-Speed and Aperture to bring that image to reality in the form of a final photograph.

Remember, when we take a picture, there is a very small chance that the camera's auto mode will deliver the exact photograph we are imagining.

It probably has a good tonal balance to it, but is there a better Shutter-Speed  we could be using? Do we want to blur the background with Aperture  so our friends stand out more in the photograph.

Once we determine what settings deliver a good exposure, we can fine-tune things.

As I've repeatedly said, I always set the ISO first. 

This is a throwback to my early days when we'd put a roll of film in the camera and set a dial to whatever the roll's ISO was.

It worked then and it applies to digital. ISO is the foundation on which our exposure house is being built.

Next, I set the next property (Shutter-Speed or Aperture) to whatever value will provide the biggest impact for my image. 

The remaining property value is set to whatever will bring my light-meter into balance at 0. It will also be the first one to change if I need to make any changes.

The Exposure Triangle

"The world just does not fit conveniently into the format of a 35mm camera."

W. Eugene Smith

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