(EP) Creating Correct Exposures Lesson
Creating Correct Exposures
The Limits!
Now that you have a thorough understanding of the exposure triangle and how the elements of ISO, aperture, and shutter speed interact with one another, it’s time to explore your camera meter and its limitations. Those automatic settings on cameras are great – until they aren’t. It doesn’t take long to encounter a situation where they just don’t seem to work correctly. Even when you start setting your exposures manually there are times with the meter is incorrect. Understanding metering is the next step in taking full control of your photography and learning to bring your visions to life.
The Right Light
In the early days of photography, photographers relied on experience to determine the best settings for exposure. Technology has evolved greatly since then, and most cameras now have a built-in light meter and often an automatic exposure system as well. Those automatic settings on cameras are great – until they aren’t. It doesn’t take long to encounter a situation where they just don’t seem to work correctly. Even when you start setting your exposures manually there are times with the meter is incorrect. Understanding metering is the next step in taking full control of your photography and learning to bring your visions to life.
Ideal Light
Photo materials, be they film, silver gelatin paper, or digital sensors react predictably to light within a certain range of exposure. A correct exposure yields the greatest amount of detail possible in both light and shadow areas along with the greatest tonal range. There are many reasons a photographer would choose to allow more or less light for the exposure than the meter indicates. A light meter does not know what the photographer hopes to communicate through their image. A photograph that is intended to convey mood might require a different exposure than one that hopes to record the greatest amount of detail. So you can see it’s definitely useful to understand the exposure triangle and manual settings.
How to Meter a Photograph
Measuring Light
Light metering systems
The ability to consciously adapt exposure to the intended effect is one of the most fundamental skills of a photographer. While light metering systems and camera automation continue to advance, a light meter has no way of knowing what a photographer wants the image to convey. A photograph intended to capture the maximum amount of technical detail may need a different level of exposure than one meant to convey the mood of a place, even in the same location and with the same amount of light present. It is all a question of intent, and until cameras can read photographers' minds, it is definitely useful to understand exposure thoroughly.
Traditional silver-gelatin emulsion film reacts to light by turning darker the more it is exposed. This relationship between exposure and the resulting tone depends on a lot of factors, including the sensitivity of the material and the development process, but in the broadest terms within a "normal" range is predictable and linear. This means that adding exposure will increase the density of the silver deposit on the film by a predictable amount. However, this is true within a certain range of light levels, called the film's exposure range or latitude. At very low light levels, the film will not react at all, while above it all the available silver compounds in the film will be converted to metallic silver and further exposure will not result in any further change. It is important for a practicing photographer to know these limits.
Conventionally, exposure is expressed in "stops". Each stop is equivalent to doubling the amount of light of the stop below it and halving that of the one above. Most cameras control the amount of light entering using an aperture, which controls the amount of light entering, and a shutter, which controls the amount of time for which the light is allowed to enter the camera. Each of these devices is calibrated in stops, to make it easy to adjust exposures quickly and efficiently.
Aspects affecting Exposure
Once the ISO is set, either by film selection or digital camera setting, the exposure is set by the remainder of the exposure triangle: aperture and shutter speed. Both of these are often expressed in terms of stops. Each step in the progression is double the amount of light of the stop below it. This allows for quick and easy compensation between the two settings.
Exposures are usually given as a combination of aperture and shutter speed. For example, on a sunny day with an ISO of 200, a typical exposure might be 1/200s with an aperture of f/16. Since stops in both shutter speed and aperture are equivalent in the amount of light they allow in, and exposure of 1/400s and f/8 would allow the same amount of light to reach the sensor. A faster shutter speed will freeze faster motion but there would be a shallower depth of field.
It is also possible to change the exposure from what the meter says is “correct”. The same scene could be underexposed (1/200s with an aperture of f/22 would be one-stop underexposed) to emphasize detail in the light areas of the scene while compressing its shadows. Overexposure does the opposite – dark shadows have greater detail than normal and light areas will lose information.
Regardless of the intent of the image, it is worth remembering that while modern light meters and camera exposure systems are great at setting "correct" exposures, equipment manufacturers calibrate these for average conditions. This means that a scene is metered and the settings calibrated so that an overall medium grey tone is achieved at a minimum. This means that scenes of extreme color or lighting, something mostly black or white, is not metered correctly by the automatic settings. Taking a picture in a coal mine or a sun-blasted snowy slope is not "typical" conditions. In order to achieve predictable results, a knowledgeable photographer will adjust the exposure in each instance. In the examples above, since coal is black, it will fool the light meter into "thinking" that there is less light in the scene than there really is, resulting in overexposure. Muddy snow scenes are often the result of a photographer letting a camera do its own thing, where a large amount of light reflected from the snow tells the system that the scene is far more brightly lit than it is in reality. Again, there is no substitute for conscious choice.
Take a moment to investigate what happens in extreme lighting situations. Below are two examples of when your camera meter will not create a well-balanced exposure if you follow its feedback.
IMAGES CREATED BY GAVS