In today's market, digital cameras, smartphones, and point-and-shoot cameras are everywhere. With just a press of a button, these cameras/phones can capture a beautiful photo for you. There are also countless tutorials online that teach you how to "click on the screen and drag the ruler down" to take stunning silhouettes. So, what is the significance of learning exposure in this day and age?
I have pondered over this question for a long time and even had doubts at one point. However, after recently getting into film photography, I have developed a clearer perspective. As an engineer, the significance of learning exposure, in my opinion, is "being able to accurately capture the photo you desire by understanding the underlying principles."
Please note that the emphasis here is on "the photo you desire" rather than "the correct photo." After a long time, I realized that there is no perfect or correct exposure. The correct exposure is when the desired effect the author wants to convey is accurately captured.
Principles of Exposure
First, let's clarify a term: "neutral gray" (also known as 18% gray). It has two characteristics:
- It reflects 18% of light (based on statistical estimation, the reflectance of all objects in real life is approximately 18%).
- It appears to the human eye as a shade of gray with a brightness level between black and white (i.e., 50% brightness).
With these characteristics, it is evident that creating an automatic camera that reproduces the brightness of the subject as perceived by the human eye is the most universal solution. This is what smart cameras do with their automatic exposure metering.
The basic principle of exposure metering is to read and calculate the exposure value (EV)/aperture-shutter speed combination (A/S) required to capture the subject as a neutral gray.
From this, we can easily draw one conclusion and two inferences:
Conclusion: It is obvious that for a subject with the brightness of neutral gray, the parameters provided by the exposure meter are the correct shooting parameters.
Inference 1: Therefore, if we meter a black cat, the combination provided by the exposure meter is actually the aperture-shutter speed combination that would capture it as an "18% gray cat" in its eyes. Let's see the actual result (taken with a Fujifilm XT30, using automatic aperture, automatic shutter speed, and automatic ISO):
[Image: A photo of a black cat]
However, with the correct exposure metering, it looks like this (darker in color, and note that the bedsheet has returned to its normal color):
[Image: A photo of a black cat with correct exposure]
Inference 2: Similarly, if we meter a white duck in a snowy field, the combination provided by the exposure meter is actually the aperture-shutter speed combination that would capture it as an "18% gray duck" in its eyes. Here's the actual photo (assuming it is a pure white duck):
[Image: A photo of a white duck in a snowy field]
But to the naked eye, it actually appears closer to this shade of white:
[Image: A photo of a white duck]
Therefore, for "scenes with relatively simple content," just follow these principles:
- Find a subject with 50% brightness or close to neutral gray brightness and use the meter reading directly.
So, what are some objects that are close to neutral gray?
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Grass, especially freshly cut grass (not dark green, special green, or yellowish grass).
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Most light green tree leaves or plant leaves.
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Some tree trunks.
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Old or repaired asphalt roads and concrete.
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Wood that has been left untreated and not oiled for a long time.
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Red or brown bricks, including cement walls.
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Dry leaves.
Of course, if none of the above can be found, you can meter your own hand. -
Meter the subject directly, following the "add exposure for white, subtract exposure for black" principle. In other words, "if it is brighter than neutral gray, increase the exposure (increase compensation, change the combination, etc.); if it is darker than neutral gray, decrease the exposure."
What about scenes with more complex content? Stay tuned for the next article on "Zone Exposure."