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What is Exposure? (The Balance of Light)

  • emrahuelke
  • 2 days ago
  • 2 min read

What does "Exposure" mean? And what are the conditions for a "Correct Exposure"?

In this post, I will explain these essential concepts. Technically, taking a photo means exposing a sensor or film to light. To create an image, light must fall onto the sensor for a specific amount of time through mechanisms like aperture and shutter. Photography is the art of controlling how and for how long this light affects the sensor.


The Exposure Triangle

Technically, exposure is the amount of light that reaches the sensor. Simply put, it determines whether your photo looks too bright, too dark, or just right. Exposure is determined by three main elements:

  1. Aperture: The opening of the lens ($f$-stop).

  2. Shutter Speed: The duration the shutter stays open.

  3. ISO: The sensitivity of the sensor to light.


The Water Cup Metaphor (Updated)

Let’s look at our favorite analogy again:

  • Aperture is the tap: It controls how much water (light) flows.

  • Shutter Speed is the time: How long you keep the tap open.

  • ISO is the cup: Imagine it as the capacity or sensitivity of the cup. If the cup is very sensitive (High ISO), it fills up much faster, but it might get "noisy" (digital grain).


The Law of Reciprocity (Eşdeğerlilik Yasası)

These three elements—Aperture, Shutter Speed, and ISO—always work together. This relationship is called the Law of Reciprocity.


It means there is more than one way to get the "correct exposure." For example:

  • If you close your aperture by 1 stop (less light), you must slow down your shutter speed by 1 stop (more time) to keep the same exposure.

  • Similarly, if you increase your ISO by 1 stop, you need to either use a faster shutter speed or a narrower aperture to balance the light.


Same Light, Different Feeling

According to the Law of Reciprocity, the "brightness" of the photo remains the same in different combinations, but the artistic result changes:

  • As the Aperture gets wider (smaller f-number), the depth of field decreases (blurry background).

  • As the Shutter Speed gets slower, the motion blur increases (movement effect).

Understanding this balance is the key to moving from "taking a picture" to "creating a photograph."

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