Photography Basics – Exposure Triangle [Part IV]

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In the Part I, II and III we dealt with basics of Exposure, how to achieve optimum exposure for various scenarios, and how to achieve optimum exposure using Filters, respectively.

Before we get into the core concepts of the exposure in detail, let us go through a very simple and easy-to-understand example.

Once you thoroughly understand the core principle behind the exposure widely known as Exposure Triangle, you will never get confused!

Exposure Triangle 

Exposure is a combination of 3 important elements, namely Aperture, Shutter Speed, and ISO. This is usually represented in a form of a Triangle like this:

Exposure-Triangle

It can also be represented with a simple equation like this:

Exposure-Simple-Equation

If we look at the Exposure Triangle or the simple equation, we understand that any change made to the Aperture, Shutter Speed or ISO results in change in Exposure. Aperture, Shutter Speed and ISO have the predefined standard values that are used by all the manufacturers.

Before getting into the details of the standard values for Aperture, Shutter Speed and ISO, let us consider a hypothetical example.

For instance, assume that the set of values for:

  • Aperture is denoted as: A1, A2, A4, A8, A16
  • Shutter Speed is denoted as: S1, S2, S4, S8, S16
  • ISO is denoted as: I1, I2, I4, I8, I16

Note that the values 1, 2, 4, 8, and 16 are powers of 2. Each value is half the previous value and double the next value. So, A4 is half the A2 and twice the A8, S8 is half the S4 and twice the S16 and so on.

Aperture-Shutter-Speed-ISO-Standard-Values-Hypothetical-Example

Understanding the doubling and halving of light is the most important aspect in understanding Exposure.

We understand a photograph is made when the Camera Sensor is exposed to the light for certain duration.

For simplicity, let us quantify the values of Aperture, Shutter Speed and ISO using amount of light they allow:

  • A1, S1, and I1 allows the complete light to pass through
  • A2, S2, and I2 allows half the light to pass through
  • A4, S4, and I4 allows quarter (1/4th) the light to pass through
  • A8, S8, and I8 allows 1/8th the light to pass through
  • A16, S16, and I16 allows 1/16th the light to pass through

Let us take it one step further to see how they add up to give us a single exposure. For a given scene, the optimum exposure needs a proper Aperture value, Shutter Speed value and ISO number like this:

Exposure-Simple-Equation-1

[Note that the actual settings for Aperture, Shutter Speed and ISO are driven by many factors like Camera meter reading, image aesthetics, composition, light, etc.]

If we happen to change any of the above values, the Optimum Exposure will change accordingly.

For instance, if we decide to change the Aperture from A2 to A4 (to increase the Depth of Field) it will effectively reduce the light by half there by underexposing the scene.

Exposure-Simple-Equation-2

To get back the optimum exposure, we could either reduce the Shutter Speed value from S8 to S4 or the ISO value from I4 to I2. The resulting equation by changing the Shutter Speed value would be:

Exposure-Simple-Equation-3

Note: We compensated for the loss of light due to Aperture change (A2 to A4) by changing the Shutter Speed value from S8 to S4, thereby balancing the equation

The resulting equation by changing the ISO value would be:

Exposure-Simple-Equation-4

Note: We compensated for the loss of light due to Aperture change (A2 to A4) by changing the ISO value from I4 to I2, thereby balancing the equation

The above example can be extended for different values of Aperture, Shutter Speed and ISO.

The idea behind the Exposure Triangle is that exposure depends on the three key factors Aperture, Shutter Speed and ISO in a way that a change in one value results in the change in overall exposure.

The question is:

Why do we want to change these three key factors and how they affect the look and feel of the final photograph?

We will discuss Aperture in the next part.

Nature Photography Simplified. Understanding Exposure, Aperture, Shutter Speed, ISO eBook. Written by Prathap.Buy Printable version of Understanding Exposure (9-Part Series) for $1.99 USD only! Contact prathapdk@gmail.com for payment details.

 

 

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3 Responses to Photography Basics – Exposure Triangle [Part IV]

  1. Roy April 8, 2014 at 10:33 am #

    Thank you for your most interesting and easy to follow articles. Have enjoyed reading and saving for future reference purposes.

    • Prathap April 9, 2014 at 12:52 am #

      Thank you! Roy

  2. Germaine January 9, 2017 at 8:16 am #

    In which can I just take Licenes

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