ISO, aperture, shutter speed

The Holy Trinity of photography

In this lesson we will examine the three key pillars of photography.

Understanding ISO, aperture and shutter speed serves as the foundation of all photographic endeavors.

These three pillars control how bright or dark your photo will be, and they also have a big impact on the character of your picture.

For example, with a slow shutter speed the camera might move, and your photo will come out blurry. (…which might just be intentional, but let’s not rush ahead! Let’s start at the beginning—scroll down!)

This image is an illustration from the interactive block you will find below:

ISO érzékenység

1. Let’s start with ISO speed

Let’s talk about the first item of the ISO, aperture and shutter speed trinity!

ISO speed adjusts the sensitivity of your digital sensor. In low light you increase the ISO value. When there is lots of light, you decrease it.


Check out a few basic settings in the interactive block below!

Attention! This is an interactive block. Follow the instructions and the icons to see where to click! 🙂

Uh-oh! Interactive sliders may not work perfectly on all touch screen devices. If you are having problems, please try again with a mouse! 🙂

What to watch out for:

  • The higher your ISO sensitivity is, the noisier/lower quality your photo will become.
  • ISO speed and sensitivity are directly proportional: higher ISO speed means higher sensitivity.
  • ISO speed always doubles as you go up, just as sensitivity does.
  • For example, with an ISO of 200 your shutter speed will be half of what you’d need with ISO 100.

By doing this you have changed the EXPOSURE VALUE by 1.

(e.g., decreasing ISO from 400 to 200 you reduce your ISO speed by 1 EV)


Whenever you can, reduce ISO sensitivity to improve the quality of your photo!

However, it’s not always possible; sometimes you have to increase your ISO to avoid using a slow shutter speed that might result in a blurred photo.

ISO speed should be the first thing you adjust when taking a photo. Just look up to see how much light you have and set your ISO on the camera accordingly.

Right, let’s move on!

2. Shutter speed

Shutter speed (also called exposure time) refers to the length of time your camera’s light-sensitive sensor is exposed to light.

Two simple examples:


Attention! This is an interactive block. Follow the instructions and the icons to see where to click! 🙂


  • Attention! This scale is inversely proportional.
  • The higher the value, the FASTER your shutter speed will be!
  • Similar to ISO speed, shutter speed values are doubled or halved too (OK, with a bit of rounding :-)), just as the length of exposure time is doubled or halved.
  • For example, if you set your shutter speed to 1/2, exposure time will be half a second long. If you reset it to 1/4, your exposure time will be half as long.

By doing this you have changed the EXPOSURE VALUE by 1.

(every doubling or halving of the shutter speed will do this >> from 1/30 to 1/60, etc.)

All right, of ISO, aperture and shutter speed, we only have aperture left. Scroll down!

3. Aperture

The third, super-important value to set when taking a photo is APERTURE. This mechanism of metal plates inside your camera lens is able to control the quantity of light that passes through it by opening or closing.

a blende

Wide aperture lets in lots of light, while a narrow one lets in less. 

Attention! This is an interactive block. Follow the instructions and the icons to see where to click! 🙂


Okay, pay attention please! This is not as simple as ISO sensitivity.


  • Similar to shutter speed, the aperture scale is inversely proportional >> when the VALUE IS SET HIGH, it lets in LESS LIGHT (you have a narrow aperture).
  • The numbers double by every second value, e.g., 2.8, then 4, then 5.6 (which is double 2.8).
  • Despite the above, the amount of light passing through the lens is halved AT EACH VALUE (or doubled, if you go in the other direction), e.g., when you change your aperture from 2.8 to 4, you HALF the amount of light that enters the lens.
  • These values aren’t very important on their own, but you will have to be able to read the current aperture settings on your camera.
  • When there is too much light, you narrow the aperture. When there is not enough, you set a wider one.

When you go one stop up or down the aperture scale, you change the EXPOSURE VALUE by 1.


Important! Resetting any of your ISO, aperture or shutter speed values by one unit is universally called changing your exposure value by 1.

But why all these weird numbers?!

Aperture values are numbered this way because the amount of light is not measured on a linear scale. Instead, it changes on an exponential/logarithmic scaledecreasing inversely proportional to the square of the distance.

So… now you know! 😀

You have reached the end of this lesson. Enjoy exploring our other content too! You can always pick the next lesson from the  top menu!

Here is a little interactive 3D aperture fun for you

About the author:

Bence Gyulai is a photographer and professional photography teacher. Grand Prize-winning photographer of the Hungarian Academy of Sciences, regular invited speaker at photography events, founder and host of  More info & images >>

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