The Exposure Triangle – Photography Basics

Photography Bascis - Exposure TriangleWith our law and rules finished, let’s jump into how to make a photo.

The Exposure Triangle

First, there is The Exposure Triangle. It balances all things. Makes things right in the Universe. Or maybe it is just a handy metaphor.

To be honest, the Exposure Triangle, to me, is better explained as two Teeter-Totters, which isn’t nearly as sexy as a triangle. What the Exposure Triangle is trying to tell you, is there are three things which have an impact on proper exposure of an image on film or on a camera sensor:

  • Shutter Speed
  • Aperture
  • ISO

We’ll be going over each of those in more detail in the following days.

Shutter Speed

Photography Bascis - Exposure Triangle
Tree Amongst Rock Formations, Bryce Canyon National Park, Utah, USA, North America

Essentially, this is how fast your camera blinks. Remember the days of film and how you were never, ever, ever, ever supposed to open the back of the camera while the film was loaded? That’s because film reacts to light and if you don’t control how much light hits it, it freaks out and exposes EVERYTHING. Much cursing typically ensued.

So the shutter does the blinking of the camera (from closed to open and back to closed). Everything is dark inside the camera and then “BLINK”, the shutter lets in how ever much light it is told to. More on this tomorrow.


The Aperture is analogous to the pupil in your eye. It’s a hole that lets in light and can be changed in most cameras and even some smartphones.

Let’s use an analogy. It’s pitch-black inside this room the is 20′ x 20′ and you are standing in the center. Outside the room is daylight. Are you with me?

Next to you is a 40 ton, 8′ wide wrecking ball. You’ve been working out and are feeling destructive so you swing the ball forward and BAM! 8′ wide hole in your wall. How much light do you think is coming in right now? Tons.

Now back up and let’s do this again. Instead of a wrecking ball, let’s use a 1” wide drill bit on that wall. POP! Hole is in and, if you are standing back 10′, how brightly lit is the room now?

Can you see now how Aperture affects how much light comes into the room? More on how the aperture does other cool stuff on Friday.


Photography Bascis - Exposure Triangle
The ferry boat Kittitas approaches a dock in a high key photograph

People often ask what ISO stands for; International Standards Organization. I get blank looks after that answer or “Oh, ok” looks followed by, “Huh?”. Wikipedia has thousands of words on ISO as it relates to photography, but in short, we’re talking about sensitivity here.

It’s the exact same sensitivity as if I punch you. If you’re a body builder, you’re not that sensitive to a punch. But if you’re….oh jeeze, now I need to come up with an example where I punch something sensitive…a cute, fluffy bunny. Sorry bunnies. Chances are, with the same punch the bunnies would yelp and jump a mile because of the guns I’m packing on this 6’1” frame. (sorry, obscure, and sometimes old, pop culture internet references may come up this month)

Better yet, let’s go back to the wrecking ball analogy. You’re in the pitch black room before the ball smashes an 8′ hole in the wall. If you’ve been in the pitch black room for an hour, your eyes are far more sensitive to light, aren’t they? Your pupils are open wide, trying to gather as much light as they can.

BAM! The ball smashes a hole and ARGGHHH!! You sensitive eyes don’t like all that light.

Same scenario but this time, before the ball strikes, we’ve been holding a flashlight pointed into your eyes for 10 minutes. By ‘we’ I mean me and the bunny you made me punch. Your eyes are now constricted and not so sensitive, are they?

BAM! Hole in the wall and you think, “Eh, not so bright”. Your eyes were less sensitive.

ISO will be covered on next Monday.

Got all that? Shutter speed = how long light hits your camera sensor. Aperture = how wide is the hole letting in light. ISO = how sensitive the sensor is to light.


Here’s where the triangle comes in. Visualize it like this:

Exposure TriangleExcept for the bunny, it’s a nice balanced triangle. However, the moment one of those corners changes, let’s say you change the ISO from 100 to 400, then the triangle gets all fuddled up and is not in balance any more.

If one, or both, of the other variables aren’t moved as well, the bunny picture won’t come out properly exposed. And by properly exposed I’m talking about an ideal here. After you learn the rules through these 43 days, you’re welcome to break them as mentioned yesterday. But until then, we’re shooting for properly exposed images.


Another way to think of it is:

Exposure Triangle

With the Exposure Teeter Totters Of Doom, if ISO wants to move up or down, one of his buddies (or possibly both) needs to go in the opposite direction to make all things even. This is all in regards to the amount of light hitting the camera sensor. Any of the three could be in the middle and if it is changed, one or both of the other two needs to change to keep exposure proper and level.

Exposure Triangle
Silhouette of mountain with trees at sunset – East Africa – Tanzania

Currently a lot of smartphones, action cameras and drones have a fixed Aperture, so you only have two settings to play with; ISO and Shutter Speed. Most DSLRs and point-and-shoot cameras can adjust all three.

That’s it!! That’s the Exposure Triangle. It’s not a huge mystery, really. It is simply an attempt to keep all things in balance for a proper exposure. Those three things, explained more fully over the coming days, are what determine a proper exposure. ISO, Shutter Speed and Aperture.

Experiment With It

Here are a few practical experiments you can try at home to help the concepts take form:

Tomorrow we will cover How Your Camera Works.

Questions?  Pop ’em like Pez in the comments section below. or email me at

Photography Basics – A 43 Day Adventure, and its companion 40 Photography Experiments, are series written by professional photographer Peter West Carey. The series are designed to unravel the mysteries of photography, helping you can take better pictures. Subscribe here to receive all the updates and bonus material. Your comments are always welcome.

Photo ToursIf you enjoy the series, consider learning photography first-hand on a professionally led international photo tour in Nepal or Bhutan. More information can be found at Far Horizon Photo Tours

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