The Exposure Triangle

Snow Goose at Bosque

The exposure Triangle, no it's not a basketball practice ran by Phil Jackson at a nudist camp, is the term that describes the three ways we control the amount of light available to the sensor in the camera. Once we understand how each of these three camera settings work we can adjust them based on our shooting needs to get the shot we want and maintain a proper exposure. So lets break down each side of that triangle first.


TIME(Shutter Speed)

This is the easiest one to understand. It's the length of time the shutter is open. It's not a hard concept to understand that the longer you leave the shutter open the more light will reach the sensor. It's no different than the faucet in your bathtub. The longer you leave it on the more full the tub gets.

Where time comes in handy in photography is when we are shooting action such as sports or wildlife. If we want to freeze the action we want to use a very fast shutter speed. If we want to allow for some blur to impart a sense of motion then we want to use a slower shutter speed and pan with the moving subject. I'll get to this more in a moment.


F/ STOP

F/Stop's seem to be the most confusing part of the exposure triangle. I think that has to do with the fact that the smaller the number the bigger the opening and thus the larger the amount of light being allowed through to the sensor. The reason it works this way is because f/stops are derived from a mathematical expression of the focal length divided by the width of the opening. You can blame this on telescope makers. Maybe this is the real reason the catholic church persecuted Galileo.

Where f/stops come in handy is in story telling. I wrote a post here on Steemit already about telling the three stories of this thing, this thing in this place, and this place. I'll link it at the end of this post. I'll also give a quick demo on how to do those things with the exposure triangle in just a moment.


ISO

In the days of film you set your ISO at the counter of the drugstore when you picked out which film you were buying. Today you set your ISO with a dial, or a menu setting on a cheap camera. On digital camera's ISO is increased or decreased by the camera increasing or decreasing the gain on the signal coming from the sensor.

Think of it sort of like you turning up the volume on your car stereo. The better your stereo the higher you can turn the volume but at some point they all start to sound horrible. Cameras work the same way. The better their noise to signal ratio the higher you can push the ISO before the image becomes unusable. Most cameras are good up to about 3200 ISO. This is one area where true professional camera separate themselves and are often able to get good images as high as 51200.


Adjusting the Exposure Triangle for Time

Let's take a look at a simple version of an exposure chart:

Now lets assume we'd get a correct exposure at f/5.6, 1/250, and 200 ISO. The problem we have though is we are out at Bosque today because our granola eating buddy dragged us out there. Despite it being cold and wet we're able to think just long enough to realize we need a fast shutter speed to photograph the birds as they move around. Then we move the shutter speed from 1/250 up to 1/1000 which means we've given up two stops of light that we must now make up somewhere else. We can get one of those stops back by cranking the ISO up to 400 and another by making the f/stop f/4 instead of f/5.6. I often do this little of both strategy rather than get all of it from just one column.

Now lets say we wanted the opposite effect because we are at an auto race and want to get a little blur in the shot while we pan to follow the cars. We'd drop the exposure down to 1/30 and then drop the ISO to 100 and make the f/stop f/8. Thus adding two stops to the shutter speed and taking one away from both the ISO and the f/stop.


Story Telling with F/stops

Again, I've already written an in depth post that I'll length below but I'll give a quick idea of how to use the exposure triangle to do what that post suggests. That way as you read it hopefully everything clicks.

This Thing – You want a narrow depth of field so you will need a faster shutter speed and lower ISO number so you can use a lower f/stop number

This Thing in this place – Think of this as the mamma bear of settings, everything in the middle

This place – you'll want a lot of depth of field so you need a high f/stop number. That means you'll need a higher ISO number and a slower shutter speed. Don't go to high on that ISO though or noise might ruin your shot. It's better to use a slower shutter speed and a tripod.


Concluding Thoughts

So there you have it, my fully abridged, barely comprehensible explanation of the exposure triangle. If you don't have it down don't worry. Only slightly less has been written about the exposure triangle than about some guy that walked on water and I'm still not sure I understand any of that stuff. Tomorrow is Saturday so that means it's Photography news weekly round up. I'll see you tomorrow when I tell you about all the new stuff we can't afford.


Understanding Depth of Field: Storytelling
https://steemit.com/photography/@randystiefer/understanding-depth-of-field-storytelling