1. Photo Tips - The Exposure Triangle

1. Photo Tips - The Exposure Triangle

16th of May, 2020

1. Photo Tips - The Exposure Triangle

The what? Yep, the exposure triangle. This is the most basic element to taking a photo and the first part in understanding how to take the perfect shot, in any condition, and getting off auto mode.

So, what is it? Exposure is just the amount of light reaching your camera’s sensor. It’s being ‘exposed’ to light. The Exposure Triangle is simply balancing three factors to get a correctly exposed image. These factors are Aperture, Shutter Speed, and ISO.

First, Aperture.

Your aperture can be equated to the iris of your eye. If it’s bright your iris contracts to limit the amount of light that enters your eye. Conversely, if it’s dark your iris expands to let more light in.  So, aperture limits the amount of light that enters the lens and hits your sensor. 

On your camera lens you’ve no doubt seen an ‘F’ number or seen this selection on one of the dials on the camera body. You might even have ‘A’ mode on your own camera, which is aperture priority. More on that at the end of this blog. 

The ‘F’ number just tells us how wide the aperture is on the lens before you take a photo. The lower the number the wider your aperture. The higher the number the smaller the aperture. Try it on your camera. Move the aperture dial and see what happens to the brightness of the image in the view finder or screen. 

You might here photographers talking about their lens being “wide open”. Just means it’s the widest aperture, or smallest 'F' number they have on that lens. Could be something like F1.4, F1.8, something like that. 

The thing to note about changing the aperture is that it changes the Depth of Field. More terminology? Sorry. 

Depth of Field is just how much of the image is in focus. Again, get out and practice this, but with a small ‘F’ number/wide aperture you’re going to get a shallower Depth of Field. The subject will be in focus, but the background will be blurred. This blurring is called ‘Bokeh’.

How shallow that depth is, depends on the 'F' number selected and the lens you’re using. Lenses are all different, so practice with what you have.      
Next, Shutter Speed

The next bit is all about shutter speed. And, again, we can practice this as we go. Shutter priority is explained at the bottom of the blog. 

The way a camera works is, we press the wee button on the body and the camera does all its wizardry. Once that’s all good, it opens the shutter to allow the light to hit the sensor, which then records the image. 

Think about shutter speed as blinking your eye. The faster the shutter speed, the faster ‘blink’ the camera will carry out. 

It’s displayed as fractions of a second and, depending on your equipment, you can get up to and beyond 1/4000th of a second, all the way down to something called ‘Bulb’. Bulb is a mode that opens the shutter until you close it again. Why on earth would we need that mode? Well, I’ll tell you. 

What kind of photography do you want to do? Landscape? Sport? Street? Astro? The list is endless and playing with your shutter speed allows you to handle any genre you fancy.  

For example, if we were shooting a dog running, we might want to get a really sharp, crisp image of him as he comes back with his ball. To get that perfectly still image in a dynamic environment, we’re going to need a fast shutter speed. We’re going to find ourselves up in the 1/4000th of a second range, which will freeze the action.

But what if we wanted a bit more drama in the shot? If we step the shutter speed down a bit, we can introduce a bit of blur to the shot and show movement. Why is this? Your sensor records everything that hits it while the shutter is open. So, when the shutter opens for that fraction of a second, the cyclist will have moved a physical distance over the ground, which is recorded as blur in your image. 

How else can we use shutter speed? We can go to the other end of the spectrum and have the shutter open for an extended period of time, say 2-3 seconds. If our sensor records everything while the shutter is open it means we’re going to get a ton of light entering the camera and potentially overexposing the shot. But long exposure can produce some really lovely images.  

Images of water that looks all glassy and smooth is done using this ‘long-exposure’ method and you can play with ‘light trails’ as well. You can also use it in property shoots to improve the light in a dark room. Be careful though as the windows will be ‘blown out’ or over-exposed with this method. 

Experiment with the settings for long-exposure, but if you’re trying it during the day, you’re going to need some Neutral Density (ND) filters. These are basically sunglasses for your camera. The higher the number on the filter the less light they let in and the longer you can expose for. 


ISO is a measure of how sensitive your sensor is to light. The higher the number, the more sensitive it is.  

Modern cameras are getting better all the time and have some huge ISO numbers, so why is this a thing? 

With higher ISO numbers, our sensor is really sensitive, and we can start to introduce something called ‘noise’. This makes your images look grainy and indistinct. It can be an effective artistic tool, but we’ll think about that later. Higher ISO numbers are used in darker conditions to help lift the brightness of an image. 

I like images that look pristine, so I always aim to use as low an ISO as possible in the conditions and just play with the aperture and shutter speed. All cameras are different in their abilities though. I use Sony equipment and they’re pretty good at higher ISOs. 

So, to bring it all together, if we want to shoot a sporting scene, something with a lot of movement, in good conditions and we want a perfectly focused still image, how do we do it? 

We would set a fast shutter speed and keep the ISO low, to keep the noise to a minimum. Then we would play with the aperture, to get the proper exposure for the image, and snap away to our hearts content. 

If we were shooting a property in the winter and the house lights weren’t particularly bright, we would look at a relatively slow shutter speed and with a slightly higher ISO. More light will enter the camera and the sensor is more sensitive. As far as aperture goes, with regards to property, we need a wide enough aperture to let light in, but small enough to make sure the whole room is in focus. 

It’s all about the balance. 

Happy practicing, 



Shutter Priority: Shutter speed is set, and the camera decides aperture and ISO to get a correctly exposed image.

Aperture Priority: Aperture is set, and the camera decides shutter speed and ISO to get a correctly exposed image.

Manual Mode: You control all three sides of the triangle, so you’ll get the same results every time. 

Auto Mode: The camera decides everything to get a correctly exposed image

A full version with photos can be found HERE