Understanding the 3 points of the exposure triangle

Understanding the 3 points of the exposure triangle

Understanding the 3 points of the exposure triangle

So, what is the exposure triangle?

Well it’s the relationship between aperture, shutter speed and ISO.

Each one affects the other.

Remember Ohm’s law? Well if you don’t (I’m not even sure they teach it at school these days).

It’s basically an electrical equation V Volts (power) = R Ohms (resistance) x I Amps (current) and if you change one you change the other.

If you know the power and the resistance then by changing the equation to Volts ÷ Ohms = Amps, you can work out the current (amps).

Understanding the 3 points of the exposure triangle




It’s the same for the exposure triangle.

Let’s see if we can remember this easily.

1 Aperture

Aperture is a hole that lets light in. The bigger the hole the more light you let in.

What does that mean?

It means the smaller the hole the more in focus – the bigger the hole the less in focus.

If you take a picture with a setting of F2.4 (because the size of the hole is inversely proportional to its setting) that’s a large hole and the subject will be in the focus but the background will be blurry

If you take a picture with a small hole e.g. a setting of F22 then the more you will have in focus from the point at which you are focusing the camera back towards, potentially, infinity

For more on the topic of aperture go to 10 Vital Facts about Camera Aperture

2 Shutter speed

This is an easier one to grasp.

As with the aperture, the longer the shutter is open the more light you allow in.

Shutter speeds are measured in fractions of second to seconds.

So, a shutter speed of 1/100 is one hundredth of a second or .001. Obviously 5 is 5 seconds.

However, the effect is totally different from the aperture. A fast shutter speed will generally freeze motion e.g. sports. Whilst a slow shutter speed will blur motion e.g. a fluid looking waterfall.


ISO stands for International Organization for Standardization and in the film days was an indicator of how sensitive to light a film was.

An ISO 400 film was 4 times as sensitive to light than a ISO 100 film.

On digital cameras that sensitivity is for the camera sensor.

When the ISO is increased or decreased you are in effect making the camera sensor more or less sensitive to light.

ISO 100 being the least sensitive whilst is the most sensitive.

So, there you have the three points of the exposure triangle.

I’ve already mentioned how each one affects the other but let’s see how that affects, for example, Product photography and look at a couple of specific examples.

OK, so you’ve got this new beaut product that you want to take to the market place and you want to create some really cool images to use for marketing.

And let’s say it’s this toy soldier.

You’re taking the picture inside which is fairly bright, even though you’re using just natural light.

 Understanding the 3 points of the exposure triangle

The first image has an aperture of f5 and a ISO of 800 whilst the camera has calculated the shutter speed.

You can see everything is in focus and the light looks fairly normal.

But doesn’t it look a bit soft e.g. slightly blurred?

That’s because the shutter speed is too low at 1/20 which means I couldn’t hold it still enough.

 Understanding the 3 points of the exposure triangle

The second image had an aperture of f1.2 and a ISO of 2000 there you can see that the soldier is in focus whilst the background is blurred (bokeh).

That’s a fairly common way for ensuring that the spotlight is on the product and not distracted by the back ground.

Because of the high ISO the shutter speed is 1/200 which means the image is much sharper as the shutter speed is now 10 times as fast and is a bit more forgiving.

As an aside if you think you can hold a camera still regardless, think again. Our hands move without us knowing.

However, the disadvantage of having a high ISO is that the image could have noise which may or may not be an issue.

As a rule of thumb, the higher the maximum ISO setting on the camera the less likely noise will occur at lower settings.

In other words, if you have camera that goes to a maximum setting of 100,000 the noise factor at 5000 will be almost non-existent.

If on the other hand, you have a camera that has a maximum setting of 10,000 then the you will be able to see noise at 2000.

Of course, there are ways of reducing or getting rid of noise in post-production with software like Adobe Lightroom. So, it’s not a big issue.

Below are two examples of noise from two different cameras.

 Understanding the 3 points of the exposure triangle


Understanding the 3 points of the exposure triangle

There you have it, that’s the exposure triangle.


Did you understand all that? I’m happy to clarify anything you’re not sure of.
Just post in the comments section below. Don’t be shy.
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