Understanding the 3 points of the exposure triangle

So, what is the exposure triangle?

Well the exposure triangle is the relationship between aperture, shutter speed and ISO.
Each one affects the other.

OHM’s Law

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.

The Three Points of the Exposure Triangle

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.

Let’s say you took 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. The subject will be in the focus but the background will be blurry.

But if you took a picture with a small hole e.g. a setting of F22. then everything will be in focus. That’s not strictly true as the amount in focus starts at the point at which you are focusing the camera out towards, potentially, infinity. 

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 setting of 1/100 is one hundredth of a second or .001. A setting of 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.

3. ISO

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 ISO 25600 plus is the most sensitive.

Practical Example

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 we’ve got this new beaut product that we want to take to the market place and we want to create some really cool images to use for marketing.
Let’s say it’s this toy soldier
We’re taking the picture inside which is fairly bright, even though we’re using just natural light. To make sure we get a properly exposed image we are going to take a couple at different settings.

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 look closely and you’ll see that it looks 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. Here 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.
That’s because 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.

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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, with newer cameras the higher the maximum ISO setting on the camera the less likely noise will occur at lower settings. E.G. The OMD1 MKII Mirrorless Camera that I have, has a maximum setting of 25600. Realistically I don’t really see any noise in an image until around 1000. Compare that with my Galaxy S8 Smartphone Camera that has a maximum ISO of 800. With this one I notice noise at around 400 ISO

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

Thanks for reading this article

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