Camera ISO and understanding exposure is complex, so let’s start right at the beginning.
You may have read on other photography courses about the exposure triangle. FORGET ALL OF IT.
Whilst this can be a useful visual aid, it’s important to know that it is technically incorrect.
Exposure is constituted by the amount of light that lands on the camera sensor or piece of film, the shutter speed and the aperture are the only two factors that control this.
Increasing the ISO will make the image brighter, but it’s important that you understand why and how it’s different to controlling the shutter speed and aperture.
It’s not because the camera is absorbing more light, it’s because the sensor is boosting the signal it is receiving artificially.
Why is this important?
Because it produces what we call ‘noise’.
Noise looks like this:
When we zoom in on an image where a high ISO has been used, we can see that the detail begins to break up.
This is noise.
So, whilst increasing the ISO will make the image brighter, you have a trade off with image quality.
A camera TECHNICALLY only has one ISO setting.
BUT.
Much like when you turn the volume up on an analogue radio, the signal from the radio station hasn’t increased, you have merely upped the output of the radio, which then means you’ve still got a rubbish sound, you’ve just made it louder.
For argument’s sake though, when we talk about increasing the ISO, I’ll be referring to increasing the number.
How do you pronounce ISO?
ISO comes from the Greek ‘Isos’ and is pronounced “Iso”. It’s not an acronym, so it’s not I.S.O. but “eye-so”.
An introduction to ISO settings in photography
Exposure is difficult to understand, so don’t put too much pressure on yourself.
It takes a long time to master a new skill, so take your time.
I say that because in my years of teaching I’ve seen students lean too heavily on ISO because it seems like an easy way out to get a brighter image. This is typically because they’ve struggled to grasp how the mechanical elements of a camera work first, so they use ISO as a quick fix.
This article is designed to answer common questions such as:
- What is ISO on a camera?
- What is ISO in photography?
- What does ISO stand for in photography?
- How does ISO affect a photo?
- Should I always choose the lowest ISO?
- How does ISO make an image brighter?
What is ISO?
ISO is a measure of the sensitivity of the image sensor, or piece of film – that’s it.
The higher the ISO number, the brighter the image.
What is ISO on a camera
ISO is an important factor when determining the correct exposure for your photograph.
As you increase the ISO, the image will become brighter, but the ‘grain’ (also called noise) on the image also increases.
The higher the ISO, the brighter the image, but the lower the image quality.
This is why ISO should typically be the last setting you look to change when considering the exposure of the image.
Take this scene for example.
My lens is set to let in the most light that it possibly can (in this case it’s f/4)
I need a shutter speed above 1/60 otherwise the movement of my hands will shake the camera, and the image will be blurry.
So I have no choice but to increase the ISO.
ISO 3200 was too dark, ISO 12,800 was too bright. The correct exposure in this example, was ISO 6400.
ISO in film photography
In film photography, ISO (or sometimes ASA) indicates how sensitive the film is to light.
The ISO of the film is fixed, so you need to know what you will be photographing beforehand so you can take the appropriate film, once it’s in the camera, you can’t take it back out until the film is finished.
The lower the ISO number, the lower the sensitivity of the film.
ISO 100 for example, would be used for daylight. I used to use ISO 800 film for shooting boxing matches.
The distortion of the image from shooting at a high ISO film is referred to as Grain, in digital photography, it is called noise.
ISO in digital photography
In digital photography, ISO measures the sensitivity of the image sensor.
It’s exactly the same as film photography, apart from the fact that the ISO can be changed from one picture to the next.
The lower the number, the less sensitive your camera is to light.
Again, ISO 100 would be used for daylight, higher ISO’s would be used in darker situations, such as photographing indoors.
How Does ISO affect exposure?
The lowest setting on the vast majority of digital cameras is ISO 100.
In film photography the ISO would double from 100 to 200, 200 to 400 etc.
Doubling the ISO doubles the sensitivity of the sensor, so ISO 200 gathers light twice as fast as ISO 100.
Doubling the ISO means that the image will be twice as bright.
Halving the ISO halves the sensitivity of the sensor, so ISO 100 gathers half as fast as ISO 200.
Halving the ISO means the image will be half as bright.
However, modern digital cameras often allow increases in ISO in smaller increments.
Increases such as 100, 125, 160, 200, 250, 320 etc. to allow for finer adjustments of the exposure.
That being said, I recommend you go into your cameras settings and change the exposure increments to full stops as it makes it easier to get your head round exposure if the numbers are simply doubling and halving each time.
The Trade Off – ISO settings and grain/noise
When you increase the ISO, you are compromising image quality.
How and why?
Have you ever heard static sounds from a radio? That buzzing, crackling sound? Imagine if you turned the volume up on that sound, it wouldn’t become clearer, it would be louder and more pronounced…and more annoying.
Digital noise (also called grain) is effectively the same as this, but it happens visually.
As you increase the ISO, you are ‘turning up’ the signal artificially.
To illustrate this, here are some example images taken using different ISO settings.
Image 1 – ISO 100 – A low ISO
This picture was taken in a conservatory, so lots of light available, and it was a summers day. When there is lots of light available, we use a low ISO.
When zooming in, we can see that using a low ISO of ISO 100 has produced very clear details. The wrinkles of the hand and the weave of the cloth are both visible.
This next picture was taken in a dark church…a very dark church.
Image 2 – ISO 8000 – a very high ISO
On the close up we can see how the detail is lost. By increasing the ISO to this extreme we are telling the camera to boost the the exposure artificially, so the result is this crackly effect.
See the difference between the two?
One has clear, clean details. The other contains a great deal of noise which affects the clarity of the image and detail is lost.
Image 1 – ISO 100
Image 2 – ISO 8000
To appreciate how dark the church was, we can list the ISO scale. Where each time the ISO is doubled, the brightness is doubled:
100
200
400
800
1600
3200
6400
(in between 6400 and 12800 – 8000)
12800
So that’s approximately six and a half times darker.
It affects image quality, so why would you use it?
High ISO’s give you options when light is limited.
If you are photographing a wedding in a dark church, the minister says you can’t use flash and there are no windows.
Your options are limited by the shooting situation, so you have to work with what’s available.
If you have the ISO set to 100, and your camera light meter is telling you correct exposure would require an aperture of f/2.8 (lets say in this scenario, that’s the maximum aperture your lens can achieve) and a shutter speed of 1/10th of a second.
The aperture can’t go any wider to let any more light in, and that shutter speed will cause the images to have motion blur as it’s difficult to hold the camera still when the shutter is open for that long.
Your only option left is to increase the ISO.
Do I have any other options?
In the above scenario, no.
However if you were shooting a subject that doesn’t move, you could use a tripod.
If you were shooting in an environment that gave you more control, you could use flash or another light source.
What to consider when choosing ISO:
- When selecting your ISO, there are a few things to consider:
- Light – How much light is available?
- Grain – Does it matter if the final image is grainy?
- Tripod – Can I use a tripod?
- Movement – Is the subject moving, or is the scene still?
Examples of shooting situations that often require high ISO
- Live music events – whilst bright lights illuminate the musicians, it’s still nowhere near as bright as daylight. Depending on the genre of music, the musicians may move a lot, so a fast shutter speed is going to be needed. Expect not to be able to use flash either.
- Art Galleries – flash is typically not allowed as the constant exposure to intense light fades the painting (light is radiation after all), and low light in the gallery as a whole should be expected for the same reasons, plus they are often illuminated in a way that lends atmosphere to the exhibition.
- Churches – Intensely atmospheric, and often with huge windows, there is still a distinct lack of daylight streaming through. Thick, dark stone walls absorb a lot of the light, plus churches are huge so it takes a considerable amount of light to penetrate into the deep recesses. Throw into the mix a bride walking down the aisle and you’ll need a high ISO to give you a fast shutter speed to freeze her movement as she walks.
Understanding ISO and its relationship with Aperture and Shutter speed is vital for taking control of your camera and taking better photographs. As important as it is to have a firm understanding on paper, you MUST experiment with your camera, as understanding how light changes, and how it affects your images in the real world, is the only way you will truly master exposure.
Conclusion
The higher the ISO, the brighter the image.
Always look to achieve correct exposure with the shutter speed and aperture first. Only change the ISO when all other options have been exhausted as high ISOs create lots of noise and reduce image quality.