What Is ISO In Photography? All You Need To Know. Hi and a very warm welcome to Episode 157 of the Photography Explained podcast. I’m your host Rick, and in each episode, I will try to explain one photographic thing to you in plain English, in less than 27 minutes (ish), without the irrelevant details. I’m a professionally qualified photographer based in England with a lifetime of photographic experience which I share with you on my podcast.
First – here is the answery bit
ISO in photography refers to the sensitivity of the camera sensor to light. ISO is a camera setting that allows you to make a picture brighter or darker. The ISO setting helps you to use different apertures and shutter speed combinations to get the correct exposure in varying lighting conditions. The ISO setting enables you to use faster shutter speeds in low-light conditions. ISO is one of the three elements of the exposure triangle, the others being aperture and shutter speed.
The aperture and shutter speed controls the amount of light that reaches the camera sensor. ISO changes how the sensor processes the light, making an image brighter or darker.
Lower ISO settings give higher-quality images than higher ISO settings. Higher ISO settings can introduce digital noise into photos.
Changing the ISO does not change the sensitivity of the sensor – more on that in a bit.
That was my answer. And this is the talky bit.
Before I go on, if you have a question you would like me to answer head over to photographyexplainedpodcast.com where you can find out what to do.
Yes, a podcast episode all about ISO. I’m sorry, I have to do this. But this is important OK?
You can listen to this episode here
Or read on – entirely up to you
What does ISO stand for?
ISO actually stands for International Organisation for Standardisation. It is not the International Standards Organisation, which would make more sense. And is what I thought it stood for. Oh well, every day is a school day!
“ISO (International Organization for Standardization) is an independent, non-governmental international organization with a membership of 168 national standards bodies.”
Their words, not mine. You can find out more about them at their website iso.org. That is where that statement is from. And what a great web address.
Now I don’t need to say any more about these good folks, not in a “What is ISO in photography” podcast episode.
ISO in photography comes from the camera film days. And I will come onto that in the “What if I use a film camera” bit.
Actually no – I will do that now, don’t worry, there is a reason for this.
So, What if I use a film camera?
Simple. ISO is absolutely fundamental as you buy camera films with different ISOs. This is the old-school general rule of thumb from when I used to shoot film. And these are the films that I used.
- ISO64 – high-quality slide images – a low ISO value
- ISO100 – used for general day-to-day photography
- ISO400 – used for fast-moving subjects/ lower light – 2 stops faster than ISO100
- ISO1600 – used for lower light only – 4 stops faster than ISO100
And that was it for me as a film photographer. I might have used ISO3200 film, but that was in extreme circumstances, and only once or twice. No, I never needed to use higher ISO values, not even for night photography.
But that was ISO back in the film days, nice and easy to understand.
Bear with me on the film example, as the numbers help explain how this has ended up in the digital photography world as it is. And will hopefully simplify this for you.
Why the different camera film speeds?
Simple. I used ISO100 film for general use day-to-day photography. And if I needed to take photos in lower light, I would need a higher-rated ISO film to be able to get the correct exposure when shooting handheld.
Shutter speed
If the shutter speed using ISO100 was say 1/15th second, changing to ISO400 film would mean that I could use a shutter speed 2 stops faster, which would be 1/60th second. Fine for general handheld shooting.
And if I wanted to photograph something fast moving ISO400 gave me a shutter speed which was 2 stops faster. So 1/125th second would become 1/500th second.
And going from ISO 100 to ISO 1600 was a 4-stop jump.
So you could change from 1/15th second to 1/250th second.
Or from ¼ second to 1/60th second.
Or from 1/125th second to 1/2000th second.
You get the idea. What I am talking about here is how I used ISO when I was a photographer taking photos with film.
What about the aperture?
Well, the same applies – a higher ISO film allowed you to use a smaller aperture (at the same light levels), adjusted using stop increments.
But in bright lighting conditions, you did not want ISO 1600, as the camera film would be too sensitive to light, resulting in overexposed photos. So that is where ISO100 comes into play.
That is the origin of ISO in photography. Camera film speeds.
And I will say it again. I used ISO64 slide film, and ISO100 or 400 film for general use. And that covered probably 95% of all my film photography. I dabbled with ISO1600 film, but no more.
So let us not forget this – we can apply the principles of what I did back in the film days to now and digital cameras.
Which is this. ISO now is a camera setting that we can adjust to change the exposure. Change the ISO and it changes the exposure. Change the ISO and the aperture and/ or shutter speed and you can get a correct exposure using different camera settings.
Why do we still have the term ISO?
Well, film cameras evolved into digital cameras, and all these terms from pre-digital days came from those days. You need to remember that not that long ago digital was not even a thing. So we have brought ISO from film days into modern digital cameras, which with hindsight might not have been the most logical thing to do in my opinion. But I get how and why this happened.
So ISO was the sensitivity of the camera film and is now the sensitivity of the camera sensor to light. Sort of.
Does changing the ISO change the sensitivity of the camera sensor?
No it does not. Change the ISO from 100 to 200 and you are making the image twice as bright. This is done electronically. You are not changing the sensitivity of the camera sensor, that is fixed. You are using a different ISO value to make an image brighter. Twice as bright. One stop.
I know it is all rather confusing, isn’t it?
But that is it.
Think of ISO more as an amplification of the light that has reached the sensor.
Now I have in the past said that changing the ISO changes the sensitivity of the camera sensor to light, but that is not technically correct.
So there you have it, once and for all.
To be clear.
The aperture controls the amount of light that gets through the lens opening to the sensor. You can make the aperture larger or smaller, letting more or less light reach the sensor.
The shutter speed controls the amount of light that gets through to the camera sensor by varying the time that the sensor is exposed to light. You can change the time by using a faster or slower shutter speed, letting less or more light reach the sensor.
Aperture and shutter speed control the amount of light that gets through to the camera sensor when you take a photo.
ISO changes how the camera sensor processes the light once it has reached the camera sensor.
So what does this mean?
Well, you could say that nothing changes. But I tell you what a great change would be. Change the term ISO for brightness. That would do nicely for me.
ISO as a term in digital photography is not helpful. I will come back to this in a minute.
What is the ISO Range?
As with aperture and shutter speed, there is an ISO Range. This is it. Dull section alert.
- ISO 100
- ISO 200
- ISO 400
- ISO 800
- ISO 1600
- ISO 3200
- ISO 6400
Each of these adjustments is 1 stop. Going from ISO100 to 200 makes the image twice as bright. I will come onto this in the next episode.
What does the number actually mean?
I have no idea what the ISO number 100 actually means. Shutter speed I am fine with. The aperture is the same, no idea what the numbers actually mean.
But this does not concern me, I am fine with this.
And here is my alternative brightness scale.
- 1
- 2
- 3
- 4
- 5
- 6
- 7
- 8
- 9
- 10
Genius. 1 – 10. It serves the same purpose as the ISO scale.
OK – that is the difficult bit out of the way. Now for some practical stuff.
Which ISO should I use?
In general terms, the lower the ISO you use the better.
What is wrong with using a high ISO all the time?
Well, you get digital noise in photos if you use a high ISO setting. Noise is a bit like grain. It does not look good. And the higher the ISO you use the more noise you get.
I call noise digital bad stuff.
If you have a digital camera you can very quickly do this yourself. Take a photo at the lowest ISO that you can to get a correct exposure, then do the same using the highest ISO that you can to get a correct exposure.
And compare the two.
Look in the shadows, that is where the bad stuff is more prominent.
We don’t want noise in our photos. Having said that
Blurry vs Noisy
It is better to get a noisy photo than a blurry photo. If you have to use a higher ISO to get a sharp image that is better than using a slower shutter speed and getting a blurry picture.
No one outside of us photographers know what noise is, but everyone knows what a blurry photo looks like. So if the only way to get a sharp photo is by pushing the ISO value to a higher number do it – you might be able to deal with the noise in whatever you use to edit your photos. There is some pretty effective noise reduction software out there, but it is of course much better to get things right in camera.
But this is not the recommended approach all the time. Use the lowest ISO that you can that allows you to take sharp photos. Or put your camera on a tripod or other device and the problem goes away. This is what I have always done when there has not been enough light, this is the old-school way!
What is a good ISO?
A low ISO.
What is a bad ISO?
A very high ISO.
Do I change the ISO before the aperture or shutter speed?
No. Get the exposure that you want using the aperture and shutter speed, and if you can’t get a fast enough shutter speed for example, you might change the ISO so you can get a faster shutter speed.
But remember, the higher the ISO value the greater the chance of noise.
When should I change the ISO?
When you have to. When it is too dark.
Let’s not forget if it is really bright, say on a sunny day, you might have to choose a lower ISO to stop getting overexposed photos.
Too light, too dark, or when it is your only way of getting the aperture and/ or shutter speed that you want for a photo.
You could change the ISO to enable you to use a faster shutter speed, either to eliminate camera shake or photograph something moving quickly.
Or you could change the ISO to enable you to use a smaller aperture to get more depth of field. Or to use a larger aperture to get less depth of field!
This is why it is important to understand this stuff, and how the various camera settings can help us get the best photos that we can.
What about the different camera modes?
Mirrorless cameras and DSLR cameras have many different picture-taking modes.
- in some automatic modes, the camera chooses the ISO for you – this is called auto ISO. And for some other modes, you choose the ISO yourself.
- In semi-automatic modes, you choose the ISO.
- And in manual mode, you also choose the ISO.
What is base ISO?
Base ISO is the ISO where there is no amplification. I believe it is ISO100 on my Canon 6D. Logic tells me that this is the ISO that I should be using. Which I am. Which is good. And it is a low ISO setting which makes sense.
Why is it still called ISO?
Good question. I do not know.
Ok – I think that I am done there.
Right – talky bit over – what if I use a phone and not a camera?
I have an iPhone XS (still). I cannot change the ISO using the default camera app. What the phone does is this. Apparently. It tries to choose a low ISO and a fast shutter speed. Makes sense.
Using the Lightroom Mobile camera app in Pro mode I can change the ISO from 25 to 2000.
But I have never done this.
What if I use a film camera?
I think that I have covered this. Just one more thing to say. If you need to change your ISO you have to change the camera film. That is it. No other choice. So you need to know what film speed you need before you start out.
And this is where all those other skills come into play.
What do I do?
I use ISO100. I take as many photos as I can with my full-frame camera on a tripod. I only change the ISO when I have to. I use aperture priority mode (AV Mode) I will use the lowest ISO that I can to get a sharp photo when shooting handheld. In low-light conditions, I simply put my camera on a tripod. I never use high ISO values.
And that is ISO for me. See it does not have to be complicated.
Oh sorry, what about taking photos with my phone?
I don’t even think about it – I just press the “button” – it’s not a button, of course, it is an area of the touchscreen assigned to taking a photo – I just take a photo and move on.
Some thoughts from listeners and subscribers
Subscribers to my weekly email that is – the question – “Does changing the ISO change the camera sensor sensitivity?”
- Nalen – incorrect answer – you thought the same as me. So we have both learned something.
- Terry in NSW – spot on as ever – great knowledge.
- Steve in Kansas – “Much like increasing the volume to your stereo speakers doesn’t change the speakers, but the strength of the signal”. Great analogy Steve – thanks.
And if you would like to receive a weekly email from me, and why not eh, just head over to rickmcevoyphotography.com. And if you would like your thoughts in including in a future episode head over to the podcast website.
Some thoughts from the last episode
Episode 156 was What Are Shutter And Shutter Speed In Photography?
I did not get off to a great start by describing it as episode 155. Another new mistake I have found to make!
Not a lot more to say really. Move on Rick.
Next episode
Episode 158 – well all that is left for me to do is go back to the exposure triangle, where I put together the aperture, shutter speed and ISO. Really looking forward to that episode, which will be Photography Explained Podcast Episode 158 – My Beginner’s Guide To The Exposure Triangle.
Ask me a question
If you have a question you would like me to answer just head over to the podcast website – photographyexplainedpodcast.com/start where you can find out what to do. Or just say hi. It would be lovely to hear from you.
That’s all.
This episode was brought to you by, erm, for a change, a cheese and pickle sandwich and shock horror no crisps washed down with a nice cold Diet Pepsi before I settled down in my homemade, acoustically cushioned, technologically sound recording emporium. Today’s acoustic treatment is four pillows and two fleeces – I have gone for it this episode!
I’ve been Rick McEvoy, thanks again very much for listening to my small but perfectly formed podcast (it says here), and for giving me 27 ish minutes of your valuable time. I think this episode will be 27 minutes long after I have edited out the mistakes and other bad stuff.
Take care, stay safe
Cheers from me Rick
OK – that was the podcast episode.
Want to know more?
Head over to the Start page on the Photography Explained Podcast website to find out more.
And here is the list of episodes published to date – you can listen to any episode straight from this page which is nice.
Let me know if there is a photography thing that you want me to explain and I will add it to my list. Just head over to the This is my list of things to explain page of this website to see what is on there already.
Let me send you stuff
I send out a weekly email to my subscribers. It is my take on one photography thing, plus what I have been writing and talking about. Just fill in the box and you can get my weekly photographic musings straight to your inbox. Which is nice.
And finally a little bit about me
Finally, yes this paragraph is all about me – check out my Rick McEvoy Photography website to find out more about me and my architectural, construction, real estate and travel photography work. I also write about general photography stuff, all in plain English without the irrelevant detail.
Thank you
Thanks for listening to my podcast (if you did) and reading this blog post (which I assume you have done as you are reading this).
Cheers from me Rick
