What is ISO in photography?
If you are a beginner, wishing to learn photography and looking to improve your pictures, a better understanding of the technique and related terms is in my opinion necessary. This article is a continuation of the most important article for understanding the basics of photography: the exposure in photography. Indeed, ISO sensitivity is one of the three parameters of the exposure triangle (along with shutter speed and aperture).
In my opinion, this is the easiest parameter of the three to understand. I remember when I started out in photography, looking up “photo iso” or “camera iso” on Google to try to understand what these three letters (I.S.O) meant and how they could influence my pictures.
In this article, again a bit technical, I will first explain what ISO in photography is and how it works. I will then explain how to adjust and change the setting. Then the influence of ISO sensitivity on your photos and how to determine the ideal setting will be explained. Finally, I will end the article by giving you a practical use of ISOs in photography (when to use a certain setting depending on the scene) and advice/precisions regarding the camera equipment on this point. Don’t worry, you don’t need to be a professional photographer to understand the idea. Here we go.
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Definitions and basics of ISO sensitivity
I explained to you that this was the easiest parameter of the exposure triangle to understand. So what are ISOs in photography? It is simply the “sensitivity of your camera’s sensor to light”. Let’s say that ISO is “a tool” telling you camera how bright your picture should be, for a given exposure. To put it in perspective, at the time it was the sensitivity of the film. So what does the term ISO mean? International Organization for Standardization, it is simply a measure to evaluate the light that reaches the sensor.
Unlike the other two parameters of the exposure triangle, ISOs are measured on a simple and easy to understand scale. Here, below, are the standard ISO values found on cameras, as a general rule.
ISO 50 – 100 – 200 – 400 – 800 – 1 600 – 3 200 – 6 400 – 12 800 – 25 600 – 51 200 – 102 400
Remember, as explained in the article on exposure, as soon as you double a parameter, the amount of light is also doubled. In concrete terms, if you go from ISO 100 to ISO 200, you have twice as much light reaching your camera’s sensor. Keep in mind that the higher the ISO number, the more sensitive your sensor is to light. You’re going to tell me, what does that actually mean? I’ll tell you more about it below, but the general idea is this:
- If your scene is low-light, you’re going to have to make your sensor more sensitive to pick up light, so increase the ISO,
- Conversely, if your scene is very bright, you do not need to make your sensor sensitive to light since the ambient light is sufficient. You will then set the ISO to the lowest setting.
The principle of using ISOs is therefore very simple in itself, but there is a problem. The appearance of “digital noise” when high ISOs are used. I won’t go into the details of the appearance of noise here, but keep in mind that it is a kind of grain that appears on your pictures, especially in dark or plain areas, which brings a very unattractive side to the photo. I will explain at the bottom of the article, the relationship between ISO sensitivity and camera equipment.
The difficulty in using ISO sensitivity will be the following: choosing the lowest ISOs to avoid grain in our photos while adjusting to the scene in front of us. I can already see you thinking “why not just use a low ISO all the time, so I never get noise? ». The concern is that depending on the shooting conditions, using a low ISO (eg: ISO 100), will be impossible, because the shutter speed to take the picture will be not enough to get a sharp picture. I go into detail in the paragraphs below, but remember this:
ISOs should be used as a last resort once all the other parameters are “at their maximum” to bring in light (maximum aperture and slower shutter speed).
How to adjust and change ISOs?
Once we know the basics and what ISOs are used for in photography, let’s now look at how to change or set the ISO sensitivity. I’m not going to make things any more complicated than they actually are. It’s very simple. You have two cases:
- Either you use an “auto ISO” mode, which is found in several camera modes (Aperture Priority/Speed Priority or auto mode). In this case, you decide to set only one setting and the camera can set the ISOs automatically,
- Either, and this is the case that interests us the most, you will manually set your ISOs (in manual or semi-automatic mode – Av/TV type at Canon). Usually, on all DSLR/mirrorless cameras, you have an ISO button on the top of your camera body that allows you to increase or decrease the ISO using the button..
The setup itself is no more complicated than that.
The influence of ISO sensitivity: the noise
Once the basics have been learned and the ISO settings understood, let’s take a look at the influence of ISO sensitivity. As I mentioned above, the goal will be to limit the appearance of noise on your photo as much as possible (unless it is voluntarily desired), in other words, avoid raising the ISO to the maximum. The noise will not necessarily be visible on a computer in full screen, check out the photos below taken at ISO 400, ISO 5000, ISO 20 000. Do you see a real difference?
Note that I deliberately used extremes for this example, because the Canon 6D handles high ISO so well that if I had chosen ISO 100, ISO 400 and ISO 3200, you really wouldn’t have seen any difference.
The noise appears as soon as you zoom in to look at a detail. Now judge the same two pictures when zoomed at 100%, at ISO 400 on the left and ISO 20,000 on the right. This is what it would look like if you printed the photo in full size.
As you can see, the noise appears more clearly in the darker areas of the photo. The more I increase the ISOs, the more you see this very unattractive noise appear.
I admit that the adjustment between the 2 photos is not perfect but you can see the noise that appears, right?
How to determine the maximum ISO sensitivity to use?
There are no miracle recipes, but remember the following principles:
- Stay as long as you can at the lowest ISO (ISO 100 or 50 on some DSLRs) to avoid noise as much as possible,
- When the light conditions decline, you will have no choice but to increase the ISOs to ensure that your camera’s sensor can pick up more light. If you don’t do this, overall, the majority of your pictures will be blurred (except on a tripod),
- The 3 parameters (ISO, shutter speed, aperture) of the exposure triangle are related. You therefore have 2 other possibilities to let more light into your camera, before you have to increase the ISOs,
- Doubling or halving ISOs allows you to multiply or halve the amount of light reaching the sensor. In practical terms, this allows you to adjust one of the other two parameters (aperture or shutter speed). In fact, if you double the ISOs and leave the other two parameters the same, the photo will be too bright (overexposed).
So, to avoid having to increase the ISO (looking for more light), you have two possibilities. Understand that in the 2 cases mentioned below, doubling the ISOs or changing the parameter is identical from the point of view of the exposure of the picture but you won’t have the same result. You can do this by:
- Opening your diaphragm one stop (e.g. change from f/14 to f/11),
- Decreasing the exposure time/shutter speed by two (e.g. 1/100 to 1/50).
In the two cases mentioned below, the amount of light reaching the sensor is doubled. To compensate for this excess light, you (or the camera) will have to modify the other parameter.
Ex no.1 : f/11 1/30 ISO 100 -> f/8 1/60 ISO 100
(the shutter speed has been doubled)
Ex no.2 : f/5.6 1/100 ISO 200 -> f/8 1/50 ISO 200
(the aperture was reduced by one stop)
1) Open your diaphragm
This manipulation will reduce your depth of field. Remember (we talk about this in the article about the aperture), the bigger your aperture (small number), the more your depth of field will be reduced (the whole scene will be less sharp everywhere). If you decide to use this technique to limit the ISO increase, this is the main problem you will encounter (the reduction of your depth of field). Depending on the picture you want to shoot, this can become very limiting. I will explain a concrete case to you below.
2) Shooting the picture more slowly
The same principle applies to the second possibility. If you decide to take the photo more slowly to bring in more light, you will soon be faced with the need to use a tripod so that the photo is not blurred. It will not be possible to take sharp pictures below a certain shutter speed without a tripod. To avoid increasing the exposure time, you can double the ISO.
You will notice in both cases that the general idea is to use the higher ISOs only to avoid getting a too limited shutter speed when shooting and to avoid blurred pictures, or to avoid reducing the depth of field. A compromise will have to be found between lowering your aperture a stop or doubling the exposure time for example, and increasing the ISO.
To maintain a very good shutter speed limit mark in photography, you can base it on the focal length you are using. It’s not a universal rule (it also depends on the sensor size), but it’s a reference point that every photographer knows:
Try to keep your shutter speed at least equal to the focal length you’re using.
Example
1/20 for a 20mm focal length
1/100 for a 100mm
1/300 for a 300mm
and so on
I hope I was clear on this part, because it is ultimately the most important part of the article. If you understood that, you understood everything. I still want to offer you concrete cases of ISO use and choice, from the most common to the most complex. This passage is not an obligation to read, but I think it will help you understand things better.
Some concrete cases
Landscape photography - Full sunny day
This is the simplest case for ISOs and the easiest to remember. As mentioned above, you will always try to limit noise. You don’t have to worry about brightness thanks to the sun. You begin by setting your aperture between f/11 and f/14 for your landscape. Then, you just have to set your ISOs at the lowest setting of your camera, which is very often ISO 100 or ISO 50 (as on my 6D). You won’t have to worry about blurred pictures, the shutter speed being (in this situation) always more than enough for the picture to be sharp.
To go further and understand the ISO sensitivity, you can have fun doubling the ISOs at that time. If you’re in Av mode (aperture priority, an easy mode to start with), your camera will halve the exposure time to compensate for the excess light you’ve created by doubling the ISOs. E.g.: you had f/11 ISO 100 1/500, you get f/11 ISO 200 1/1000. Your photo is exposed in the same way and the result is identical (knowing that at ISO 200, there is no noise).
If you now double the ISO (to 400) again, the shutter speed will double to 1/2000. If you double again (ISO 800), you get 1/4000. And there, for many, you will reach the limit of digital cameras, because this is very often the maximum shutter speed limit of your camera. This is a good way to understand the relationship between ISOs and aperture. You can also see that in the middle of the day, for sunny landscape photography, you will never have noise in your pictures (even at ISO 800). So you have nothing to worry about. Just remember to limit yourself to the lowest ISO.
Photo in the middle of the day - large aperture needed
Now let’s take a less common case, which concerns shooting in the middle of the day with a wide aperture, the general idea being to blur the background to highlight a subject (the blur and its quality is called the bokeh). This could be for outdoor portrait shots, or for highlighting a detail of a landscape or an object in the sun.
This is ultimately a simple case in terms of ISO sensitivity. You have light, so you stay at the lowest ISO of your camera. I wanted to bring it up to show you the relationship between ISOs and the two other parameters.
If you want to blur the background, you will for example use a large aperture (f/2.8 for example). You set the ISOs to the lowest, and let the camera display the appropriate shutter speed. Example: f/4 ISO 100 1/2000. If you double the ISOs (for the exercise), the camera will double the shutter speed to 1/4000. You have probably already reached the shutter speed limits of your camera body. If you want to blur the background even more and you decide to switch to f/2.8, but the camera can no longer compensate the shutter speed as it is at its maximum. You are therefore stuck with a picture that will be overexposed. There are techniques for this (using an ND filter), but I won’t talk about them here.
It also shows you the importance of your camera body and the management of its ISO sensitivity. If the camera had the ability to go down to ISO 50, then you could have switched to f/2.8, as the camera will have automatically adjusted the shutter speed to 1/4000.
Sunrise or sunset picture - landscape photography
Let’s take a common example from landscape photographers. They often seek the best light, which is either at sunset or sunrise, the famous Golden Hours. You will generally want a large depth of field (f/11 to f/14). You arrive at a location at the end of the evening, set the aperture to f/16, the camera announces a shutter speed of 1/10s, which handheld is impossible or almost, and you don’t have a tripod (I will explain this later).
To take the picture handheld, you have 2 solutions (knowing that you can compensate by taking twice as fast whatever option you choose):
- Open your diaphragm (larger aperture = smaller number, e.g. f/16 to f/11),
- Double your ISOs so you can double your shutter speed.
This is the case I told you about above. It explains very well the impact and the relationship between ISO / Aperture and depth of field.
You decide to open your diaphragm several stops (e.g. up to f/5.6). In this case, you will be able to gain speed, but your scene won’t be sharp everywhere. But that’s what you wanted in the first place. It will therefore be time to ask yourself if increasing the ISO is not the best choice at this time, rather than opening your aperture.
The trick will be to find a balance. You may decide to open only one stop (f/16 to f/11) which allows you to double the shutter speed, but is that enough? Not sure. In this case, you can always double ISOs at this moment too.
So you’ll have to play with that, because opening your aperture or doubling the ISOs a stop will lead to the same result, that is., being able to double your shutter speed and get a sharp picture. Only, the increase in ISO will at some point bring noise. It depends essentially on the capacity of your camera body to increase the ISO (we talk about it at the end of the article). And opening your diaphragm will lead to a shallower depth of field.
You have your dilemma: reduced depth of field or noise appearance?
Of course, the problem no longer exists once you have a tripod, because you will be able to take a picture at very low speed with a remote control or your self-timer. This also shows you the importance of the management of the rise in ISO by your camera, because otherwise your photo will be blurred or you will have to use a tripod in these conditions.
Daytime picture cloudy/overcast
Here is a case that you will encounter very often, in everyday life or when traveling. In this case, everything will depend on what you want to take a picture of. Do you want to shoot landscape photography? A portrait? Wildlife or flora? A highlighting of a specific subject?
You get the idea, depending on what you want, you will most probably first choose an aperture adapted to the scene and your photographic will.
If you want to highlight a subject and choose a large aperture, you will not have any problem with ISOs in general. At f/2.8, the shutter speed is usually still high enough to take a sharp picture in such a situation. Of course, it all depends on the focal length you use.
If the weather is cloudy, and you want to have a large depth of field (sharp overall, for example landscape photography), you will probably have to increase the ISO. If you use f/11 on your camera body, and the brightness is low, the shutter speed chosen by the camera body may not be enough. As a reminder, recall what was said above. Shutter speed = focal length of your lens.
The longer your focal length, the more you will have to increase your ISO, because the minimum shutter speed necessary to avoid blur will be higher. To put it another way, if you’re doing landscape photography with a 14mm focal length, you can theoretically go as low as 1/10s before the picture is blurred. Conversely, if you have a focal length of 300mm and you are taking pictures of birds, a minimum speed of 1/300 may be required to avoid blur.
On cloudy days, to obtain a speed of 1/300, an increase in ISO will be almost mandatory. Which brings us to the last case, below.
Wildlife photography - the importance of ISO sensitivity and focal length in photography
Last concrete example. I am talking about wildlife photography and in particular two specific personal examples: the photo on safari (Tanzania) and wildlife photography in undergrowth in the jungle in Sumatra (Orangutans). These two examples demonstrate the importance of using ISOs in photography and the relationship with the focal length.
Remember the following: the longer your focal length, the higher the ISO will be required. Why is this? Because, you will have to obtain a high enough shutter speed to avoid a blurred photo and depending on the shooting conditions (full day sun, clouds, etc.), it will simply be impossible.
Example 1: photo on safari in Tanzania
Even if the light conditions are correct in the middle of the day (mostly sunny, sometimes cloudy), I was taking pictures with my Canon 70-300mm L IS. In theory, I had a minimum speed of 1/300 as a reference. This is the minimum, which can be ok for landscape photography in savannah for example or if the animals are steady.
But as soon as you shoot moving or running animals, 1/300s will be too slow and the pictures will turn out blurry. To explain, I usually wanted to isolate the subjects, so I chose the largest aperture I had at 300mm, which was f/5.6. In the middle of the day, with this aperture, with ISOs at the lowest, I sometimes found myself with shutter speeds of 1/200 or 1/300. I was very often too limited if I stayed with my lowest ISOs. If on top of that the sky was a little overcast, the shutter speed was even lower.
What to do in this case, you have no choice but to increase your ISO to be able to double your shutter speed. As a result, the majority of my safari photos were taken between ISO 400 and ISO 800, which still doesn’t generate any noise. The more the light dropped at the end of the evening, the more I had to increase the ISO. At night or at sunrise, I sometimes took pictures at ISO 1600, 3200, even 6400 to get the right speed.
All this was mainly due to the shooting conditions, but also and especially to the focal length I was using (300mm) and its maximum aperture (f/5.6). Once again, you can see the importance of the camera equipment and its relation with the ISO sensitivity. Obviously I wouldn’t have needed to increase my ISO this high if:
- My lens had a larger maximum aperture (f/4 or f/2.8). Remember at f/4, you get twice as much light in as at f/5.6,
- If I used a shorter focal length, which would have required a slower shutter speed when shooting. For example, for landscape photography with my 24mm, I could maintain low shutter speeds and therefore not necessarily go up in ISO.
Which brings me to my example n°2.
Example 2: picture of monkeys in undergrowth
I’ll end on that. We have just seen the importance of the focal length and the maximum aperture in relation to ISOs. A few years ago, I was in the jungle in Indonesia, taking pictures of Orangutans. For the story, I had the same lens (300mm with a maximum aperture of f/5.6) but I didn’t have the same body (500D to start with).
The situation was the following: very low light, need to use a long focal length (the monkeys being far away), and limited by my maximum aperture at f/5.6.
Conclusion? I fully open my aperture (f/5.6) at 300mm. I have a very low shutter speed. I increase my ISO at maximum (ISO 1600), which still brings me a too limited shutter speed, very often below 1/300. So what’s the problem? I was stuck and had reached the limits of my camera equipment, both my lens (limited maximum aperture) and my camera body (raised ISO too low).
Now imagine the following to see if you begin to understand. If I had had a maximum aperture at f/4 instead of f/5.6, what would it have changed? Remember, you double the amount of light in between. The two parameters being linked, I would have been able to take the picture twice as fast at f/4 as at f/5.6. Now imagine that I could have gone up to ISO 3200 (instead of ISO 1600), it was still the same and I could have taken the picture even faster.
See how important camera equipment is in photography too?
The practical use of ISOs in photography: a summary
A quick chapter to summarize. Unfortunately there is no silver bullet and it is impossible to say that you should use such ISO in such a situation. It depends on 4 main elements:
- The shooting conditions (sun, night photo, cloud, etc.),
- The maximum aperture of your lens,
- The increase in ISO of your body and especially the noise management of the latter. An ISO 1600 on my 500D was really more than limit noisewise and the quality was bad. Increasing to IS0 1600 on my 6D is done without thinking as the body manages the noise very well. The difference between the two, you ask? One APS-C body, the other one a Full-Frame, and 1500€ difference…
- The focal length you will be using (because the longer your focal length, the more shutter speed you will need, and therefore potentially higher ISO).
Example of a long focal length requiring very often an increase in ISO to avoid motion blur/camera shake (here a 150-600mm) – More details on Amazon
When to use low ISO?
We talk about low ISO sensitivity between around ISO 50 and ISO 400. You can use it on a sunny or even slightly cloudy day. In good conditions with light, you should use the lowest possible ISO.
In most cases, with a short focal length (less than 100mm for example), a low ISO will be enough to get a nice sharp picture, for example in landscape photography. As soon as you use a long focal length for a specific need (birds, airplane in the sky, etc.), you will have to increase the ISO.
When to use high sensitivity?
Let’s imagine a high ISO sensitivity from ISO 400 or ISO 800. You get it, you will use high ISOs as soon as (here are the most common cases):
- You have already opened your aperture to the maximum,
- You have already reduced the shutter speed to the maximum and you don’t have a tripod to take the picture more slowly,
- You are in a low-light situation that requires you to increase your ISO to avoid blurry photos (night, concert, etc.) and you still don’t have a tripod!
- You want to do special effects on your photos (a bit old school effect with noise… but this can now be done in post-processing very well),
- You are using a long focal length and the conditions are not excellent (e.g.: my orangutans),
- You are limited because of one of the other two parameters of the exposure triangle: small aperture voluntarily desired or high shutter speed required, for example, all in low to very low light conditions.
Limitation in relation to the aperture: I already told you about this above. You absolutely want to keep a small aperture (f/14) for your landscape photography in low light conditions and you don’t have a tripod. You have no other choice but to increase the ISO to get enough shutter speed to avoid motion blur.
Shutter speed limitation: For example, you want to take pictures of planes in the sky, flying birds, animals moving in low light conditions. It is the same concern, if you have to maintain a high shutter speed (Example: 1/2000), you will have no other choice than to increase the ISO.
Example to isolate a flying bird with a 600mm:
- f/2.8 ISO 100 1/500 (not enough speed),
- f/2.8 ISO 200 1/1000 (limit shutter speed if moving fast),
- f/2.8 ISO 400 1/2000
- f/2.8 ISO 800 1/4000
As you can see, if you want to take a picture quickly while keeping a large aperture, the increase in ISO is mandatory to compensate for the lack of light that will reach the camera’s sensor (linked to the high shutter speed).
Camera equipment, shooting and ISO sensitivity
Well, I know this article is very long and I already congratulate those who have managed to read everything so far! I end with a very important point about camera equipment and the connection with ISO sensitivity in photography. You will understand why camera equipment is of great importance with ISOs.
Some key points to remember:
About your camera body
- The increase in ISO of your camera is very important because it allows you to shoot in low light conditions and not to be blocked (as it was the case with my 500D, remember my Orangutans stories). Usually, the higher the ISO of your camera, the better the noise management will be. A typical example is the Full-Frame (24×36), which offers ISO increases up to more than 100 000 ISO,
- Minimum ISOs on your body: This can play its role as well as being able to go down to ISO 50 instead of ISO 100. This is especially interesting for those who want to use large apertures (e.g. f/1.4) in full sunlight. The possibility of ISO 50 makes it possible to shoot even faster and to be less limited by the maximum shutter speed of the camera (often 1/4000),
- The cost of your body: remember that in most cases, a more expensive body will always better manage the increase in ISO and therefore, ultimately, the noise. Full-Frame cameras (compared to aps-c cameras or MFT) manage the increase in ISO much better. Note also that as a general rule, the more expensive the camera is, the more it offers the possibility of high ISO (even if in theory, you will never shoot at ISO 100 000).
Which camera for your use? This is another debate, which I have already partly covered in the article explaining which camera to choose for a trip.
The 6D Mark II, a modern Full Frame cameras that perfectly manages high ISOs – More details on Amazon
About your lenses
- The maximum aperture of your lens: I remind you, the larger the maximum aperture of your lens (a small f/ number), the more you will not necessarily need to increase ISO. Doubling the ISO or opening the aperture by one stop is the same regarding exposure. If you have a very “bright” lens, you won’t need to increase ISO since you will already have more light coming in through your sensor. This is why the price of a lens between f/4 and f/2.8 is doubled,
- The cost of your lens: the previous point necessarily leads to this one. A bright lens is usually expensive, especially for long focal lengths. However, there are very good value for money for very bright lenses such as the Canon 50mm f/1.4 or the Canon 85mm f/1.8. Keep in mind that bright telephoto lenses are expensive (f/2.8),
- The focal length of your lens: I mentioned this in the article. The more you’re going to use a long focal length (e.g.: 300mm or 600mm), the more you’re going to need a high shutter speed to avoid blurred pictures. And who says high shutter speed, always says a very good increase in ISO, especially in low light conditions (dark areas, undergrowth, sunset/sunrise, etc.). If you only shoot with a 14mm, the increase in ISO is less important because you don’t need a high shutter speed. At 500mm, for undergrowth wildlife photography, it’s another story.
About your photography practice
- Don’t hesitate to increase ISO: indeed, cameras today manage ISO sensitivity better and better and you shouldn’t be afraid to push your camera a little in the high ISO range. It’s better to double or triple the ISO than to have a blurry photo, right?
- What type of photo do you shoot: depending on your photographic practice, you will more or less require a significant increase in ISO. If you mainly shoot landscapes in the middle of the day, your interest will be limited. Some undergrowth photography may be useful. In low light conditions, even more. If you also use long focal lengths, the increase in ISO will be important on your body,
- Finally, start thinking about the need to take photos in RAW format rather than JPEG. JPEG is the equivalent of a “raw image”, whereas the JPEG that comes out of your camera has already been processed by your camera. You will therefore have less flexibility to recover colors in dark or overexposed areas. Being able to correctly set the ISO value also allows you to better recover lost elements in the dark or burnt-out (too light) areas of your image.
Conclusion
Although I must admit that this article is very long, I do hope it will be useful for you to understand the concept of ISO sensitivity. If you find anything unclear, please let me know in comments. Want to know more about ISO sensitivity and old metric scales?
In the meantime, I invite you to read my article on the aperture, one of the two other parameters of the famous exposure triangle.
See you soon for the latest article on shutter speed.
I wish you a good learning and beautiful pictures!
Sylvain
