What Is ISO In Photography?
Setting your ISO is one of three keys to better and creative photos. The other two are your Aperture and Shutter Speed.
But, what exactly is ISO?
Today, you’ll learn what ISO is (and isn’t), a brief history of ISO, and what ISO setting to use in different shooting situations.
Awesome, let’s do it…
Table of Contents
What Is ISO?
In essence, ISO is a camera setting that can increase or darken an image during capture.
Ok, but you’re thinking…
“I don’t shoot film. What does this have to do with my digital camera?”
Well, ISO has been carried over from the film days, and the concept of ISO is similar for digital.
In the digital world, your photos will become brighter, the higher the ISO number. That is if your Aperture and Shutter Speed stays the same.
Therefore, your ISO setting gives you the creative option to choose a different Aperture and/or Shutter Speed based on the available light.
To better understand ISO, we’re going to take a short journey through the days of film. Feel free to skip it if you’re already familiar with the origin of ISO.
Hurter and Driffield – Two scientists from the 19th century standardize the classification of the speed of film at that time (1890’s – 1928)… based on the film’s sensitivity.
Weston – This father and son team had a different method of rating film, and sometimes it conflicted with the manufacturer ratings. This led to confusion on what speed of film you were actually buying.
DIN – This was a competing rating system introduced by the Deutsches Institute Normung. It just added more confusion.
ASA – In 1943, the American Standards Association tried to standardize film ratings by taking inspiration from previous systems and created a new method for rating film.
ISO – In 1974, DIN and ASA were used for inspiration (and were joined) to create a new method to standardize the rating of the film. It’s still used today.
The new ISO standard streamlined the rating system by doubling the film sensitivity based on the numeric value of the film speed. And was adopted by film manufacturers… making it easier for photographers.
Common ISO Settings
Not all cameras will have the exact same ISO settings available.
However, there are some standard ISO settings that most cameras will have.
These are the same ISO ratings we had/have with film.
- ISO 100
- ISO 200
- ISO 400
- ISO 800
- ISO 1600
- ISO 3200
Note: Some cameras will not have an ISO 100 rating. For example, my Nikon D300 does not have it. Nor do some other cameras.
Plus, some cameras have additional options that will be labeled as “HI and “LO”. I find these settings, mainly “HI”, result in poor quality images. So, I try to avoid these and recommend you do the same.
What Do The ISO Numbers Represent?
Rating the sensitivity of film was required, so you knew which one to use during specific lighting conditions.
The same applies to digital photography. Having a number that represents a brightness level, helps in determining which one to use under specific lighting conditions.
In low light situations, you would need a higher (more sensitive) ISO to be able to capture the image with optimal exposure.
For example, a scene lit by candlelight might require a fast (more sensitive) ISO, like 3200.
Shooting at sunset would require maybe 800 or 1600. On a bright sunny day, you may need a less sensitive (slower) film, like 100 or 200.
These are general assumptions. Technically you could shoot at ISO 100 the majority of the time.
As long as you have a tripod so you can shoot at slower shutter speeds and have the lens “wide-open” (larger aperture).
Or if you’re able to increase the amount of light (flash, strobes, etc..), you could then shoot at a lower ISO.
So, numbers were assigned to film based on how sensitive it was to light.
The higher the number, the more sensitive film is.
ISO Doubles Your Light. Sort Of.
You’ll also notice that each ISO number is doubled or halved.
Each time you double the ISO, let’s say from 100 to 200, your camera needs only half as much light for the same exposure.
The opposite is true if you go from 400 to 200… you’ll need twice as much light for the same exposure.
In general, the intensity of the light source is going to be a starting point for what ISO to use.
You’ll also have to take into consideration whether or not you can allow more light to be captured through a larger aperture and/or slower shutter speed.
Depending on the circumstances and your creative vision, you may end up needing a faster ISO.
Where Did ISO Come From and How Do You Pronounce It?
Ask anyone that has been in photography for a while, and you’ll find that most will tell you that ISO is an acronym for; International Standards Organization.
And that you should pronounce it “eye – ess – oh.”
One problem, though. There is no such company called “International Standards Organization.”
Don’t believe me? Google it.
Nothing. Notta. Zilch. It doesn’t exist.
But, there is a company called the “International Organization of Standardization.” Which is not the same as the name above.
Where did “ISO” come from, and why the confusion?
As mentioned previously, there is a company called the “International Organization of Standardization.”
Which is not the same as the “International Standardization Organization.”
From their website…
…the International Organization of Standardization is a non-profit organization based in Geneva, Switzerland.
Their mission is to bring together experts to share knowledge and develop voluntary, consensus-based, market-relevant International Standards that support innovation and provide solutions to global challenges.
However, they made things confusing by adopting “ISO” vs. IOS. Here is a quote from the International Organization for Standardization website…
ISO is their brand! It’s not an acronym. Coke is a brand (which is better than Pepsi, by the way). Not an acronym.
As they mentioned, they use the short form ISO, which is derived from the Greek word isos.
So, ISO is a word.
Pronounced: “Eye-so.” Not I.S.O. (or C.O.K.E.).
Now, here is the real question…
Does It Really Matter?
In the grander scheme of things… no. It’s not going to make you a better photographer.
Truth be told, I’ve been saying “I.S.O.” for 25 years! I had no idea until another photographer informed me of the truth. But, my level of photography didn’t change one way or the other.
Let’s move on…
How ISO is Different in the Digital World
Are the sensors in your camera sensitive to light?
In the analog world, film is sensitive to light. In the digital world, your camera sensor is NOT sensitive to light.
Why “film” is sensitive to light.
Film is made up of different layers. One of which consists of the emulsion. The emulsion is sensitive to light. When exposed to light, an image (of the scene) is “burned” into the emulsion.
For a full scientific explanation, seek out this article from Kodak.
Why the sensor in your camera is NOT sensitive to light.
Our camera’s sensors are made up of electronics. Electronics are not sensitive to light. It gathers the information, from the light, and records it electronically.
For a more technical explanation, check out this post from Wikipedia.
How ISO is Processed by the sensor in your camera
We’ve established that our camera’s sensors are not sensitive to light. Then, the question is, how does ISO affect the brightness of an image?
Two things have to happen with your camera sensor to capture your photo.
…it needs input. That input is the available light from your scene. The light that reaches your sensor is controlled by two things
- Your lens + aperture
- The shutter speed
Your lens funnels the light to your camera body. But, before it reaches the body, it filters through an Aperture (hole in your lens). Then, before reaching your sensor, a shutter has to open to allow the light in.
…your sensor needs to output (record) that information to a media card. This step saves the data the sensor collected and captures your photo.
But, different ISO ratings will alter your final image. Or the brightness of it.
So, how does it make your image brighter or darker if electronics are not sensitive to light? Great question…
The ISO setting you choose will amplify the light during output. The higher the ISO setting, the more the light is amplified. Or the brighter the image becomes.
So if you’re shooting in a low light situation, you can “amplify” the light (during output) with a higher ISO setting.
So adding gain or using a higher ISO doesn’t actually make the camera sensor more sensitive since it’s applied to the output and not the input.
So why the big fuss about accurate and technical information? Is it going to make you a better photographer?
But if you’re an avid music fan, a musician or videographer, then you’re probably already aware of gain. And how it can impact ISO.
Now For The Rest Of Us
Another ISO Advantage Over Film
In the digital world, we are not limited to just 6 ISO’s (100 – 3200).
In fact, a Nikon Z6 has an ISO range of 50 – 51,200!! It even goes higher if you take into account the ability to adjust the EV (exposure value)… all the way up to an ISO equivalent of 204,800!
Oh, and there’s even more. As you manually dial in the ISO, there are smaller increments…
…for example; most digital cameras have the following ISO increments… 100, 125, 160, 200, 250, 320, 400…
These are ⅓, or ½ step increases vs. doubling or halving.
The downside is calculating the settings for aperture or shutter speeds to capture a balanced exposure. It’s easier to figure out if you double or halve the ISO. To compensate, you’ll just double or halve the shutter speed or the aperture.
Cue the calculator. Not!
Luckily, we have a built-in LCD screen to see if our images are over or underexposed. By learning to read the histogram, to capture a balanced exposure, you’ll always be able to nail the exposure in-camera.
If your image is overexposed, drop the ISO to a smaller number. And the opposite if it’s underexposed.
But, you could be there all day until you get it just right. That is, if you’re starting with an ISO, that’s too far from what’s needed.
Coming up, I’ll share some general guidelines on what ISO setting to use in different lighting situations.
So Far, ISO Sounds Like the Perfect Camera Setting. Or Is It?
Although ISO sounds like the perfect camera setting, to achieve your creative vision, it does have one major drawback.
The higher the ISO number you use, the more degraded your image will be. This degradation comes in the form of what is known as the dreaded “Digital Noise.”
Digital noise comes from “amplifying” the light. This “noise” looks like tiny colored pixels in your image.
The first image was shot at an ISO of 100. The second at an ISO of 1600. Notice how the second image looks grittier? That grit is “digital noise.”
Film: With film, the faster (or higher) the ISO, the grainier the image becomes. The grainer the photo the more degraded it becomes.
Here Is Some Good News About Digital Noise
The advancement of technology continues to lower the amount of digital noise created at higher ISO’s.
My first digital camera, a Fuji S2 (in 2002), provided decent photos at ISO 800. Anything faster was useless.
Today, my Nikon Z6 provides me with images I’m happy with at 3200 ISO! That’s a considerable improvement.
Someday, we may not even have to worry about digital noise. Until then, it’s always best to figure out how to shoot at the lowest (acceptable) ISO possible. And how to remove noise in post-processing.
Is ISO Part of The Exposure Equation?
Yes. Yes, it is! Some photographers say it isn’t. Let me explain why it is…
Exposure is how bright or how dark your image is. Both the aperture and shutter speed can be adjusted to determine the exposure. Plus, the ISO can be adjusted for changing the exposure as well!
As you learned earlier, if you go from ISO 800 to ISO 1600, you need half as much light.
But, let’s say you keep your Aperture and Shutter Speed settings the same and shoot at ISO 1600.
The higher ISO is going to amplify the light by (roughly) twice as much. Therefore, your “exposure” is being affected!
In fact, your image is now overexposed. So, ISO does have a direct relation to your exposure.
To “see” this, we can refer to what is known as the Exposure Triangle. On each side, we have one element of the exposure equation: aperture, shutter speed, and ISO.
Your exposure will be brighter with a higher ISO number, slower shutter speed and/or larger aperture. As pictured in the exposure triangle (above).
If you increase the ISO from 100 to 200, then to get the proper exposure, you will need to set a faster shutter speed and/or a smaller aperture.
So, how do you know which exposure setting to select first?
It depends on the available light, whether or not you can manipulate the light and your creative vision for the shot.
That’s a lot to consider.
For now, let’s look at some general guidelines for choosing a specific ISO setting.
Photos During Sunset
At sunset, the intensity of the light begins to fade. The lower to the horizon, the faster the intensity of the light will fade.
Typically, I’ll start with an ISO of around 200 – 400 (depending on the lens, creative settings selected, and intensity of the light). As the intensity fades I’ll increase the ISO accordingly.
Once I reach an ISO of 800, I’ll try and keep it there by shooting with a slower shutter speed and/or larger aperture.
Keep in mind there are other factors that will determine the ISO:
- your lens – a wide-angle allows more light to reach the sensor
- your desired creative choices in regards to shutter speed and aperture
- DSLR vs mirrorless
Photography on a Sunny Day
On sunny days, the light is pretty intense. However, the intensity can change throughout the day, even if it’s sunny all day.
You’ll find the sun to be brightest (most intense) at high noon. Before and after, the light is not as intense. Keep this in mind when shooting outdoors on a sunny day.
So, in general, you can shoot at a very low ISO. Like, 100 or 200. Earlier or later in the day, you may need to start shooting at ISO 400+.
Indoors is a bit trickier. The general rule is, the more intense the light, the lower the ISO you can use.
At home, on a bright sunny day, with lots of windows, you could probably use lower ISO settings. Maybe 200 – 400 would be an excellent place to start.
At home, on a cloudy day, may require a starting ISO of 400+.
At home, at night, with a few lights on will probably require starting at ISO 800+.
Real-World ISO Challenges
The following ISO challenges include three everyday lighting situations you may find yourself in during a photo shoot.
The challenges will also examine how ISO can affect the selection process for the shutter speed and aperture. Plus, why I may choose specific settings based on my creative vision for the shot.
But first, let’s examine how I approach taking photos before I click the shutter release button.
What Camera Settings Should You Select First?
When it comes to setting your ISO, aperture, and shutter speed, you have a lot to consider.
Like, your vision for the shot:
- blurred or sharp background
- freeze the action or
- blur it
- and more
Plus, you have to consider how much light is available.
Are you able to control the amount of light by restricting or adding?
Personally, I like to always start with the camera setting that is going to give me the creative option I want.
So, I’ll either set my shutter speed or aperture first. Then, I’ll adjust the other two camera settings to achieve the desired result.
It’s not always that easy, though. Sometimes, I may end up using a setting I’d prefer not to use. Like, a high ISO of 800+.
Or if I’m shooting on a sunny day, I’ll set the ISO to 100 to start.
Or I could take the easy way out and let my camera make the creative decisions for me. Which would be to put the camera in “auto” mode.
But, if you want creative control over your image, you’ll need to think through what it is you’re trying to achieve.
So, let’s look at how I approach capturing images and how I determine the camera settings for a particular situation.
ISO Challenge 1
For this image, the couple is stationary, and the lighting, although bright, was not that intense.
I had two creative goals in mind for this shot:
One, make sure the surroundings were still recognizable when using a slightly shallow depth of field.
Two, ensure the shot was sharp by avoiding camera-shake.
Due to the lighting situation, I knew a relatively large ISO would be required. So, I started with ISO 800.
Next, I decided on the shutter speed since it was essential to avoid a blurry image. A rule of thumb is to use a shutter speed of at least the size of your lenses focal length. And then double it if possible.
For example, for this image, I was using a 12-24. The longest focal length was 24mm. Therefore, a shutter speed of at least 1/30 of a second would be required.
Although possible, I had a few things going against me.
- it was cold… middle of November in Michigan cold (shivering cold)
- legs were weak due to working 8 hours up to this point
In this case, I quadrupled the focal length for a minimum shutter speed of 1/100th of a sec.
That left me with a decision on the aperture.
Due to the lens, the largest opening (aperture) I could use was f/4. I would have preferred 2.8.
However, because I needed to shoot at a focal length of 14mm (to get this composition), I didn’t have a choice.
So, f/4 it is!
Before setting up the couple, I take a test shot, and… this gives me an image that is underexposed!
To fix an underexposed image requires allowing more light to pass through to the sensor or by amplifying the existing light.
Since I was already at my minimum shutter speed AND largest aperture setting, I only had one choice… increase the ISO (amplify the light).
Luckily, the initial settings were underexposed by 1 stop. By increasing the ISO by 1 stop, I now had a well-balanced exposure with an ISO of… 1600!
ISO Challenge 2
The following day it snows. It’s partly cloudy, and I decide to take some portraits of our son.
My creative vision for this shot is to blur out the background to add separation. And again, ensure the image isn’t blurry due to shivering!
For simplicities sake, let’s say my camera settings are the same as the night before: ISO 1600, f/4, and 1/100th of a sec.
This time I’m using a longer focal length: 85mm. My minimum shutter speed should be 1/200th of a sec.
To blur out the background, I want to use the largest aperture possible. For this lens, it’s 1.4.
Now, to figure out the ISO.
Ideally, the lowest ISO is preferable for the least amount of digital noise. I’m using my Nikon D300s for this shot, and the smallest ISO is 200.
Final settings for test shot: f/1.4 | 1/200 | ISO 200
Result = extremely overexposed!
The camera settings are allowing too much light to reach the sensor. Although it’s a cloudy day, the light is still very intense (bright).
I’ll need to cut down on the amount of light reaching the sensor since it’s overexposed.
Which of the three settings should I adjust to reduce the amount of light being captured?
- If I increase the ISO, it’s only going to amplify the light and create an even more overexposed image.
- Cutting the size of the opening (aperture) down to something smaller could do the trick. However, the increase in depth of field means the background will come into focus.
- Based on my creative vision, my only option is to increase the shutter speed. Which is fine since I need to reduce camera-shake.
The question is, how much should I increase the shutter speed?
While looking through the viewfinder, I adjusted the shutter speed dial until I had a well-balanced exposure (per the light meter).
The final shutter speed = 1/4000th of a sec! This means the initial exposure was 4 stops overexposed.
The weather outside was too frightful! So, it’s time to take our photo sessions inside. Next up, our daughter hamming it up for the camera.
Her play area is situated by a big window that lights up the room. For this photo, I’d prefer natural light vs. any tungsten light. I proceed to turn off the lamps and overhead lighting.
I also want to “freeze” the action. Although she isn’t that fast at this stage, I’d prefer a sharp image.
Another thing I’d like to do is use a relatively shallow depth of field and focus on her face.
Due to the low level of light, I’ll need to use a high ISO. But, I also want to ensure that there’s not a lot of digital noise either.
So, let’s start with ISO 800. Plus, I’m using an 85mm (1.4) lens and decide on f/1.8 for the aperture.
Now, I need to select the shutter speed. Focal length times two gives me a shutter speed of 1/250th of a second.
The test shot showed that the image was overexposed. According to the light meter, it was overexposed by 1 stop.
Changing the shutter speed to 1/500th of a second, provided the desired exposure.
Understanding the relationship between ISO, aperture, and shutter speed are crucial for two reasons:
- It will allow you to take creative control back from your camera and shoot manually
- It ensures you’ll nail the exposure in-camera and won’t have to fix it in editing software
But it’s going to take time + practice. Then, practice some more.
When it comes to selecting your ISO try using the lowest possible setting according to the lighting situation and your creative vision…
- Low-light – sunrise, sunset, stadium lights, and indoors will require a high ISO. Maybe 800+.
- Mid-range – cloudy days or under the shade of a tree. Roughly 400 – 800.
- Intense light – sunny, studio lights, etc. Start at the lowest ISO available on your camera. 100 or 200.
Next, you may want to check out our complete…
Aperture Guide… coming soon
Shutter Speed Guide… coming soon
White Balance Guide… coming soon
If you have any questions about ISO, please post your comments below. Oh, and don’t forget to do the Pop-Quiz!
Thanks for reading and have an awesome day!