Last Updated on April 8, 2021
As you saw in the photography guide for beginners, ISO is one of the three settings that will effect the exposure of your images. So ISO along with aperture and shutter speed will dictate your exposure making ISO an important concept to understand.
But what exactly is ISO? Just read on for the full ISO guide. Once you understand how to effectively use your ISO you will be well on your way to getting high quality shots.
What is ISO in Photography?
ISO is the abbreviation for International Organization for Standardization. This is an organization that has been around since 1947 and they are from Switzerland.
History of ISO
Throughout the history of photography there have been multiple attempts at setting standards in photographic emulsion. These attempts were to help photographers understand how their film would perform. Today, these various classifications are known as film speed.
In the past film speed was effectively classified in a number of different ways and you very well may run across these terms in your photography career so it is a good idea to be familiar with them. It’s important to understand those that have come before us!
Hurter and Driffield: The standard created by these two was used all the way up until 1928. Their system was based on an inverse system of film classification. Therefore the higher the HD number the lower the exposure and emulsion that was needed.
GOST: This was the standard used in the Soviet Union from 1928 until 1951. This system is the eastern version of the ASA system you will see shortly.
DIN: This German system was introduced in 1934 and it utilized degrees in order to classify.
ASA: The American Standards Association was instituted in 1943 and uses a linear scale. This system was still in use all the way up until 1988 when ISO was instituted.
ISO: ISO is based on combining DIN and ASA systems. In this system the doubling of a films sensitivity is denoted by a doubling of the film speed. This tells you how sensitive to light your film is.
What Does ISO Actually Mean?
Now you know that ISO is a way of noting a films speed and it’s light sensitivity.
When looking at ISO numbers it is important to remember that a lower ISO number means that there is less light sensitivity which means more light is necessary to attain proper image exposure. Therefore, a higher ISO number means there is a higher light sensitivity. Now exposure requires less light will be needed.
In film there are specific ISO numbers you will see. They are 50, 100, 200, 400, 800, 1600, 3200. These numbers are doubled going up and halved when going down the scale. This means that it takes twice as much light for exposure at 50 than at 100. That also means that using an film with an ISO of 200 needs half as much light as using an ISO 100 film.
The numbers used to measure ISO in film is also used in digital photography. In the case of digital ISO the number denotes the sensitivity of the image sensor. The primary difference in ISO numbers in digital photography compared to that of film is that the ISO numbers can go significantly higher. You will also find ISO stops in increments of 1/3 between the standard film ISO numbers. This adds lighting adjustment versatility over what can be achieved in film.
It is important to remember that when shooting in digital a lower ISO number means there will be less noise in your images. This means a higher quality image. But also remember that a higher ISO means adjustments must be made to your aperture and shutter speed which an lead to a balancing act in achieving your desired effect.
ISO’s Effect on Exposure
Because ISO is based upon how much light you are letting in to the image sensor, it has a large impact on exposure. Most photographers are attempting to shoot with the lowest possible ISO as it provides the best image quality the lower the setting is. This progressively minimizes noise and image grain. But the ISO you end up using has multiple factors needed to be considered.
Therefore the shooting environment should dictate how you set your ISO to achieve proper exposure. For example, if you are shooting in high light conditions like those found outside on a summer day then a low ISO of 100 is likely correct. If you are shooting inside where there is less light then you will then raise your ISO setting. This could be as high as 1600 or more.
Because exposure is dictated by ISO, aperture, and shutter speed you will need to be proficient at balancing all three settings for proper exposure. Let’s show you an example to make the concept more concrete because once you have this down you will be able to effectively shoot under all lighting conditions.
Let’s say that you are shooting in a medium light situation and have your ISO set to 400. You would likely have your aperture set to f/16 and a shutter speed set at 1/400. But what if you wanted to shrink your depth of field?
First you would lower your aperture setting to f/8, which is two stops. To maintain the same exposure as your previous settings you will have to adjust your ISO by an increase of two stops. You could also increase your shutter speed by two stops.
Does Increasing Your ISO Brighten Your Photo?
You should be thinking about ISO in terms of how much light is in your environment, not necessarily about how bright your images are. ISO is about allowing the correct amount of light into your sensor to achieve the exposure you are seeking.
So it is important to remember that as you raise your ISO the amount of light in your environment should be higher. If you are lower your ISO it should be due to there being less light in the environment.
Adjusting brightness of an image is a better way to look at post processing that you can do in a photo software such as Adobe Lightroom. The software does not change the ISO but you can raise and lower the brightness of your image. It is a good idea to understand the difference to avoid confusion as you move forward as a photographer.
Another way to look at it is that ISO deals with the highlights of an image while brightness is handled post shooting and it refers to the tones across the entire image.
ISO and Exposure Explained
As noted above, ISO plays a huge role in exposure. It is important to know that both ISO and shutter speed effect exposure at the same scale. Meaning that an equal change in either setting will have a comparable effect on exposure.
Therefore, if you have a lower ISO you will get a low exposure and a higher ISO will provide a high exposure. Aperture’s effect on exposure is not as clean and you can learn more about that in the aperture guide.
How ISO Effects Image Quality
When looking at the ISO setting just remember that a lower number means a higher image quality while a higher number means your image will have more noise.
Digital noise is less clarity and more grain in your image. So when you double the ISO number you are also doubling the image grain. As grain goes up your image detail and clarity goes down.
So why would you use a higher ISO? When shooting in low light conditions you will often need a higher ISO setting. When shooting in low light you will have to understand your ISO settings in order to balance light with image quality.
The other ways to allow more light in while keeping your ISO low is by lowering your shutter speed or widening your aperture. It is important to note that a slower shutter speed will create motion blur in your image so if this is not the desired effect you will not want to slow your shutter speed. A wide enough aperture also may not be an option depending on your lens. This is what makes these three settings an art that feels like a juggling act.
So as you lower your ISO setting you are decreasing the amount of lights that reaches your sensor. Let’s say you step your ISO down to 100 from 6400. That is six stops down so to get the same exposure level you will have to lower your shutter speed or your aperture. To do so with your shutter speed it will have to slowed six stops down to 1/2.
But a one half second shutter speed will definitely create motion blur when shooting a moving subject. This may not be the desired effect such as when shooting a concert for example.
The best way to remember ISO is that a lower number equals lower light sensitivity which leads to better image quality.
Remember that the higher your ISO number is the more image grain you will have. Usually the goal is to shoot with the lowest ISO number possible.
One of the best ways to achieve lower ISO number is shooting with a full frame camera. The larger image sensor size of these cameras allows you to shoot in a lower ISO setting than you can with a crop sensor under the same conditions.
What ISO Setting To Use
Daylight: When shooting in bright outside lighting you should shoot with an ISO of 100-200.
Indoor: For most indoor lighting conditions an ISO of 200-400 should be utilized.
Indoor with Flash: If you are using a flash then set your ISO to 400-800. This will give you a better exposure and background detail than the standard indoor ISO setting.
Event Photography: For most events such as concerts in relatively low light conditions you will shoot with an ISO of 800-1600.
Low Light Events: Some events will have very low light available. For these situations you will want to set your ISO to 1600-3200. In these situations you may have to use a tripod in order to shoot with a low enough shutter speed.
Very Low Light Environments: If you find yourself shooting at night or any other extremely low light situation then you will have to crank the ISO up to 3200 or more. Unless you specialize in night photography or night street photography, you will likely not run into this that often.
ISO Setting for Low Light Photography
The exact ISO setting for shooting in low lighting varies depending on the quality of your camera sensor. Higher end full frame cameras perform better than entry level crop sensor models when shooting in low lighting.
There are also cameras out there that are specifically designed for shooting in low light. And if being a night photographer is your goal you will be well served to invest in one of these cameras. To see the recommended models read the best camera for night photography article.
As a general rule, older DSLR cameras will not handle low light as well as modern models. There is obviously exceptions to this rule. As an older full frame camera very well may outperform a newer crop sensor camera.
When setting your ISO for low light situations you will want to set your ISO after aperture has been set. For an in depth night photography setting guide check the article.
But as a quick primer, set your aperture two stops down from it’s widest setting. Then set your shutter speed so that it is now larger than your lens’s focal length. For example, if you are shooting with a 50mm lens then you will want to set your shutter speed to 1/60. You will then set your ISO to 1600. It may need to be adjusted a stop up or down. This will allow you to have a larger focal length while still getting enough light for proper exposure.
Landscape Photography ISO Settings
Unless you are trying to shoot landscapes at dusk or night, then you will always want to shoot landscapes with an ISO of 100.
Daylight allows you excellent lighting meaning you can use the lowest possible ISO setting. This will provide you with noise free, high quality images. High resolution images are very important in landscape photography. Read the full landscape photography settings guide for more info.