What is ISO in Digital Cameras?...and When to Change an ISO Setting
The ISO setting in digital cameras is part of the camera's overall exposure system. It is also known as part of what is called the "Exposure Triangle".
In simple terms, exposure is a reference as to whether an image is too light, too dark, or just right according to the photographers preferences.
The three components of the exposure triangle are the ISO setting, the shutter speed setting, and the camera lens aperture setting. Changing any of those settings individually or in combination with the other settings can make an image lighter or darker.
Getting back to ISO, take a look at the two images below.
In simple terms, exposure is a reference as to whether an image is too light, too dark, or just right according to the photographers preferences.
The three components of the exposure triangle are the ISO setting, the shutter speed setting, and the camera lens aperture setting. Changing any of those settings individually or in combination with the other settings can make an image lighter or darker.
Getting back to ISO, take a look at the two images below.
Image #1. ISO 200, F8, 1/600th Sec
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Image #2, ISO 400, F8, 1/600th Sec
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The only camera setting that is different in these 2 pictures is the ISO setting. Picture #1 was taken at ISO 200. It seemed a little underexposed (dark) so picture #2 was taken at ISO 400 and it is the better exposure.
When you set your camera to a higher numbered ISO setting, less light is needed to obtain a "correct" exposure than if the camera is set to a lower ISO number for the same shot. That is important to remember when you are taking pictures in low light settings.
The above example shows how simply changing the ISO setting can be used to lighten or darken an image.
The above example shows how simply changing the ISO setting can be used to lighten or darken an image.
Shown below is an ISO chart listing some of the ISO settings that you can use to adjust the exposure of a picture you are taking. Each larger ISO number will double the brightness of light in an image compared to the lower number next to it. On the other hand, using the next lower ISO number will decrease the brightness of an image by 1/2.
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100 |
200 |
400 |
800 |
1600 |
3200 |
6400 |
12800 |
So, as you can see, the primary reason for changing the ISO is to increase or decrease the brightness of an image. However, the ISO setting is often used in conjunction with the shutter speed and/or lens aperture settings to achieve certain end results in an image.
Those results will usually be the look of motion or blur in an image or how much of the image is in focus from f to back. (depth of field)
Please take a look at Camera Exposure Basics for more on this subject.
Those results will usually be the look of motion or blur in an image or how much of the image is in focus from f to back. (depth of field)
Please take a look at Camera Exposure Basics for more on this subject.
Important to know: Increasing or decreasing the shutter speed or lens aperture settings will allow more, or less light to come through the camera lens and reach the image sensor. Changing those settings will lighten or darken an image.
However, changing the ISO setting does not affect the amount of light that reaches the image sensor through the camera lens. Instead, changing the ISO setting will send an electrical charge to the image sensor that will increase or decrease the brightness of your image that is sent to the camera processor.
It is important to note that changing shutter speed and/or lens aperture setting will allow more or less light to reach the image sensor.
The image sensor collects the light that comes through the camera lens and converts it to an electrical signal. That signal is sent to the camera's processor and ultimately becomes the picture you have just taken. Depending on the camera settings, that picture may be exposed "just right", too dark, or too light.
The image sensor collects the light that comes through the camera lens and converts it to an electrical signal. That signal is sent to the camera's processor and ultimately becomes the picture you have just taken. Depending on the camera settings, that picture may be exposed "just right", too dark, or too light.
Whereas changing your camera's shutter speed or lens aperture setting will allow more, or less light to reach the camera image sensor, (to lighten or darken a picture) the ISO setting works differently.
Changing the ISO setting to a higher or lower setting will boost or decrease the electical signal that gets sent to the camera's processor to ultimately produce a brighter or darker image.
Changing the ISO setting to a higher or lower setting will boost or decrease the electical signal that gets sent to the camera's processor to ultimately produce a brighter or darker image.
Changing your camera's ISO setting will not increase or decrease the amount of light or length of time the light is exposed to the image sensor.
Instead, changing the ISO setting to a higher or lower number will electronically amplify or decrease the amount of light used to produce the final image.
Instead, changing the ISO setting to a higher or lower number will electronically amplify or decrease the amount of light used to produce the final image.
The results of this increase or decrease in the ISO number setting is also referred to as an increase/decrease to the image sensor's "sensitivity" to light.
The Exposure Triangle: As previously mentioned, the ISO setting, camera shutter speed, and lens aperture setting are all part of what is known in photography as the "Exposure Triangle". Those three things work together to produce properly exposed images.
Just as changing the ISO setting can make a picture lighter or darker, the same can be done by changing the shutter speed or lens aperture settings by an equal amount of stops.
As a matter of fact, most photographers will try to adjust exposure more often by changing the shutter speed or lens aperture setting. That is in part because the shutter speed and lens aperture setting can affect other things in the look of the final image besides whether it is too dark or too light. Check the Camera Exposure Basics article for more on the subject.
Just as changing the ISO setting can make a picture lighter or darker, the same can be done by changing the shutter speed or lens aperture settings by an equal amount of stops.
As a matter of fact, most photographers will try to adjust exposure more often by changing the shutter speed or lens aperture setting. That is in part because the shutter speed and lens aperture setting can affect other things in the look of the final image besides whether it is too dark or too light. Check the Camera Exposure Basics article for more on the subject.
Digital Camera Noise/Lower ISO numbers are better:. While it is a great thing to be able to increase your camera's ISO number in order to get the shot you want, there is a down side to doing it. The down side is called "digital camera noise"
The higher your ISO setting, the more noise you may see in your picture. Noise is tiny dots or specks in the image that are generated when a very high ISO number is chosen and the image sensor is amplified to produce a brighter image.
The higher your ISO setting, the more noise you may see in your picture. Noise is tiny dots or specks in the image that are generated when a very high ISO number is chosen and the image sensor is amplified to produce a brighter image.
ISO Image #3, ISO 3200, F 1.8, 1/800 Sec. Shows visible noise
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ISO Image #4, ISO 100, F 1.8, 1/30 Sec. Shows no visible noise.
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Automatic and Manual ISO Settings: When you use your camera in the fully automatic mode, the ISO number may be automatically set for you. The ISO number that the camera chooses will depend upon the amount of available light. It will also depend on any automatic scene mode you have set such as night, sports, or portrait.
In any case, even when a camera is set to an automatic scene mode, it will try to use the best settings for the chosen scene. That will include the most reasonable ISO setting, shutter speed and aperture setting that will produce a well exposed image.
In any case, even when a camera is set to an automatic scene mode, it will try to use the best settings for the chosen scene. That will include the most reasonable ISO setting, shutter speed and aperture setting that will produce a well exposed image.
Images #3 and #4 were taken with a smart phone camera. Upon close inspection, you can see that image #3 is exhibiting the previously mentioned digital camera noise. (especially on the spray container and in the background) That image was taken at ISO 3200 which is a relatively high ISO number. Image #4 was taken with the same camera but does not show the same digital camera noise.
That is because image #4 was taken using ISO 100 and most images taken at a low ISO number like ISO 100 will not exhibit much visible noise.
However, it is important that you realize that all digital images contain some noise. If you were to greatly enlarge image #4 you would begin to see noise in that image as well. However, the noise would not be as much as the noise in image #3.
The good news about digital camera noise is that modern technology has advanced to the point where most cameras can now produce images with minimal amounts of noise. However, please note that cameras with smaller image sensors and pixels like compacts and cell phones will tend to produce images with more noise than Digital Single Lens Reflex cameras and Mirrorless cameras. (which have larger image sensors and pixels}
That is because image #4 was taken using ISO 100 and most images taken at a low ISO number like ISO 100 will not exhibit much visible noise.
However, it is important that you realize that all digital images contain some noise. If you were to greatly enlarge image #4 you would begin to see noise in that image as well. However, the noise would not be as much as the noise in image #3.
The good news about digital camera noise is that modern technology has advanced to the point where most cameras can now produce images with minimal amounts of noise. However, please note that cameras with smaller image sensors and pixels like compacts and cell phones will tend to produce images with more noise than Digital Single Lens Reflex cameras and Mirrorless cameras. (which have larger image sensors and pixels}
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ISO Image #5, ISO 3200, F4.5, 1/250 Sec
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ISO Image #6, ISO 100, F4.5, 1/8 Sec
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As you take a look a pictures #5 and #6 above you may say to yourself that there is no visible difference in the quality of the images. Both were taken with a Digital Single Lens Reflex camera. (at different ISO settings) This reinforces the previous statement that DSLR and Mirrorless cameras with their larger image sensors and pixels will produce images with less visible noise.
Image #5 was taken using ISO 3200 and image #6 was taken using ISO 100. In these days of sending pictures through social media, either image would be fine to send. However, if you have an image that you are going to greatly enlarge and print, an image taken at ISO 100 will exhibit much less noise than one taken at ISO 3200.
In any case, getting a nicely exposed shot with some noise in the picture is better than no picture at all.
When should the ISO setting be changed? Pictures #1 and #2 shown previously in this tutorial are a simple example of how a picture can be made lighter or darker just by changing the ISO setting. That example would apply when the lens aperture setting and the shutter speed setting are not the most important thing in your image.
However, you need to remember that the camera shutter speed and lens aperture setting can affect the look of your final image.
For example: Lets say you are trying to shoot a fast moving subject and your camera is set on ISO 100. Your camera's exposure metering system indicates that a lens aperture setting of F3.5 along with a shutter speed of 1/60 will produce a correctly exposed image.
However, the shutter speed 1/60 second might not be fast enough to "freeze" the action. (moving subjects might be blurred in an image when you are using slower shutter speeds).
The best way to solve the problem is to start by changing your camera setting from ISO 100 to ISO 200. That will decrease the amount of light the camera image sensor will need for a good exposure. You will then be able to increase your shutter speed from 1/60 second to 1/125 second as you attempt to get a properly exposed image.
If that shutter speed isn't fast enough, change from ISO 200 to ISO 400. Then increase the shutter speed to 1/250 second. (let's assume that the shutter speed of 1/250 is fast enough to "freeze" the action). You will then have a nicely exposed image without any blur in it.
Keep in mind that each of the adjustments made to the ISO setting and the shutter speeds in the example above are equal steps/stops. That way, the correct exposure will be maintained.
There also may be times that you might have to change the ISO setting if you want to use a specific lens aperture opening instead of adjusting the shutter speed. The same principle that was just used with the ISO and shutter speed combination can be used the same way with the lens aperture and ISO settings.
In any case, always remember that adjusting the ISO setting may save the day when the shutter speed and aperture settings are not producing the exposure you may want for your image.
So now, the question what is ISO?, has been answered and hopefully you will be able to use this information when making decisions about exposure settings for you images.
Image #5 was taken using ISO 3200 and image #6 was taken using ISO 100. In these days of sending pictures through social media, either image would be fine to send. However, if you have an image that you are going to greatly enlarge and print, an image taken at ISO 100 will exhibit much less noise than one taken at ISO 3200.
In any case, getting a nicely exposed shot with some noise in the picture is better than no picture at all.
When should the ISO setting be changed? Pictures #1 and #2 shown previously in this tutorial are a simple example of how a picture can be made lighter or darker just by changing the ISO setting. That example would apply when the lens aperture setting and the shutter speed setting are not the most important thing in your image.
However, you need to remember that the camera shutter speed and lens aperture setting can affect the look of your final image.
For example: Lets say you are trying to shoot a fast moving subject and your camera is set on ISO 100. Your camera's exposure metering system indicates that a lens aperture setting of F3.5 along with a shutter speed of 1/60 will produce a correctly exposed image.
However, the shutter speed 1/60 second might not be fast enough to "freeze" the action. (moving subjects might be blurred in an image when you are using slower shutter speeds).
The best way to solve the problem is to start by changing your camera setting from ISO 100 to ISO 200. That will decrease the amount of light the camera image sensor will need for a good exposure. You will then be able to increase your shutter speed from 1/60 second to 1/125 second as you attempt to get a properly exposed image.
If that shutter speed isn't fast enough, change from ISO 200 to ISO 400. Then increase the shutter speed to 1/250 second. (let's assume that the shutter speed of 1/250 is fast enough to "freeze" the action). You will then have a nicely exposed image without any blur in it.
Keep in mind that each of the adjustments made to the ISO setting and the shutter speeds in the example above are equal steps/stops. That way, the correct exposure will be maintained.
There also may be times that you might have to change the ISO setting if you want to use a specific lens aperture opening instead of adjusting the shutter speed. The same principle that was just used with the ISO and shutter speed combination can be used the same way with the lens aperture and ISO settings.
In any case, always remember that adjusting the ISO setting may save the day when the shutter speed and aperture settings are not producing the exposure you may want for your image.
So now, the question what is ISO?, has been answered and hopefully you will be able to use this information when making decisions about exposure settings for you images.