ISO
What does ISO stand for?
ISO stands for International Standards Organization, and it is a standardized industry scale for measuring sensitivity to light. This can be used in relation to how sensitive camera film is to light, but more commonly today, it pertains to the sensitivity of a digital image sensor. ISO is measured in numbers, with the lowest number being the least sensitive to light, (e.g. ISO 50 or 100), and the highest number being the most sensitive to light, (e.g. ISO 6400). Almost all digital cameras today allow you some control over your ISO settings, so it is important to know what it is, and what effect it has on your images.
What is ISO
In very basic terms, ISO is simply a camera setting that will brighten or darken a photo. As you increase your ISO number, your photos will grow progressively brighter. For that reason, ISO is a good tool to help you capture images in dark environments or be more flexible about your aperture and shutter speed settings.
However, raising your ISO has consequences. A photo taken at too high of an ISO will show a lot of grain, also known as noise, and might not be usable. So, brightening a photo via ISO is always a trade-off. You should only raise your ISO when you are unable to brighten the photo via shutter speed or aperture instead (for example, if using a longer shutter speed would cause your subject to be blurry).
However, raising your ISO has consequences. A photo taken at too high of an ISO will show a lot of grain, also known as noise, and might not be usable. So, brightening a photo via ISO is always a trade-off. You should only raise your ISO when you are unable to brighten the photo via shutter speed or aperture instead (for example, if using a longer shutter speed would cause your subject to be blurry).
Low vs High ISO Noise Visibility
To give an example of two photos taken at different ISO values, take a look at the comparison below. Pay attention to the level of noise (graininess and blotchy colors) in the images:
When to Use Low ISO
As I have said above, you should always try to stick to the lowest ISO (base ISO) of your camera, which is typically ISO 100 or 200, whenever possible. When there is plenty of light, you should use the lowest ISO to retain the most amount of detail and to have the highest image quality. There are some cases where you might want to use low ISO in dim or dark environments – for example, if you have your camera mounted on a tripod or sitting on a flat, non-moving surface. In that case, bear in mind that your camera will most likely need more time to capture the scene and anything that is moving is probably going to look like a ghost:
As I have said above, you should always try to stick to the lowest ISO (base ISO) of your camera, which is typically ISO 100 or 200, whenever possible. When there is plenty of light, you should use the lowest ISO to retain the most amount of detail and to have the highest image quality. There are some cases where you might want to use low ISO in dim or dark environments – for example, if you have your camera mounted on a tripod or sitting on a flat, non-moving surface. In that case, bear in mind that your camera will most likely need more time to capture the scene and anything that is moving is probably going to look like a ghost:
When to Increase ISO
You should increase the ISO when there is not enough light for the camera to be able to quickly capture an image. Anytime I shoot indoors without a flash, I set my ISO to a higher number to be able to capture the moment without introducing blur to the image. Another case where you might want to increase ISO is when you need to get ultra-fast shots, like the bird picture I posted above. Before increasing the ISO though, you should first decide if it is OK for you to introduce some noise to the image. Remember, the bigger the ISO number, the more noise you will see in your images.
On many of the newer DSLRs, there is a setting for “Auto ISO”, which works great in low-light environments. The beauty of this setting, is that you can set maximum ISO to a certain limit, so when ISO is automatically increased based on the amount of ambient light, it does not cross the set limit. So, if I want to limit the amount of grain in my pictures, I typically set maximum ISO to something like 800 or 1600 on most entry-level cameras and I can push that number even higher on higher-end full-frame cameras.
If you have any questions, comments or feedback, please post them in the comments section below. Please note that the above explanation of ISO is given in very basic/simple terms, similar to film sensitivity. Correctly defining ISO in digital cameras can get fairly complex. If you want to find out more about ISO in digital cameras, including the ISO 12232:2006 standard, please see this article from Wikipedia.
You should increase the ISO when there is not enough light for the camera to be able to quickly capture an image. Anytime I shoot indoors without a flash, I set my ISO to a higher number to be able to capture the moment without introducing blur to the image. Another case where you might want to increase ISO is when you need to get ultra-fast shots, like the bird picture I posted above. Before increasing the ISO though, you should first decide if it is OK for you to introduce some noise to the image. Remember, the bigger the ISO number, the more noise you will see in your images.
On many of the newer DSLRs, there is a setting for “Auto ISO”, which works great in low-light environments. The beauty of this setting, is that you can set maximum ISO to a certain limit, so when ISO is automatically increased based on the amount of ambient light, it does not cross the set limit. So, if I want to limit the amount of grain in my pictures, I typically set maximum ISO to something like 800 or 1600 on most entry-level cameras and I can push that number even higher on higher-end full-frame cameras.
If you have any questions, comments or feedback, please post them in the comments section below. Please note that the above explanation of ISO is given in very basic/simple terms, similar to film sensitivity. Correctly defining ISO in digital cameras can get fairly complex. If you want to find out more about ISO in digital cameras, including the ISO 12232:2006 standard, please see this article from Wikipedia.