Understanding ISO Settings
In order to fully understand how ISO settings work with digital cameras, I will explain its "history" with film. Remember that all digital cameras are designed after film cameras, and they use the same vocabulary, for the most part, than the traditional analog process.
The I.S.O. is actually a rating given to film that refers to the film’s sensitivity to light. The numerical designation for the I.S.O. works in the following way: the higher the I.S.O. number, the more sensitive the film is to light.
Films with high I.S.O. numbers (above 200) are often called fast films because they can record images quickly and thus need less exposure to light in order to form a successful negative. Films with I.S.O. numbers that are lower than 200 are less sensitive to light.
Films with an I.S.O. of 100 need a flash for most purposes indoors; where as those with an I.S.O. of 400 or more may not. Films that have low I.S.O. numbers are referred to as slow films because they require longer exposure to light in order to record images accurately. The terminology of fast and slow films referring to the I.S.O. explains why the I.S.O. is often called film speed.
Fast films, however, traditionally have a disadvantage: they result in more visual grain than slower films and when enlargements are made the image clarity is somewhat sacrificed. Grain is now often associated with "digital noise" in that when you set the digital camera to a high ISO number, the image will have more noticeable digital noise.
Digital cameras also have ISO designations. The numerical ISO number you designate in your digital camera will mimic its film counterpart. If you set your digital camera to an ISO of 400, the same properties of exposure of 400 ISO film will be created digitally. Your images will, for example, have more visible “grain” and you will be able to set the camera with a faster shutter or a higher f-stop number than if you had set the ISO at 100.
The I.S.O. is actually a rating given to film that refers to the film’s sensitivity to light. The numerical designation for the I.S.O. works in the following way: the higher the I.S.O. number, the more sensitive the film is to light.
Films with high I.S.O. numbers (above 200) are often called fast films because they can record images quickly and thus need less exposure to light in order to form a successful negative. Films with I.S.O. numbers that are lower than 200 are less sensitive to light.
Films with an I.S.O. of 100 need a flash for most purposes indoors; where as those with an I.S.O. of 400 or more may not. Films that have low I.S.O. numbers are referred to as slow films because they require longer exposure to light in order to record images accurately. The terminology of fast and slow films referring to the I.S.O. explains why the I.S.O. is often called film speed.
Fast films, however, traditionally have a disadvantage: they result in more visual grain than slower films and when enlargements are made the image clarity is somewhat sacrificed. Grain is now often associated with "digital noise" in that when you set the digital camera to a high ISO number, the image will have more noticeable digital noise.
Digital cameras also have ISO designations. The numerical ISO number you designate in your digital camera will mimic its film counterpart. If you set your digital camera to an ISO of 400, the same properties of exposure of 400 ISO film will be created digitally. Your images will, for example, have more visible “grain” and you will be able to set the camera with a faster shutter or a higher f-stop number than if you had set the ISO at 100.
Below is a sample of what your Digital SLR ISO Menu Screen Might Look Like
It is important to read your camera manual and know how to set your ISO. Program Modes, Shutter and Aperture Priority Modes, as well as Manual Modes will allow you to select a specific ISO. The great thing about digital cameras is that you are able to change the ISO from one shot to another in order to meet your particular needs. Remember that the ISO affects the exposure, so you can raise or lower the ISO in order to obtain the f-stop/shutter relationship you need for each specific shot.
Camera meters will take into account the ISO you select when reading the light. If you are using a manual meter, you will have to input the ISO setting so that the meter can give you the proper f-stop/shutter choices when it reads the incident light.
Camera meters will take into account the ISO you select when reading the light. If you are using a manual meter, you will have to input the ISO setting so that the meter can give you the proper f-stop/shutter choices when it reads the incident light.