Photography ISO values

What is photography ISO?

In short, Photography ISO refers to the light sensitivity (or speed) of the film used in a conventional camera or the sensitivity of your image sensor in your digital camera to available light. Together with your  camera aperture settings and shutter speed your ISO settings control the light exposure used to create your photograph.
Film sensitivity means how much light has to hit the film before it has become properly exposed.
For example, it would require twice as much light to expose a piece of ISO 100 film correctly as it would to expose a piece of ISO 200 film correctly.
In the days of film, rather than digital, photographers wanted to know that if they bought a roll of ISO 100 rated film made by Kodak that it would display the same exposure characteristics as a roll of Fuji film also rated at ISO 100. This is where the the "International Organisation for Standardisation" comes in, ISO for short. It sets the criteria that the film companies have to follow so that ISO 100 means the same thing for everyone regardless of the film manufacturer.
ISO is the level of sensitivity of your camera to available light. The lower the ISO number, the less sensitive it is to the light, while a higher ISO number increases the sensitivity of your camera. 
Now in the age of digital cameras it is the "image sensor" inside your camera that is responsible for gathering light and transforming it into an image, With increased sensitivity, your camera is able to capture images in low light situations without the use of a flash. Higher sensitivity however comes at a cost adding pixelization or "noise" to your photo. The higher the sensitivity the greater the risk of noise happening.

ISO setting too high

ISO setting corect

ISO settings too high
ISO settings corect

So what is the correct ISO setting?

Every digital camera has what is known as a "base ISO".  This is your cameras lowest ISO setting where the image sensor will create the highest quality photo without creating any noise.
Photography ISO settings range depending on your cameras image sensor ability. A standard bridge camera may range from ISO 100 to ISO 3200 or similar. Each ISO setting is usually twice the the value of the previous one eg. 100, 200, 400, 800, 1600, 3200 and doubling the sensitivity 
of your image sensor. The lower the ISO setting number the less sensitive your cameras digital image sensor will be to light. The higher the number the more sensitive it will be. There is no standard correct setting as such because you will need different settings for different situations. The general rule of thumb however is to keep your ISO stop setting as small as possible to reduce the risk of noise.

Why use a high ISO stop setting if it's going to create noise?

There will be times when the situation demands that you require a high photography ISO stop setting. For example, if you take a photo at dusk when it is turning dark or on a stormy day when there is very little natural light about. Your photograph will appear dark and under exposed unless you increase your cameras image sensor sensitivity. You do this by turning your camera settings dial to manual "M" and changing the ISO setting there. Most digital cameras will also have selectable pre set ISO stop settings available to suit different environments. These are usually accessed from the scene menu, (SCN on the camera settings dial). These will most likely be shown as night portrait, night scene, twilight or similar. 
For best results always try and use the lowest ISO stop setting you can by altering your cameras aperture and shutter speed to compensate and add light to your exposure.

ISO speed settings

Along with your shutter speed your ISO settings help control how quickly the image sensor creates an image. The below table is a photography ISO setting speed example. This may prove useful to along with your camera shutter speed values when you are trying to capture movement.
  • ISO 100   = 1 second
  • ISO 200   = 1/2 second
  • ISO 400   = 1/4 second
  • ISO 800   = 1/8 second
  • ISO 1600 = 1/32 second
  • ISO 3200 = 1/64 second