Understanding ISO

ISO was explained to me when I first started as how reactive to light your capturing surface is. The lower the number the less reactive to light it is. The higher the number the more reactive it is.

This isn't exactly true when talking about digital camera's. In a digital camera think of ISO more like a gain control for light. What you are effectively doing when changing your ISO is turning up, or turning down the gain on your sensor.

Just like a radio if you turn the volume right up you'll get distortion. The same goes for ISO, turn it right up and you get noise. If you are shooting in bright daylight, there is no need to have a capturing surface that is super sensitive to light. Therefore, in general you’d go for the lowest ISO you can use while still maintaining the shutter speed and aperture that you want to use.

The above image used ISO 320

At night or in a dimly lit location, you’d want to use a higher ISO to be able to capture more light and use the shutter speeds you are after.

Higher ISO can introduce noise into your images. With the advancements made in digital camera sensors these days I wouldn’t worry much about this.

If you need to use a higher ISO to get the image you want (with the shutter speeds or apertures you want to use), then go right ahead. It’s better to have a little bit of noise in an image than to have no image at all.

Don’t be afraid of using higher ISO’s.