What Is ISO In Your Digital Camera?

So many people ask the question "what is ISO on my DSLR camera?". Now, if you are old enough to remember the days before this digital era, then you remember going to a photo lab and seeing stacks of film with numbers like 100, 200, and 400 on the boxes (see the picture below).

the ISO numbers on the film roll boxes

This ISO numbers still apply in this digital world. Although, as you'll notice ... twiddling the dial on your camera and you'll get many more numbers now available to you. There's 100, 200, 400, 800, 1600, and so on. The increase of these numbers can be different for each type of camera. And for advanced level camera you can get a wider range of ISO settings.

For our purpose, the ISO numbers to remember are 100, 200, 400, 800, 1600 and 3200. These numbers refer to the sensitivity of the sensor to light. Now, 3200 is more sensitive than 100; so you can take better pictures in low light conditions using this ISO 3200.

The downside is the picture will be very noisy or in film terms will be grainy. In bright sunlight, ISO 3200 would be far too sensitive, and the image will be completely burnt or whited out or over exposure. 100, a low ISO has a low sensitivity to light and make it perfect for a very bright condition like a sunny day.

an example of over exposure image using a high ISO in bright sunlight

So, as a general rule you might want to remember this.

• 100 - bright sunlight
• 200 - cloudy but bright
• 400 and 800 - overcast/shade on bright day
• 1600 - indoor, well-lit room, or dusk

For an entry-level camera, you should avoid the use of ISO 3200 and above, because they are to noisy. You should consider to use a flash in a low light condition.

More advanced cameras will usually be able to solve this noisy image problem at ISO 3200 and ISO 6400.

So, always try to use the lowest ISO that most appropriate every time you take a picture.

Let's look again those numbers. There's an obvious pattern. 200 is double 100, 400 is twice 200, and so on. Now, 100 to 200, or 200 to 400 is know as a stop. Stops work in doubles and halfs; to make sense of it ... here's an example.

You are taking photos on a sunny day; so you have the ISO set to 100. Suddenly, the sun goes behind a cloud. Now, there's roughly half the amount of light hitting your subject and being reflected into your camera to form an image.

If there's half of light; we need to double the ISO to achieve the same exposure. When the sun comes back out and the amount of light doubles; therefore we need the ISO back down 100. Stops in doubles and halfs also apply to shutter speed and aperture.

Assuming the light remains the same; any change in ISO must be compensated by a change either to shutter speed or aperture; in order to achieve the same exposure (same brightness or darkness).

I hope this explanation helps you to understand about the ISO in your camera....