
by Joe
So you wanna know what ISO is? Even if you’ve never heard it, you should definitely know.
In film, ISO, sometimes referred to as ASA or “film speed”, is the films sensitivity to light.
In digital photography, ISO/ASA, is the image sensors sensitivity to light.
I’m going to continue talking about ISO in the context of digital photographer since most of you guys are using digital cameras.
Some basic concepts. The higher the ISO the more sensitive your camera is going to be to light which means you won’t need as much light for the exposure.
Pretend it’s night time. You’re trying to take a picture of a landscape but it’s coming out too dark? Try raising your ISO. Most point and shoot cameras do this automatically.
The trade off to raising your ISO is something called “noise.” On film it’s called “grain” and there is a difference.
If you have ever taken photos on let’s say a camera phone at night you’ll notice that the photo isn’t as clear as it is during the day. That’s because the camera is automatically implementing ISO so that you can take a picture without it being too blurry.
So, the higher the ISO the less light is needed to take a photo.
If I were to take my camera out to the beach on a full and sunny day, I would want my ISO to be as low as possible because I don’t need to amplify the light. If I do, all I’m going to accomplish is a photo with more noise.
Here is a general understanding about ISO setting:
Auto ISO - Ok, you don’t want to mess with it. Let the camera figure it out. BUT, you are not in control. That is NOT how you’re going to become a better photographer.
ISO 100 - Bright light situation. Most times the lowest ISO setting a digital camera offers.
ISO 200 - Cloudy day, overcast. Noise may start showing.
ISO 400 - Indoor photography, maybe sports stop action photos. Most cameras will start showing noise at this point which results in reduced image quality.
ISO 800 and up - Who coughed on the photo and… oh wait. It just looks horrible.
No, I’m just kidding. But most digital cameras will spit out horribly noisy images at this point but some of the more expensive cameras may not.
Different cameras handle ISO and noise differently. I know photos taken on my Nikon D80 with an ISO over 800 tend to start looking horrible. Where as, photos on a significantly more expensive Nikon D3 at ISO 800 look just as clear as ISO 100.
Here I will show you an example, one of my very own images where you can see ISO.
Here is the photo:

You may not be able to see the noise with the image so small so here is a larger, close up version of the top of the photo. Can you see the noise, especially on the right side?

This would be a good opportunity to whip out your camera and play with it. It’s the only way you’re going to get better and play around with the ISO. Try it in different situations and scenarios.
Learn these tools one by one and soon you’ll learn to use them together to create just the image you want. Come back next thursday to learn about exposure.