Photography Basics: ISO

This week I'm going to delve into one of the terms of photography that you hear and kind of understand, but never really think of when shooting: ISO. ISO stands for the International Standardization Organization and is "the numerical exposure index of a photographic film under the system adopted by the International Standardization organization, used to indicate the light sensitivity of the film's emulsion" (thank you dictionary.com). That definition is a supreme mouthful, so let me help break it down.

ISO is signified by a number (100, 200, 400, 800, etc) that denotes how much light the sensor will take. ISO is a compensation tool, part of the three points of the exposure triangle (aperture and shutter speed are the other two points, but we'll get to those later). The higher the ISO setting, the brighter the picture. Higher ISO's are often used in low light situations. Say you were in your living room watching your two year old play on the couch and it's night time. You (or if you have your camera set on autoISO, then your camera) may bump your ISO up to 800 or higher to get the right amount of light in the sensor to expose the photo properly. Make sense?

 ISO is a way for the computer inside your camera to compensate for the lack of light in any given 
situation. It changes the sensitivity of the camera's sensor so that, even in darker situations, you get a bright and prettily exposed photo.

Here's an example: 

ISO 100

ISO 200

ISO 400

ISO 800

The first picture was shot using ISO 100. The second one was ISO 200, then 400 and then 800. The only setting I changed was the ISO (aperture was f/1.8 and shutterspeed was 1/40 for all four pictures). The first shot is a little underexposed and the last is way too overexposed. ISO 200 seems a tad dark, but the details show up a little better than they do in ISO 400.

Depending on the camera you use, lens, what have you, ISO values can vary. Using my 35 mm, I can achieve an ISO setting of 12800. Some ISO settings can go even higher than that, though I don't recommend going that high for a very good reason: noise level.

Noise in a photo refers to the specks and dots that appear in an image. The camera tries to compensate for the higher levels of light by filling in missing pixels with extraneous information, leading to specks of color and ugliness. The higher your ISO, the more noise or grain is in the picture. Let's look at two more examples:

 ISO 100

ISO 3200

  Look at the top of each picture, right where the brown edging disappears. The brown in the first photo is much clearer than in the second photo. In the second photo, the brown looks a little lighter, a little more degraded. That's the noise (if you click on the image, you can see better what I'm talking about).

It's ultimately up to you what you decide to shoot on in regards to ISO. Sometimes using a higher ISO can't be helped unless you're able to use a flash. I personally try not to shoot with an ISO higher than 800. Past that, the noise becomes noticeable and the picture quality isn't as good (in my opinion). Find the "sweet spot" with your camera and experiment. I'd love to hear about and see your own examples!