what is ISO?

In looking back at some of my previous posts, I realized I never did a proper post on ISO. And since ISO is part three of the light trifecta if you will, it's time to give ISO its due.

When referring to film photography, ISO (also called ASA) refers to the film's sensitivity to light. When referring to digital photography, however, ISO refers to the image sensor's sensitivity to light. Many of you may not realize that your digital camera has a function that allows you to adjust your ISO settings. That includes both SLR and point and shoot cameras.

Adjusting ISO can make a big difference in your photos, depending on your lighting conditions. For those of you that hate noise or grain in your photos, or your are shooting in broad daylight, you will want the lowest number ISO settings, such as ISO 100 or 200. If you are shooting in low light conditions or indoors, you will have to bump up your ISO setting to 800 or beyond (unless you are using a tripod).

So why can't you just leave your ISO on auto setting? You can, but you will surely run into lighting conditions that will not be properly exposed unless you change your ISO setting. Remember the exposure triangle concept? (Sorry, I'm about to get all geometric on you...) Picture a triangle with aperture, shutter speed, and ISO at each angle. The goal is to get the correct exposure (a "triangle") every time. But triangles come in all shapes and sizes - the trick is to know how to change the "angles" to make the triangle the size and shape you want. So if your shooting in broad daylight, you can set a higher aperture setting (f/11 and above, let's say), shoot at a fast shutter speed, and use a lower ISO for a super sharp photo. If you are shooting in candlelight indoors, you will have to change your settings: low aperture (f/4 and lower), long shutter speed (below 1/30 of a second), and unless you have a tripod, you will HAVE to increase your ISO setting (ISO 800 or above).

Think of ISO as another play in your exposure playbook. Here's a guide from Bacon Lettuce Photo on the various ISO settings:

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.

I have to admit - I shoot with an ISO 800 and over all the time and I've never noticed a huge problem with grainy photos. But then again, I don't mind noise in my photos... Maybe that's why I've never noticed a huge problem with that?

The beauty of digital is there are several programs out there that can remove noise from your digital photos. So give it a shot - change the ISO and see if it helps.