Photography Basics: ISO

I previous segments I covered the basics of starting out in photography, such as Shutter Speed and Aperture, Lenses and the different functions they perform. Now it’s time to cover a different element that affects your photography: ISO. If you want to learn more about how the ISO on digital cameras works check out my “How Digital Cameras Work: ISO” article.

What is ISO?
If you used film cameras you may already have an idea what ISO is, but it is not quite the same it was in the film days. ISO used to refer to Film Speed, the strength of the sensitivity the film’s emulsion had towards light. The lower the ISO number the less sensitive the film was to light, the higher the number the more sensitive. For example film at 100 ISO would take longer to expose than film at 500 ISO. Although digital cameras do not use film, the concept remains the same. Your ISO is the image sensor’s sensitivity to light. The higher you set your ISO the easier it is to expose an image.

The film sensor of a DSLR camera, where the actual image exposure takes place. Image by ComputerHotline

This may sound endlessly beneficial, but the stronger the ISO the more problems you will have with your photo. This is because of how the ISO on digital cameras work. The higher you set the ISO the more electricity delivered to your image sensor making it more receptive to light, but also interfering with the clarity of that light. This interference is noticeable in most images, and makes the images look grainy. The more and more you turn up the ISO the more grain that will appear in your image.

Using and Setting the ISO
One of the grandest benefits of using a DSLR over a film camera is that you are able to switch your ISO at any time and also have more options for how sensitive you want to make the image sensor. As a general rule you want to set your ISO as low as absolutely possible. The lower you set your ISO the less grain you’ll see in an image. To compensate for the lower or higher ISO you will need to adjust your aperture and shutter speed. While practicing will allow you to best determine the ISO you should use in a given situation, there are a few general guidelines for certain situations.

When you are shooting outside on a sunny day, you should leave your ISO at or below 200 (I sometimes will set it to 250 to use a smaller aperture and faster shutter, however). Typically, on this type of day outside you can shoot almost all photos at 200 ISO, f/8, and 1/250, and make adjustments from there to get the photograph style you want. Using and ISO at or below 200 is virtually always viable if there is some form of sunlight outside.

An outdoor image taken during the daytime requires a very small ISO. Image by cuatrok77

Shooting indoors is where you start to run into complications with setting your ISO. You still want to always try to keep it at or below 200, but unless you are using a studio in which you can control the lighting this may not always be an option. Additionally, you want to try to stay away from the on camera flash as well, since it will create harsh shadows and degrade your image quality. Depending on the lighting situation you may want to increase your ISO. For most indoor shoots you can use and ISO 640 and 800 before you start to deal with large amounts of grain. I strongly recommend that you do not shoot above ISO 800 unless you absolutely have to. Most images you shoot about this ISO will have a very unprofessional quality to them, and rarely come one decent.

Indoors, such as during a concert, is the main time in which you may need a higher ISO. Image by givikat

In the next segment I will cover white balance, what it is, and how to use it.