There are really only three camera controls you need to understand – aperture, shutter speed and ISO. This week James Ostinga and Andrew Fildes focus on ISO. In the following weeks we'll look at shutter speed and aperture.
The ISO control changes your camera sensor’s sensitivity to light. As you increase ISO the sensor becomes more sensitive (also referred to as “faster”) so you need less light to make an exposure. Conversely, as ISO decreases the sensor becomes less sensitive, and you need more light to make an exposure.
It’s important to understand that as ISO increases, so too does image noise. Noise, in this context, has nothing to do with the beeping sounds your camera makes when it focuses! Rather, it describes those dots and coloured artefacts you see in some images.
Noise is present in all images, though at low ISO settings it’s usually not visible unless you zoom right in to the smallest details of the image. At high ISO settings it can be so bad it’s a struggle to make out important details – like watching an old TV with bad reception.
The good news is that most DSLRs – even the cheaper models – offer better noise performance than compact cameras. While compacts can get very noisy at 800 ISO, most entry-level DSLRs produce relatively clean images at 3200 ISO. Some high-end pro DSLRs produce great images at 12,800 ISO and beyond.
If you’re shooting outdoors in good light, it’s generally best to use your camera’s lowest ISO setting – 50, 100 or 200 ISO. As the light dims, a higher ISO will help you keep the shutter speed up without the need to add artificial light, such as on-camera flash. Similarly, if you’re shooting sport a higher ISO can help you obtain a faster shutter speed to freeze the action.
The image above was taken at ISO 200 while the image below was shot at ISO 1600.
At print sizes less than A4 it's hard to pick the difference, but zoomed in to over
400%, as is the case here, you can clearly see that image below contains more noise.
Most cameras offer a choice of noise reduction settings – usually low, normal, high and off. You need to think carefully before making a choice here because noise reduction works by softening the image, which reduces noise, but at the expense of image detail. Some cameras do a better job of noise reduction than others so fire off a few high-ISO shots at different noise reduction settings and compare the results on a computer monitor zoomed to 200%.
Many pros leave noise-reduction switched off in camera and use programs such as Lightroom, Capture One, Nik Dfine, Neat Image, Noise Ninja or Photoshop to reduce noise in post-production.
Many pros use programs like Adobe Lightroom (pictured) to reduce noise in post-production. (Image by Mark Galer.)
Article first published in Digital Photography + Design, February-March 2010.