ISO Sensitivity for You and Me

Today’s Post by Joe Farace

ISO (International Standards Organization) ratings are a standard method for quantifying film’s—we’ll get to digital sensors next—sensitivity to light. Lower numbers, such as 50 or 100, represent less sensitivity; while higher numbers, such as 400 or 800, show a film that’s more sensitive.

ISO numbers are proportional to their sensitivity to light. As you double or halve an ISO number, you double or halve film’s sensitivity to light. Film with an 800 ISO is twice as sensitive to light as 400, and 800 film is half as sensitive to light as 1600.

Digital cameras do not have a true ISO speed, which is why you’ll often see the term “ISO Equivalent” tossed around in camera specifications but manufacturers have developed technologies that make your camera’s imaging sensors respond in a manner that’s similar to how film responds to light. Digital cameras typically offer a range of ISO speeds that will vary based on a specific camera’s design but most importantly when you set a digital camera to ISO 400, you can expect a similar response to light than ISO 400 film would produce.

The new Panasonic Lumix G7, for example, offers ISO sensitivities up to 25,600. I am expecting to receive a Lumix G7 for testing real soon now and plan to shoot it at these high ISO settings and show the results up close and personal for you and I to analyze how much noise is there at those levels as well as to find the ISO “sweet spot.”