What is ISO? A camera's sensitivity to light and how to use it explained


In photography, making sense of some of the jargon can be a daunting task. Understanding
certain terms and how they apply to your camera is key to taking excellent photos. One of
the most confusing settings is ISO, which is one of the three factors of exposure, along with
shutter speed and aperture. Fortunately for you, we’ve put together this simple explanation
to help you better understand what happens when you change your camera’s ISO and how
it will affect your images.

THE BASICS

First, let’s break down the initialize. ISO simply stands for the International Organization of
Standardization, - created in 1987, which is the main governing body that standardizes
sensitivity ratings for camera sensors (among many other things). The term was carried over
from film, when the ISO rating was known as the “film speed”, “ASA” (American Standards
Association), and “DIN” (Deutsche Inclustrie Normen) having a standard of sensitivity is
important, as it allows you to shoot the same ISO on different cameras and trust that the
exposure value will be equal.

HOW ISO IS USED BY CAMERAS

With both analog and digital cameras, ISO refers to the same thing: The light sensitivity of
either the film or imaging sensor. When you change the ISO on a digital camera, you’re
rendering the sensor more or less sensitive to light. One of the greatest features of digital
cameras — one that is often taken for granted — is their ability to change ISO on the fly. In
the days of film, you were essentially stuck with whatever film speed you loaded into your
camera, at least until you finished that particular roll.
Digital cameras typically have ISO settings that range between 100 (low sensitivity) to
12,800 or greater (high sensitivity). Compact cameras and camera phones may top out
below that, however, and some interchangeable lens cameras with larger sensors go even
higher, reaching ISO levels in the hundreds of thousands.

THE EXPOSURE STOPS HERE

Like shutter speed and aperture, ISO values correspond to exposure “stops,” with an
increase of one stop being a doubling of the sensitivity. The relationship of ISO value to
exposure stops is very straightforward: ISO 200 is a one-stop increase (doubling of
sensitivity) over ISO 100. ISO 6,400 is six stops above ISO 100. If you increase ISO from 100

to 400, you need to balance that with a two-stop decrease elsewhere to maintain the same
overall exposure value, say by changing the shutter speed from 1/125 second to 1/500.
Obviously, the e n xact numbers depend on the specific lighting of the situation.

ISO AND QUALITY

Beyond simply changing the exposure, ISO also affects image quality. A higher ISO typically
translates to a noisy or “grainy” image, just as a higher ISO film has more grain than one
with a lower ISO. The picture below showcases how ISO can directly impact image quality,
though; keep in mind that the particular noise levels depend on the camera.


A lower ISO won’t just make less noise, however. It will produce better color and dynamic
range, which is the ability of the camera to capture detail in both highlights and shadows.
Therefore, it is generally recommended to keep ISO as low as possible in order to get the
highest quality output from your camera.

HOW TO CHOOSE ISO



Nonetheless, there are times when it will not be possible to get a proper exposure without
increasing the ISO. The most obvious example of this is low-light scenarios, especially
indoors. Other situations in which you may need a high ISO include instances when you
need to capture action (which requires a fast shutter speed) or deep depth of field (which
requires a small aperture). On cameras with larger sensors, ISO can often be raised quite
high before it starts to significantly impact image quality, so if you’ve got a DSLR or mirror
less camera, don’t be afraid to try a higher ISO if you can’t get the shutter speed or aperture
value you want otherwise.


Here are some common situations that affect how you choose an ISO:

👉 If your subject is moving and you’re trying freeze the motion for a still, a higher
ISO will allow for a faster shutter speed.
👉 If you’re using a tripod to stabilize your camera, you can usually get away with a
slower shutter speed, which in turn allows you to use a lower ISO. Note that a tripod
doesn’t help you freeze subject motion, however. 
👉 If you’re shooting an image that doesn’t require a large depth-of-field, you can
increase the aperture (thus allowing more light into the lens) and use a lower
ISO. Keep in mind that different lenses have different maximum aperture values,
however, meaning not all lenses can let in the same amount of light.
👉 If you’re shooting with artificial light (e.g., a flash) you can typically get away with
a lower ISO setting.
👉 If you plan to only show a small version of an image, such as on Instagram, you can
get away with a higher ISO.
👉 Subjectively, the noise characteristics of a high ISO setting can lend a vintage look to
your photos, although this is an effect that is often better left for post-processing.