A real quick history lesson
Back in the day when cameras were designed to use film, ISO referred to how sensitive a roll of film was to light. Photos shot on a roll of film with a higher iso number would need less light hitting the film to end up with a photo that is properly exposed.
When it comes to modern digital SLR cameras, we no longer use film because it has been replaced by camera sensors, but similar rules still apply. Instead of having different types of camera film that are more and less sensitive, Digital camera’s are able to adjust their sensor ISO setting to act more or less sensitive to light.
The general “Rule of Thumb”
Unlike a camera’s shutter speed or aperture, there is no real creative advantage of changing a camera’s ISO setting.
A general rule of thumb is to always have as low of an ISO setting as possible while still having your photos properly exposed.
The higher the ISO setting, the more you introduce noise into your photos. This is the tiny speckling effect that looks like static in a photo and it is typically avoided as much as possible. On a quick side note, make sure that you do not confuse the photography terms “noise” and “grain”. Although they may seem similar, grain refers to the speckling effect from film photography which is sometimes intentionally added, while noise is only introduced in digital photography and is considered a negative in photos.
How ISO effects the look of your photos
A camera will always take its best photos at what’s called it’s “native ISO” or “base ISO”. For the majority of camera this will be either 50 or 100 ISO. The further away from a camera’s base ISO you get, the more noise will appear in your image.
As much as possible, you want to avoid changing your ISO setting to extremely high digits like 50,000 or what some photographers call “Swiss cheese mode” because the amount of noise will ruin your photos.
Every camera is different depending on their age and sensor, but usually noise will start to become more obvious and distracting at ISO settings over 2,000.
So what is the benefit of adjusting the ISO?
The main purpose of adjusting a camera’s ISO higher is to allow for faster shutter speeds in low light environments. You can think of it as the more sensitive your camera sensor is the quicker you can freeze movement. With that being said, if you are taking photos mid-day or in direct sunlight, there is not much of a reason to set your ISO to anything higher than the Base ISO.
In my next article I’ll talk a little more about the exposure triangle which is the relationship between a cameras aperture, shutter speed and ISO and how they all work together to take a photo! Thanks for reading and be sure to leave a comment if you have any questions!