ISO – The Simple Explanation!

This is a simple guide to understanding ISO, its use in photography, and the benefits of keeping the number low.

What is ISO in Digital Photography?

In Digital Photography, the ISO is the setting that adjusts how sensitive your camera’s sensor is to light. It usually ranges from 100-64,000+ on most cameras. The higher the number, the less sensitive it is to light. This means that if your ISO was set to 64,000, you could expose a candle-lit dinner accurately. However, if you were outside on a sunny day, your ISO must only be set to about 100. So, the ISO is what the camera uses to measure how much light hits the sensor. 

You might be wondering what ISO stands for. It’s an abbreviation for the International Organization for Standardization. I actually had to memorize that in college and was tested on it in my photography classes. Kind of sad, huh?

Also, before the ISO, if you ever shot film, you might have heard of ASA. It stands for the American Standards Association. I was also tested on that. 

I guess it’s good that it is standardized so all cameras can have the same measurements for light. After all the shutter is standardized by time, the aperture is standardized by Trigonometry. So the ISO or film speed was the only wildcard and some organization decided to standardize what the numbers relate too. Now with the ISO each stop of light equals the ISO number.

What does the ISO do?

Adjusting your camera’s sensitivity to light also controls the amount of digital noise in your image. For example, if you set your ISO to 64,000, your camera will be very sensitive to light, but it will sacrifice sharpness and add a lot of digital noise. 

If you were to shoot at around ISO 100, your images would almost have no noise and be very clean and sharp. This is how I shoot almost all of my landscapes. 

examples of what the different ISO settings look like

The first is an example of the ISO set really high. 

You can see the noise and grain pattern of the sensor standing out. 

Now, let’s look at a very low ISO setting. This is set at 100 for this particular photo.

You can see there is almost no noise or grain.

How do you shoot with a low ISO at night or in the dark?

I usually use a tripod when shooting landscapes and slow the shutter down to 1 to 30 seconds. That way, I don’t sacrifice any image quality and can still soak up all the light with a slow shutter.

The other technique (which usually won’t work for landscape photography) is to use a flash. The flash illuminates the scene, providing enough light for the camera to render images at a low ISO.

Other Digital Photography Tips for Using Your ISO

Always shoot RAW, and the reason for this is that you end up capturing a much larger dynamic range of light than you would with compressed Jpegs. So, say you were shooting at an ISO 100, and all your photos came out too dark. You can adjust your exposure in a post-processing program like Lightroom by simply moving the exposure slider to brighten everything up. This ultimately adjusts your camera’s ISO in the post or in the software. You’ll get more noise the higher you go, but you’ll at least have a workable photo. 

Another good tip in playing it safe that I like to do, is shoot somewhere around an ISO of 320. This way if your photo is over exposed meaning the shots came out too bright, there is a chance that the camera’s sensor was actually only exposed around the ISO rating of 100 so the information can still be recovered in Lightroom by moving the exposure slider to darker.

For this very reason, I almost always shoot at an ISO of 320 when I’m shooting street photography. 

More Resources on ISO

About ISO This is the actualy organizations website.

Photography MAD This one is from Photography Mad. They go into a little history of where ISO came from, including the values, exposure time, noise, etc.

Digital-Photography-School Then of course there is the probloggers photo site Which has a nice simple explanation. I always like their stuff because it’s very clean and straightforward. 

So next time someone asks you, hey Pat, what does the ISO do? or Hey Robin, What is ISO? You can now explain it all to them as I have done to you.