ISO – The Simple Explanation!

This is a simple guide to understanding ISO, how it's used 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. Meaning, if your ISO was set to 64,000 you would be able to accurately expose a candle lit dinner. Where as if you were outside on a sunny day your ISO would only need to be set to about 100. So basically the ISO is what the camera uses to measure how much light is hitting the sensor. 

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

Also before the ISO you might have heard of ASA if you ever shot film. It stands for  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.

Also if you want to learn all the crazy nerd details of ISO be sure to check out Film Speed / ISO photography at Wikipedia. 

What does the ISO do?

Besides adjusting your cameras sensitivity to light it also controls how much digital noise you will have on your image. For example, if you set your ISO to 64,000 it's going to be very sensitive to light, but it's going to sacrifice sharpness and add a lot of digital noise. 

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

A few examples of what the different ISO settings look like

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

HIGH ISO setting  in Digital Photography

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

Now lets look at a very low ISO setting. This is set at 100 for this particular photo.

LOW ISO setting  in Digital Photography

You can see there is almost no noise or grain.

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

What I usually like to do is use a tripod when shooting landscapes then slow the shutter down to somewhere around 1 to even 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 will illuminate the scene so there is 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 because you end up capturing a much larger dynamic range of light than you would with compressed Jpegs. So say you were shooting at a 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 cameras ISO in 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.

I almost always shoot at an ISO of 320 when I'm shooting street photography for this very reason. 

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 on where ISO came from, 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 straightfoward. 

Great Youtube ISO video

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.


As always, please like and share below, and if you're interested in more advanced photography tips you can check out my photography tips page.


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