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What the Heck Is ISO and How to Use It

Updated on May 8, 2020
Allenii profile image

Hi everyone my name is Allenii! I've always been an entrepreneur. Today I travel full-time with the dream job of a photographer.

ISO is really not too difficult to understand.

Raise the ISO and the photo will get brighter.

Lower the ISO and the photo will darken.

But what exactly is happening here and why do the photos get grainy if the ISO goes too high?

I like to keep the ISO as low as possible but there are a few scenarios where I purposefully crank up that setting to get a certain look for a photo.

Camera ISO
Camera ISO

ISO is one of those settings where most people know how to use it but don’t understand what's happening internally with the camera.

Well, a common misconception is that ISO is referring to how sensitive the camera sensor is. It’s crazy how many people believe this!

ISO is actually the brightness of the output of the photo. When you crank up the ISO, you’re telling the camera that it needs to brighten up the photo before it gives you the final result.

So when do we use this ISO feature?

I use it in a few scenarios such as low-light, Astro, and vintage style photos.

Here are those scenarios:


Shooting in low light situations can be rather difficult especially when you have no flash or lighting setup. Sometimes, we are forced to bump up the ISO when we have no other options.

For example, I was shooting a wedding in February of 2020. The ceremony was perfectly lit, with windows all around the church, but with the after-party celebration, I was not so lucky. The sun had set and I was trying to capture people dancing but the room was poorly lit with horrible orange lighting and a few laser lights. Unfortunately, my flash was dead and I was stuck shooting with this bad lighting. I lowered my shutter speed to 1/100 (because I was shooting with a 50mm prime F/1.8) and brought the F-Stop down all the way, allowing as much light in as I could.

The photos were still too dark, so I was forced to bump up the ISO to 6400.

The photos turned out a little grainy but nothing I couldn’t fix in Photoshop.

Why do the photos turn out grainy with high ISO?

The reason is really simple. When shooting in low light, the camera sensor is not getting enough light. This means the photo is lacking detail because the sensor can’t capture the objects in the frame.

When bumping up the ISO, you’re telling the camera to brighten up the image even though it doesn’t have all the detail in the shot. The camera then tries to fill in the frame with as much detail as possible, usually resulting in a noisy shot.

It’s simple right?

What other scenarios do we use high ISO?

1. Astro

Taking photos of the stars is going to be difficult with such low lighting.

People take photos of the stars with long exposure. The shutter is usually open for about 30 seconds in order for the sensor to capture enough light.

For these shots, it’s important to raise the ISO to 1600–3200.

This is one of those exceptions where it’s okay to raise the ISO because that’s just how you shoot Astro.

2. Vintage Style

There was one occasion where someone requested vintage style black and white photos. The shoot was at sunset and I really cranked that ISO high to get the grainy look. They actually turned out really cool!

High ISO vs. Low ISO Examples

ISO 1600
ISO 1600
ISO 3200
ISO 3200
ISO 1600
ISO 1600
ISO 1600
ISO 1600
ISO 3200
ISO 3200

Well, that is really it!

ISO is super simple but it’s very important to know when and how to use it.

ISO is just one of the three pillars of shooting manual mode. If you haven’t already checked out the article on F-Stop and Aperture, then I’d highly recommend reading it!

Like always, if you have any questions or want to request an article or my opinion on a subject, either leave a comment or head over to my Instagram :

( @m.allenii )

If you read through this entire post, I’d really appreciate a clap/like.

It boosts my post and helps me reach a larger audience!

Love you all!



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