What is Auto ISO and when should you use it?

I’m going to share a secret with you. A lot of the time, I don’t shoot 100% manual. SHHHH!

When learning photography, you hear a lot about the importance of shooting full manual. It gives you full control of your camera and allows you to create the photo you envision.

And that is good advice! Shooting in manual with attention to the exposure triangle will help you create images that become photographs rather than snapshots. Shooting full manual is the sign of a skilled photographer.

So why would you ever not shoot full manual?

Well, sometimes we want to focus on the moment. Every once in a while, we don’t have time to perfect each aspect of the exposure triangle before snapping a shot. Other times, you might want to forget about exposure a bit while you work on a new composition technique. And then there are those times you might need to hand your camera off to your spouse for a shot.

Whatever the reason, there are times when your camera’s Auto ISO sensitivity setting can be very handy!

What is ISO?

ISO refers to the sensitivty of the camera’s sensor (or the sensitivity of film). The higher the ISO, the more sensitive the sensor is to light. The lower the ISO, the less sensitive the sensor is to light.

This means that with the same shutter speed and aperture, a photo in the same light with a higher ISO will be brighter and a photo with a lower ISO will be darker.

More than changing the exposure, ISO also affects image quality. In very simple terms, a higher ISO will result in more grain and lower quality color. By contrast, a lower ISO will result produce less noise, better color, and more detail in the highlights and shadows.

What is Auto ISO?

Auto ISO is a setting that allows your camera to select the appropriate ISO value for each shot based on the parameters you set. You specify the maximum ISO value and metering mode. Then, your camera selects the ISO for each shot based on your shutter speed and aperture.

The Auto ISO option is located in your camera’s ISO sensitivity setting menu. On my Nikon camera, the setting is listed under the shooting settings and is called “Auto ISO sensitivity control.”

To use it, select “on” and specify your maximum sensitivity level. You can set different maximums for flash and non-flash.

Setting-up Auto ISO

It’s important to note that turning on Auto ISO isn’t like switching your camera over to auto mode. You still need to choose your settings carefully for the situation and make choices that will help you achieve your vision.

Choose your shutter speed and aperture. Choose a shutter speed and aperture that fit your situation.

Do you need to freeze motion or blur it? Do you need a wide depth of field, or a nice background blur? Take these variables into account as you adjust your settings.

Set your metering mode. Metering is extremely important with Auto ISO because it controls how your camera will make decisions about the ISO value. You should choose the metering mode you would use if you were shooting fully manual.

Personally, I tend to use spot metering for backlit images and matrix metering for full sun.

Adjust your exposure compensation dial. This is especially important if you intentionally under- or overexpose your images. Exposure compensation tells your camera how bright to make the image. You want it to match how you would normally meter.

I tend to keep exposure compensation dialed down a notch or two when shooting with Auto ISO. I don’t mind some grain in my photos and would much rather have to brighten the photo a bit in post than deal with blown highlights. However, that is a personal preference so just be sure to shoot in a way that matches YOUR style.

Choose your maximum ISO value. Your maximum ISO value might vary based on your setting and the purpose for your photos.

I like grain and don’t like artificial light. So in my personal photos I’ll often let the ISO go as high as 12800. If I’m shooting for clients, I try to keep ISO under 3200 to keep that noise under control.

You’ll also want to keep the lighting situation in mind when setting the max ISO value. If you set the ISO threshold at 3200 but don’t have a good amount of light to work with, your photos may end up underexposed or out of focus from having to compensate using a too slow shutter speed and/or too wide aperture.

When to use Auto ISO

Settings with varied lighting. I have a busy toddler who doesn’t love to follow directions, so I am often chasing after her and photographing her in light that changes frequently.

For example, we have a favorite playground that is half in the shade and half in the full sun. I like to use Auto ISO here because I don’t want to miss a moment or blow out the photo if she runs from one side of the park to the other—as she is likely to do!

In this setting, I’ll usually lock in my shutter speed (usually 1/500 or faster to freeze her motion) and aperture (usually under 2.8 to blur distracting background elements). I turn on Auto ISO, and let her do her thing knowing that I can snap a photo at any time and have a decently exposed image.

Street photography. I take a lot of street photos while out and about with my family. When I’m alone, I have no problem carefully composing a shot, adjusting my settings, and waiting for someone to walk into the frame at the perfect moment. When I’m with family, they don’t usually want to wait around for me!

Using Auto ISO for these strolls allows me to pull up my camera and snap when I see something that interests me, without falling *too* far behind. I can also quickly spin my shutter speed dial down to blur motion, or up to freeze it, and know that the camera will compensate by adjusting the ISO.

Practicing new composition techniques. I’ve been working on incorporating some new composition elements (layering and microcomposing) in my documentary photos. Using the Auto ISO setting has helped me really hone in on the composition of my shots without stressing about the exposure.

Again, I choose my shutter speed and aperture for the situation before I switch Auto ISO on and make sure I have an appropriate metering mode set.

Handing your camera off. We all know it can be super intimidating to hand your giant DSLR off to a family member, friend, or stranger to capture a shot with you in the frame. But it is also SO important to be in the picture every once in a while!

When I have Auto ISO set, I don’t have to worry as much about handing my camera off because I know the camera will handle the metering. It’s still tricky to explain back-button focusing, but at least one hurdle is cleared!

Go for it!

Now you are ready to try it out! Set Auto ISO on your camera. Allow yourself to forget about metering for a little while and focus on the moment. Be sure to share your experiences and tips in the comments!