Three Reasons Why You Need to Manually Set Your ISO

Written by
Jason Barnette
Posted on
January 10, 2019
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Taking manual control of your camera’s ISO settings can lead to significantly improved photography. Auto ISO settings can often lead to noisy photos or play havoc with your shutter speed. To avoid this, here are three reasons why you need to manually set your ISO.

Part 1: How to Actually Take Manual Control
Part 2: How to Set the ISO Sensitivity
Part 3: How to Set the Shutter Speed (coming January 17)
Part 4: How to Set the Lens Aperture (coming January 24)

The Exposure Triangle

Before we go any further there is one thing you need to understand: The Exposure Triangle. Good photography is all about proper exposure. If a photo is underexposed it looks dark, and if it is overexposed it looks too bright. The Exposure Triangle is a good way of explaining how ISO, shutter speed, and aperture work with one another to create a properly exposed photo.

Take a look at this diagram. Download it. Print it. Memorize it.

The Exposure Triangle showing the relationships between ISO, shutter speed, and aperture.

This diagram shows the different settings for ISO, shutter speed, and aperture and how they affect the exposure in the final image.

You term you will see often in photography is stop of light, or just stops. A stop of light is a relative unit of measurement. Each stop is either half as much light or twice as much light as before. If you were to add a stop of light to your camera settings the photo would be brighter, and vice versa for removing a stop of light.

Snow covered boats beside a lake with dark trees in the background.

When using automatic settings the camera can sometimes be tricked. What do you think the auto ISO setting would have been in a photo with a predominantly dark background?

Understanding ISO

The first thing you need to understand about ISO is that it’s pronounced “aye-es-oh”. It stands for International Standardization Organization which is a group dedicated to creating an international scale for measuring the sensitivity to light for camera sensors.

The ISO scale is a pretty funky thing when you first look at it. Don’t try to make sense out of what the numbers actually mean, just understand that the lowest number is the least sensitive to light and the highest number the most sensitive.

50     100     200     400     800     1600     3200     6400

Each time you increase the ISO number you are adding a stop of light, and each time you decrease the ISO number you are removing a stop of light. This will become more important as you try to get the right exposure for your photos.

To Do: In your camera settings make sure you have your ISO scale set to full stop increments. It is possible to have it set to ½ and 1/3 increments, but if you’re just getting started with learning manual controls you’ll want to make it as easy as possible.

Three Reasons to Manually Set Your ISO

These three reasons will not only make the case for why you should manually set your ISO but also what effect these settings will have on your photography.

1. Gets You Started in the Right Place

Remember how ISO, shutter speed, and aperture all play a role in a properly exposed photo? That means you have three settings you have to think about all the time. At first it will be overwhelming but eventually it will become second nature.

Of all the camera settings for exposure ISO is always the first. Here are a few “rules of thumb” to help you get started with setting your ISO:

ISO 100 – Shooting in snow, on a beach, or near reflective objects like water and glass

ISO 200 – Shooting whites in clothing

ISO 400 – Full sunny day

ISO 800 – Partly cloudy skies or indoors near a window

ISO 1600 – Indoors with overhead lighting such as a gym or restaurant

Now these are just general rules. You may find yourself on a very cloudy day where ISO 800 is still too dark. But these settings will get you started in the right direction.

To Do: Learn how to set your ISO manually in your camera or cellphone. Leave it on manual from now on and select the proper setting for each lighting situation.

A replica of an alligator on display inside an aquarium.

This photo captured at ISO 1600 was extremely noisy in the shadow regions.

2. Reduces Digital Noise

One of the greatest disadvantages of high ISO settings is digital noise. Noise is basically when the ISO is set really high to make the sensor more sensitive to light, but the sensor still can’t really detect that light so it guesses. Often times those guesses are wrong and it results it oddly placed red, green, and blue pixels that creates noise.

When your camera is set to auto ISO the sky is the limit on the setting. Most cameras and cellphones do have a feature to limit how high the ISO can automatically set, though. But if you take manual control of this setting you’ll never have to worry about the automatic setting leading to noisy photos.

Digital noise is worst in the “shadows” of your image. I don’t mean literal shadows, but rather the darkest areas of your photo. This means you should avoid high ISO settings at night and dark interiors. Noise can also lead to less-sharp images if you are capturing portraits.

To Do: Practice setting your camera’s ISO higher until you find the setting that produces an unacceptable amount of noise. Remember that setting and in the future avoid it at all costs.

Stars streaking over a beach with waves in the distance.

If you’re going to shoot on a tripod set the ISO to the lowest setting possible. This photo was captured at ISO 100.

3. Last Setting Before a Tripod is Required

While the ISO is the first setting for getting properly exposed photos it is also the last setting to change before getting a tripod.

During low-light situations such as sunrises and sunsets, indoor shoots, and night photography it may become impossible to shoot a photo handheld. If you lower your shutter speed as far as possible and set your aperture to as wide as possible and still find yourself with an underexposed photo, it’s time to change the ISO setting. Once your ISO setting becomes high enough for noise to become a problem you will know it’s time to use a tripod.

Keep in mind the higher your ISO setting the more noise you’ll have in your final photo. Increase the ISO setting one stop at a time. If you find that your photo is too noisy or still too dark then it is time to break out the tripod for a long exposure.

To Do: If you find yourself using a tripod to capture a long exposure, set your ISO setting to the lowest possible for the least amount of noise.

Next Week

Come back next week as the series continues with Five Rules About Manually Setting Camera Shutter Speed. You can follow the discussion on Twitter with #PhotoTutorialThursday, get daily photo tips on Instagram with #PhotoTipoftheDay, or follow my Facebook Page to get an update.

Feel free to ask questions in the comments below or join the conversation on Facebook or Twitter. I will try my best to answer all your questions. Happy shooting and I’ll see you next week!

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