7 Auto ISO questions and answers

camera menu iso settingsAuto ISO can be found
under ISO settings.

1. WHAT IS AUTO ISO. That's the first question we'll answer.

This post has a list of questions about this often misunderstood camera setting and I'll give you the right answers about using Auto ISO.

Let's start with a basic review of regular ISO setting. It's the setting you choose on how much light your camera sensor needs for a good exposure. Think of ISO as a scale of how sensitive your camera's sensor is to light.

The following chart gives you an idea of the typical range of ISO settings that are available to you for most DLSR models.

camera ISO chartA low ISO setting means your camera needs more light for a good exposure

You can go into your camera's settings menu and select the ISO you want or you can use the Auto ISO camera setting. Just like it sounds, the definition is that it's the camera setting that enables your camera to pick the ISO setting for you.

Setting your camera's ISO to automatic is a great advantage for you to try in several situations. That helps you pay attention to the other details of taking your photo and not getting caught up in having to adjust your ISO for each photo you take.

Auto ISO Header

You want to improve your photography to more than just a snapshot level and you also want to move past shooting everything in Auto mode. You can play around with trying aperture priority and shutter priority camera settings, but what about setting both the f/stop and the shutter speed and have the camera choose the ISO setting for you?

2. How does iso work with the other camera settings

Intentional motion blur backgroundShutter priority for
intentional motion blur

You can use auto ISO mode with aperture priority, shutter priority, and manual mode.

SHUTTER PRIORITY is the dominant mode to use for sports and action photos where you want to set the shutter speed to freeze the action or get just the right amount of motion blur intentionally.

APERTURE PRIORITY is loved by portrait photographers and landscape photographers who want to control the depth of field.

MANUAL MODE. Wouldn't it be cool to have total creative control and be able to set both the aperture and shutter and get the right exposure in any lighting situation? Well, now you can with Auto ISO.

Aperture PriorityAperture Priority

Shutter PriorityShutter Priority

Shooting with your camera set on Automatic ISO and manual mode will give you the ability to set your shutter speed exactly where you want it to be, combine that with the f/stop that gives you the right amount depth of field you want, and let your camera do the rest.

This is a great thing for you when you are shooting in rapidly or dramatically changing light conditions. Your camera can automatically adjust much faster than you can and still give you the shutter speed and f/stop you want.

Increasing the ISO is really just increasing the amplification of the signal the sensor got during the exposure of the light that was present. Your camera's lowest ISO setting doesn't use any amplification.

3. when is auto iso good?

One good example of when you'd want to use this ISO setting is when photographing birds in flight. They're moving real fast and may fly into shade or sun areas or fly to an area with a different background brightness.

AUTO ISO situationSituation for AUTO ISO

You're looking at maybe a minimum of 1/000 second to freeze the action. You also don't want to shoot wide open at the biggest aperture for fear that you'll miss the focus. You could set the f/stop at f/5.6 or f/8 to give yourself a little latitude in depth of field.

Then you can leave the best ISO setting up to your camera to decide in order to get the exposure right.

4. when is auto iso bad

High ISO noise exampleNoise caused by
high ISO setting

When your camera decides that it needs a extremely high ISO setting to get a good exposure, you'll end up with a loss of quality to some degree.

Super high ISO settings cause your photos to lack sharpness and come out with a lot more digital noise. Digital noise can be described as a grainy look, often with out of place colored pixels.

You can avoid this degradation in quality by limited the maximum ISO in the ISO Range section of your camera's menu system.

How much noise is acceptable is very subjective. I rarely go above ISO with my small sensor point and shoot camera, but go much higher with my full frame sensor camera (up to ISO 2000) and am still happy with the results.

5. How to use Auto ISO in Manual Mode

Nikon and Canon menu listings can be seen in this post and it’s beyond the scope of this post to point to every camera model’s exact location. Refer to your owner’s manual for more information on how to set the Auto ISO maximum.

  1. You first set your camera on manual.
  2. Then set both the shutter speed and set the aperture to the settings you want.
  3. Finally, dial in your ISO to "A" for auto.

You can find your ISO settings somewhere in your camera's menu. It's beyond the scope of this post to provide every camera's exact location. Consult your camera owner's manual for information specific to your camera model.

Your camera will select the needed sensitivity of your sensor to the proper ISO level to get a good exposure. Exposure isn't always perfect. But, just like aperture priority and shutter priority, you can tweak exposure levels if needed with software.

The exposure triangleExposure Triangle

You can use the automatic ISO setting with aperture and shutter priority too, but you give up the control of that component of exposure and the camera's choice likely won't align with your ideas of what you want to do.

6. how can you Adjust The Range You want in Auto ISO?

  1. You can go into your camera's menu and look for "ISO Setting."
  2. Select "ISO Range" and limit the minimum and maximum ISO settings independently.

If you're concerned about image quality at those super high ISO setting you may want to limit the highest ISO in Auto at ISO 1600, rather than the maximum ISO like 25,600. Jump ahead to ISO question #7.

With sophisticated DSLR cameras, you can limit the ISO range.Auto ISO Range Setting

what's The History of Auto ISO?

It's been around since 2004 on Nikon DSLR cameras and Canon followed with this feature on its 7D about 5 years later. Since then, due to the increase in sophistication of digital camera features, auto ISO capability is included on a lot of cameras.

It's only been more recently that it's become more of a topic of discussion on photography blogs and in the world of digital camera talk. There's been an ANTI-AUTO-ISO stigma in the digital photography world for two reasons.

1. AUTO-PHOBIA. Pros and advanced amateurs like us don't want to be accused of using automatic settings. We're control freaks and we want to take control of our camera settings. "Automatic is for amateurs." 

Well, really that's what's great about being able to set your f/stop and shutter speed. You've got the creative say in both of these exposure settings.

2. NOISE-PHOBIA. One of the big limitation in the past was the noise and reduction in image quality at higher ISO settings. Not so anymore. The camera sensor technology and post  image capture processing has dramatically improved. So much in fact, that you can get great quality at high ISO settings.

The justifiable concern for using an amplified higher ISO is becoming almost a non-issue.

Video on Auto ISO

This video is a little lengthy, but it's really worthwhile to watch if you have a few minutes. It covers a lot of good information on this topic. Steve Perry is Nikon shooter, but we won't hold that against him.  ( :-P)

My own Auto ISO Challenge

I've been emotionally stuck on aperture priority mode because of all the portraits I shoot. Portrait photographers like to concentrate control of focus and sharpness on both the subject and the background.

I'm the first one to admit I'm guilty of not venturing out of my comfort zone at times and trying something new. In order to grow as a photographer, I'm leaving my cameras ISO setting on "A."

Does this mean I'll totally convert over to using Auto-ISO entirely? Not likely. Should you switch too? You should give it a try. I think you'll be pleasantly surprised at how much fun it is to set both f/stop and shutter speed.

7. why set ISO to a low number

There are 3 reasons why you may want to use a low ISO camera setting, whether you set it manually or limit your Auto ISO range to just very low numbers.

1. setting iso low for ACHIEVING a slow shutter speed

waterfall blur effectIntentional blur

You want a very slow shutter speed.

This could be because you want a little bit a little bit of blur in your photo, perhaps to create the feeling of motion or speed, or you want that creamy effect when photographing a waterfall.

In brighter situations, even with your lens opening set to its smallest setting, the shutter may have to be fast to get a good exposure and you may want it to be slow for one of the special effects we just mentioned.

2. setting iso low for ACHIEVING a large lens opening (aperture)

You may want to use a large lens aperture to get a shallow depth of field. This is a great way to have your subject in sharp focus, but have the background purposely out of focus.

If your scene is brightly lit, you want your lens sensor to be less sensitive to light so that you can use a wide open lens setting to get a shallow depth of field.

3. highest quality

The most well known reason for using a low ISO setting is to get the highest quality image possible. When your camera is at its lowest ISO setting, you're not amplifying the signal and you will get the best looking image file with good sharpness and without digital noise.


Whether you use Auto ISO or set it manually, sometimes you're forced into jacking that baby up high. Generally, you need a high ISO setting under darker shooting conditions.

1. freeze the action

A higher ISO setting gives you the advantage of being able to use a fast shutter speed to freeze the action because the shutter is open such a shorter time frame. 

This helps you with sports and wildlife photography as well as being able to get sharp pictures without using a flash in dimly lit situations.

2. shoot with high depth of field

If you want both close objects and farther away objects to all be within the range of sharply focused objects, you want a large depth of field. You'll have to use the smallest aperture (lens opening) with a large f/stop number, like f/16 or f/22.

Landscape photographer use small apertures in most of their images because they want both the foreground and the distant background to be in good sharp focus.

3. you can't use flash

When it's too dark and you can't or don't want to use flash you've got to increase the sensitivity of your sensor. You should use Auto ISO or set your camera to high ISO manually.

Taking photos at a rock concert or photographing a basketball game or wrestling match are just 3 examples where flash photography may not be possible. Another example is with night time photography where you aren't using a tripod.

9. When You Shouldn't Use Auto ISO

There are only a few specific instances where setting ISO on auto does not serve you well.

  • When you use flash it won't work properly.
  • When you are controlling the light rather than using existing light, such as when you are shooting photos in a photo studio with strobes or floodlights.
  • When it's super bright you're going to be on your camera's lowest ISO setting (often 100).

In most other situations where you, the creative photographer, wants to have control over shutter speed and aperture, it just makes sense to use it. have a blast playing! If you found this article worthwhile, please share it.

Keep shooting. Keep learning. Keep improving.

Article published by Bruce Lovelace


Bruce is the publisher of Better Digital Photo Tips. Read more on the About Page. He's been known as The Traveling Photographer ever since he started his location photography business in 1994.

View some of Bruce's photos on Instagram.   Visit the Facebook Page. Watch him on YouTube.  Bruce runs photo workshops and provides one on one digital photography coaching.

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