Is Auto ISO a good idea?

Photographic exposure is dependent upon three variables: aperture, shutter speed and ISO. For photographers shooting film, the aperture and shutter speed might have changed from frame to frame, but ISO was always a constant—at least until you finished the rest of the roll of film (and at 24 or 36 exposures that were usually a ways away).

Skip ahead to digital—and now, not only can you change the shutter speed and aperture with each image, but you can also change the ISO—on the fly—for each image you shoot. This is a great convenience when you’re shooting under constantly changing lighting conditions, such as when you’re going from indoors to outside, or if the sky is partially cloudy or if you’re shooting in the shadows and then going into bright sunlight.

By automating the increase/decrease in ISO, you can focus more on your subject and worry less about the exposure.

Let’s say, for example, that you’re shooting a party and it’s being held both indoors and outside. You may find yourself constantly going from low light to bright sunshine and shady areas outdoors. Rather than manually setting the ISO and shutter speed and aperture every time you walk into a different lighting scenario, you can select the Auto ISO. The Auto ISO feature will automatically adjust the ISO setting to obtain the correct exposure for each new lighting condition. As the lighting diminishes, the camera will continue to increase the ISO until it reaches the “Ceiling” or maximum ISO that you’ve chosen as the highest ISO you’re willing to shoot at. If you need advice on your wedding photography, check out our photography packages and services at Wild Romantic Photography.

Within the Auto ISO settings, you can also set the minimum shutter speed where this “jump” to a higher ISO will occur if you don’t mind hand holding the camera to 1/60 sec. Shutter speed; set that as the minimum shutter speed. Want to minimize the possibility of camera shake—then put the minimum shutter speed to 1/250 sec. The Auto ISO feature tells the camera to change the exposure based on the changing light. As the light in the scene dims, the shutter speed will drop to let in more light to ensure correct orientation. When it hits the “minimum” shutter speed set, the ISO increases to keep the exposure right.

What is Auto ISO?

Auto ISO is a feature common to most digital cameras that allow the camera to pick an ISO for each shot automatically. You can use Auto ISO in Manual, Aperture Priority, or Shutter Priority mode, but it is probably most useful when using Shutter Priority mode. In Shutter Priority, you can pick the optimum shutter speed for your subject and let the camera choose the aperture and ISO.

Is Auto ISO a good idea?

The default for shooting with a combination of Shutter Priority and Auto ISO is for the camera to choose the most effective possible aperture first and then increase ISO as necessary to maintain the desired shutter speed as light levels drop. For most action photography, such as wildlife and people, a shallow depth of field is often selected, but if you need a smaller aperture for more depth of field, consider shooting in Manual mode, which allows you to set both shutter speed and aperture, letting the camera only pick ISO as a floating variable.

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Where Auto Got Its Name

Contrary to popular belief, “Auto” is not short for “Automatic.” “Auto” is the corrupted translation of “Otto,” the first name of Otto Barnack, the smarter older brother of Oskar Barnack, inventor of the first Leica and arguably the father of 35mm photography. Why you didn’t know this is beyond me.

This History of ISO

The term ISO is somewhat of a holdover from the days of analogue film, when you would go to a camera store and buy an entire roll of film with an ASA value of 100, 200, or 400. ASA 200 was twice as sensitive to light as 100, 400 was twice as sharp as 200 (which made it four times as sensitive as 100), and so on. Once the film was loaded into your camera, you could not simply change your mind and use a different value; you had to shoot the entire roll before switching to another ASA for other lighting conditions.

ASA 100 film was great for outdoor situations or other scenarios where there was a lot of light, just like shooting at ISO 100 on a digital camera. ASA 400 was better for indoor conditions when you needed a film that was more sensitive to light if there was not much to work with. If you looked hard enough, you could get a movie that went up to ASA 800 or 1000, but anything beyond that was about as familiar as a Polysepalous bos Taurus (two-headed cow).

I took this photo of a champion marksman on my old D200 at ISO 400. If you look super close at the trees, you will see some noise in the image, but doing that kind of misses the photo’s point.

I took this photo of a champion marksman on my old D200 at ISO 400. If you look super close at the trees, you will see some noise in the image, but doing that kind of misses the photo’s point.

Early digital cameras, not unlike my world-weary Nikon D200, did not offer much in the way of low-light shooting capabilities that their film-based counterparts didn’t already have. Even as recently as a decade ago, if you wanted to shoot in a low-light situation, you might as well grab a roll of high-ASA film since most digital cameras just weren’t very good at their (roughly) equivalent high ISO values. (ISO and ASA are not directly 1:1 equivalent, but the measurements can be treated as reasonably similar for comparison.)

However, all this started to change rapidly as digital sensor technology advanced over the years, and now we are at the point where virtually any consumer camera can shoot up to ISO 3200 or even 6400 (a value that was unheard of with analog film) without much of a penalty in terms of overall colour and luminance noise.

Most digital cameras are so good they can set the ISO automatically (hence the time Auto ISO), essentially removing a critical element of the exposure equation altogether, and freeing you, so you only have to think about aperture and shutter speed.

How Auto ISO Became Cool

Two things had to happen, and both did. First, technological advancements in image sensors and in-camera image processing engines (including noise reduction algorithms) improved so that shots were taken at ISO 1600 and ISO 3200 are perfect. Second, the Auto ISO setting on many cameras features High and Low limits so the user can set a default ISO and the upper ceiling. Some even allow a maximum slow shutter speed threshold as part of the ISO setting so that there’s no need to “worry about blurry.”

This means you can dial in ISO 3200 as the max, ISO 200 as the default and 1/60 sec as the slowest shutter speed, and be confident that my camera is shooting at a low ISO when possible and increasing the gain only when necessary.

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Auto ISO – Controlling Exposure

Using auto ISO can help when a lot is going on, and you don’t have enough time to respond to changing light conditions quickly enough.

ISO controls the sensitivity of your camera’s sensor to light. By changing the ISO, we affect the brightness of the image.

Auto ISO can be used in these shooting modes:

  • aperture priority mode
  • shutter priority mode
  • manual mode
  • program mode

We’ll have a look at how to use auto ISO in the first three shooting modes.

Why Use Auto ISO?

Using auto ISO is an automated way of controlling the brightness of an image. Simultaneously, you can concentrate more on achieving sharp focus, freezing movement, or blurring motion, and getting the depth of field as you’d like it.

Using auto ISO in aperture priority

PRO

As you would normally do with aperture priority, set your aperture, and your camera will set the shutter speed for the correct exposure. The difference with using auto ISO is that you don’t need to place your ISO as well.

As long as you’ve set your maximum ISO and your minimum shutter speed, your camera can adjust the ISO, as well as the shutter speed, to ensure the image is neither too bright nor too dark. When you reach the minimum shutter speed you’ve set, the camera will push the ISO higher.

Your camera’s order of priority when it comes to your settings: 

  • Aperture
  • ISO
  • Shutter

CON 

If you don’t have enough light at your minimum shutter speed and maximum ISO, your camera will use a slower shutter speed than the minimum you have set. It won’t go over the maximum ISO you set.

Using auto ISO in shutter priority

PRO 

As with shutter priority mode, you set the shutter speed, and the camera will use the appropriate aperture for the correct exposure. Again, you don’t need to place your ISO as the camera will also select this.

Your camera’s order of priority when it comes to your exposure settings:

  • Shutter
  • ISO
  • Aperture

CON

As with aperture priority and auto ISO, your image might be too bright or too dark if you don’t keep an eye on what’s happening.

The aperture settings cannot go beyond the capability of your lens. If your lens can only go to F5.6, for example, and you need more light than the maximum possible ISO you’ve set, your image will be underexposed.

The opposite is true; if you want to use a plodding shutter speed that requires a smaller aperture than your lens is capable of or an ISO lower than the minimum ISO of your camera, your photo will be too bright.

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Using auto ISO in manual mode

PRO

In both manual mode and shutter speed priority mode, even after setting your minimum shutter speed under ISO sensitivity settings, you can select your shutter speed as low as you wish.

The minimum shutter speed setting is relevant only in aperture priority and program modes.

CON

If you push your exposure settings, either the shutter speed or the aperture, beyond the minimum ISO or the maximum ISO you set, your image could be too light or too dark, respectively.

When to use auto ISO

It all depends on how you like to work.

Some photographers swear by it and use it all the time. I prefer to do everything manually, but there are circumstances where I would use auto ISO. If the light conditions are changing rapidly, and I don’t have time to keep up with shutter speed, aperture and ISO, I would use auto ISO.

Examples of ideal times to use auto ISO:

  • Sports
  • Rock concert – or any concert or show with changing lights
  • Lifestyle family photography in dense wood with busy children

Is Auto ISO a good idea?

Things to think about when using auto ISO

These days DSLR cameras are capable of so much more at high ISO settings, especially if you have a higher-end camera. If you have an entry-level camera, you need to pay attention to your ISO setting, as a high ISO setting will affect your photos’ quality.

When you use a high ISO:

  • noise increases
  • dynamic range decreases
  • colour accuracy decreases

How you set up your auto ISO settings will help control loss of quality by preventing your camera from using excessively high ISO settings.

Setting up auto ISO

Maximum ISO

Set the maximum ISO that you are comfortable using, rather than leaving it for the camera to go to the absolute maximum it’s capable of using.

Minimum shutter speed

You can set the slowest shutter speed that you are comfortable using. This way, you prevent the possibility of camera shake if your camera selects a shutter speed that is too slow.

ISO sensitivity

Set your ISO sensitivity to what you would ideally like.

Then, when you are in either aperture priority mode or shutter priority mode, your camera will take this into account and adjust the aperture and shutter speed as much as possible to accommodate your ISO setting.

Regardless of whether I use shutter priority mode, aperture priority mode or manual mode, when my aperture and shutter speed settings force the ISO to change from the ISO sensitivity that I set, “Auto ISO” flashes in my viewfinder. This warns me that the ISO is no longer at the sensitivity that I set.

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Problems with using auto ISO

Scenes that are difficult for the camera to meter

You could end up with images that are too light or too dark, as your camera’s exposure meter may be confused by the scene. For example:

  • your camera will want to underexpose a bright background, such as a sunny beach
  • it will want to overexpose a dark background, such as a close up of a black cat

You can use exposure compensation to overcome these difficult situations. Set exposure compensation to plus one or more stops for bright scenes. For dark backgrounds, set your exposure compensation to minus one or more visits.

Auto ISO may be limited.

Your auto ISO setting may limit your camera’s performance in any of the shooting modes, so you could end up with images that are too light or too dark.

Exposure indicator not visible

When using auto ISO in aperture priority or shutter priority, your exposure indicator does not show potential over or underexposure, even if you have reached the ISO setting’s limit.

When Not to Use Auto ISO

Auto ISO is typically not ideal for photography types that don’t involve capturing quick action, such as landscape, architecture, and other types of photography where aperture and depth of field are more important than shutter speed. These types of photography are often conducted in low light, and if you are working with the camera securely on a tripod, you don’t need to worry about having longer exposure times. Auto ISO would try to pick a higher ISO for the low light in such circumstances, introducing unnecessary digital noise, which compromises image quality.

Also, if you are shooting wildlife or action (where you need shallow depth of field) and working in extremely bright conditions, keep an eye on your camera settings, as the camera will select smaller apertures to maintain your chosen shutter speed if it has already chosen the camera’s lowest ISO setting. You might need to increase your shutter speed to use larger apertures or turn off Auto ISO altogether in such circumstances. If you’d like to work with professional photographers for your wedding, book with us at Wild Romantic Photography.

Conclusion

Using Auto ISO is not like wearing a sign that reads, “Clueless Amateur.” Auto ISO can be excellent, too. Maybe it has been all along; Auto ISO is a handy feature when photographing wildlife and action, especially in fast-changing or low light situations.