Is Auto ISO a good idea?

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    Aperture, shutter speed, and ISO are the three factors that determine exposure in a photograph. Photographers using film had to keep the ISO constant no matter what, even if the aperture and shutter speed varied from shot to shot (and at 24 or 36 exposures that were usually a ways away).

    Digital photography has advanced to the point where the ISO can be adjusted mid-shoot in addition to the shutter speed and aperture. This is incredibly helpful when shooting in environments with wildly varying levels of light, such as when transitioning from indoors to outdoors, when the sky is partly cloudy, or when moving from deep shadows to bright sunlight.

    To better focus on your subject without worrying as much about the exposure, you can set your camera to automatically adjust the ISO.

    Assume, for the sake of argument, that you are filming a party that is taking place in both indoor and outdoor locations. You could spend a lot of time outdoors adjusting the brightness of your surroundings. Rather than having to constantly adjust the ISO, shutter speed, and aperture settings on your camera, you can simply turn on Auto ISO whenever you enter a new lighting environment. When shooting in different lighting conditions, the Auto ISO function will automatically set the ISO to the optimal value. You can set a maximum ISO that you are willing to shoot at, and as the light levels drop, the camera will automatically increase the ISO until it reaches that value. If you need advice on your wedding photography, check out our photography packages and services at Wild Romantic Photography.

    Set the minimum shutter speed at which this "jump" to a higher ISO will occur within the Auto ISO settings to 1/60 sec. if you don't mind hand holding the camera. For the shutter speed, that value should be the bare minimum. If you want to take pictures without blurring due to camera shake, 1/250 sec should be your minimum shutter speed. In response to changes in lighting conditions, Auto ISO instructs the camera to automatically adjust the exposure. Shutter speeds slow down as ambient light decreases, allowing more light into the camera and thus preserving orientation. When the "minimum" shutter speed is reached, the ISO must be increased to maintain the correct exposure.

    FAQs About Photography

    What is Auto ISO?

    Most modern digital cameras have a "Auto ISO" setting that lets the camera decide the ISO value automatically. Auto ISO works in Manual, Aperture Priority, and Shutter Priority modes, but it's best suited for Shutter Priority shooting. Select the appropriate shutter speed and let the camera determine the appropriate aperture and ISO in Shutter Priority mode.

    Is Auto ISO a good idea?

    When using Shutter Priority in conjunction with Auto ISO, the camera will select the optimal aperture and then automatically increase the ISO if necessary to maintain the set shutter speed as available light decreases. It is common practise to use a wide aperture when photographing moving subjects like wildlife or people, but if you need a smaller aperture to achieve a greater depth of field, you may want to switch to Manual mode, which gives you full control over shutter speed and aperture while leaving ISO up to the camera.

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    Where Auto Got Its Name

    Many people mistakenly believe that "Auto" is short for "Automatic," but that's not the case. Otto Barnack, the more intelligent older brother of Oskar Barnack, the man widely credited with creating the first Leica and popularising 35mm photography, had his first name corrupted into "Auto," hence the name of the company. It baffles me that you were unaware of this.

    This History of ISO

    The term "ISO" dates back to the days of traditional film photography, when a customer would purchase a full roll of film marked with an ASA rating, such as 100, 200, or 400, at a camera store. For example, the sensitivity of film with an ASA of 200 was double that of film with an ASA of 100, the sensitivity of film with an ASA of 400 was quadruple that of film with an ASA of 100, and so on. Once the film was loaded into the camera, changing the value was not an option; the entire roll had to be used before switching to a different ASA.

    Like shooting with a digital camera set to ISO 100, ASA 100 film performed well in bright environments. When shooting indoors with low lighting, a film with a higher sensitivity rating, such as ASA 400, was preferable. One could find an ASA 800 or 1000 film if one looked hard enough, but anything above that was as common as a Polysepalous bos Taurus (two-headed cow).

    An expert marksman posed for this shot, which we captured with my trusty old D200 and ISO 400. Looking very closely at the trees will reveal some noise in the image, but doing so will cause you to miss the point of the picture.

    With my trusty old D200 and a setting of ISO 400, we captured this portrait of a world-class marksman. You can make out some noise in the image if you look very closely at the trees, but that kind of defeats the purpose of the picture.

    Like my well-traveled Nikon D200, early digital cameras did not improve upon the low-light capabilities of their film-based predecessors in many ways. Prior to the last decade, most digital cameras were not very good at their (roughly equivalent) high ISO values, so if you wanted to take pictures in low light, you might as well grab a roll of high-ASA film. (There is no one-to-one correspondence between ISO and ASA measurements, but they are close enough to be useful for comparison.)

    In contrast, the rapid development of digital sensor technology over the years has allowed for the widespread availability of consumer cameras capable of shooting at ISO 3200 or even 6400 (a value unthinkable with analogue film) with minimal loss of detail in terms of colour and luminance noise.

    Most modern digital cameras are capable of determining the appropriate ISO setting on their own (hence the term "Auto ISO"), freeing you to focus solely on aperture and shutter speed.

    How Auto ISO Became Cool

    Things had to go a certain way, and both of those ways materialised. The first step was the improvement of image sensors and in-camera image processing engines (including noise reduction algorithms), which allowed for perfect shots to be taken at ISO 1600 and ISO 3200. Second, many cameras allow the user to set both a base ISO and an upper limit for Auto ISO. If you're worried about blurriness, some cameras let you set a maximum slow shutter speed threshold as part of the ISO setting.

    Simply setting the maximum ISO to 3200, the default ISO to 200, and the slowest shutter speed to 1/60 sec will ensure that my camera uses a low ISO setting whenever possible and increases the gain only when absolutely necessary.

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    Auto ISO – Controlling Exposure

    When there is too much going on and not enough time to adapt to the changing light, auto ISO can be useful.

    The ISO setting adjusts the light-sensitivity of the camera's sensor. The image's brightness can be adjusted by adjusting the ISO.

    To use Auto ISO, switch to one of these shooting modes:

    • Priority Aperture Mode
    • Priority Shutter Mode
    • "manual mode"
    • system 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 allows the camera to automatically adjust the ISO setting, thus allowing for more precise control over the image's exposure. Focusing on depth of field, motion blur, and freezing action can all be done at the same time, allowing for greater control over each.

    Using auto ISO in aperture priority


    Simply set your aperture as you would in aperture priority mode, and your camera will automatically determine the appropriate shutter speed. The difference with using auto ISO is that you don't need to place your ISO as well.

    When you set a maximum ISO and a minimum shutter speed, your camera will automatically adjust both settings to achieve the ideal exposure. The camera will automatically increase the ISO if the shutter speed you've set as minimum is reached.

    Priority settings for your camera are as follows:

    • Aperture
    • ISO
    • Shutter


    In low-light situations, your camera will use an even lower shutter speed than the one you've set if it has to choose between using a faster one and using a higher ISO. Your maximum ISO setting will be respected.

    Using auto ISO in shutter priority


    You choose the shutter speed, and the camera determines the corresponding aperture to achieve the desired exposure, as in shutter priority mode. Again, the camera will automatically choose the appropriate ISO setting for you.

    The following is a list of the importance of various exposure controls on your camera:

    • Shutter
    • ISO
    • Aperture


    If you're not paying attention while shooting in aperture priority or auto ISO, your image could end up too bright or too dark.

    Your lens's aperture settings are limited by their capabilities. If, for instance, the largest aperture your lens offers is F5.6, but you've set your ISO to its maximum value, your image will be underexposed.

    On the other hand, your photo will be too bright if you use a slow shutter speed that necessitates a smaller aperture than your lens can produce or an ISO lower than the minimum ISO of your camera.

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    Using auto ISO in manual mode


    After establishing a minimum shutter speed in the ISO sensitivity menu, you are still free to choose a shutter speed as slow as you like when shooting in manual mode or with the shutter speed priority setting.

    If you're using aperture priority or programme mode, the minimum shutter speed will actually be used.


    There is a risk of overexposing or underexposing an image if you push the shutter speed or aperture beyond the minimum or maximum ISO you have chosen.

    When to use auto ISO

    It's up to you and how you prefer to get things done.

    As a matter of fact, many photographers routinely rely on it. My personal preference is to always work in manual mode, but there are times when auto ISO is necessary. Auto ISO is what we turn to when we

    don't have time to constantly adjust my shutter speed, aperture, and ISO to account for shifting lighting conditions.

    When it's most appropriate 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

    High ISO performance has improved greatly in modern DSLR cameras, especially those with higher price tags. Using a high ISO setting will degrade the quality of your photos, even if you're using a basic camera.

    With a high ISO setting, you can do the following:

    • The level of background noise is rising.
      the dynamic range narrows
      Reduced colour fidelity

    You can limit the amount of quality decline by preventing your camera from using extremely high ISO settings, and you can do this through the auto ISO settings.

    Setting up auto ISO

    Maximum ISO

    Instead of letting the camera choose the highest ISO possible, set it to a value that's within your comfort zone.

    Minimum shutter speed

    The shutter speed can be set as slowly as you feel comfortable with. You can avoid blurring caused by camera shake when the shutter speed is set manually.

    ISO sensitivity

    Adjust the ISO sensitivity to your prefered setting.

    The camera will then make any necessary adjustments to the aperture and shutter speed in either aperture priority or shutter priority modes to account for the ISO value you have selected.

    When my aperture and shutter speed settings require an ISO sensitivity adjustment beyond what we have set, "Auto ISO" flashes in the viewfinder, regardless of whether we in shutter priority mode, aperture priority mode, or manual mode. This alerts me that the ISO sensitivity has drifted from what we had previously set it to be.

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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:

    • A sunny beach, for example, will cause your camera to underexpose the background.
    • An example would be a close-up of a black cat, where the camera would naturally want to overexpose the background.

    When things get rough, you can use exposure compensation to pull through. Light scenes require exposure compensation of plus one or more stops. Exposure compensation should be lowered by one or more stops when shooting against black backgrounds.

    Auto ISO may be limited.

    Any of the shooting modes could be hindered by the auto ISO setting, leading to overexposed or underexposed photos.

    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

    If you're shooting landscapes, buildings, or anything else where aperture and depth of field are more important than shutter speed, then you probably shouldn't use auto ISO. Low-light photography requires the use of a tripod to ensure the camera remains steady during long exposures; this is especially important if you want to capture fine detail. Low light situations would cause Auto ISO to choose a higher ISO than necessary, leading to blurrier photos due to digital noise.

    Keep an eye on your camera settings if you're working in extremely bright conditions and shooting subjects like wildlife or action (where you need shallow depth of field) because your camera may automatically switch to a smaller aperture in order to maintain your chosen shutter speed if it has already switched to the lowest ISO setting. In these situations, you may need to disable Auto ISO entirely or increase your shutter speed so that you can use larger apertures. If you’d like to work with professional photographers for your wedding, book with us at Wild Romantic Photography.


    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.