A Basic Guide to Choosing Your ISO Setting

One feature of our digital cameras that evolves with every single generation of sensors and processors is ISO performance. With astronomical ISO numbers now available, just how high should you push your ISO?

I spoke in my article last week about how most modern cameras have exceptionally good ISO performance and that for most applications, ISO isn’t really something you even need to worry about. Today we’ll take a deeper look into that topic by starting with the positive and negative outcomes of raising your ISO sensitivity. Then, we’ll move on to how far you should raise your ISO. Finally, we’ll take a look at ways of reducing some of the detrimental effects of high ISO on your images. 

Pros and Cons of Raising Your ISO

Raising your ISO effectively makes your sensor more sensitive to the light coming in through the lens. Exactly how this is done varies from sensor to sensor, but there are some common effects that boosting ISO has on the resulting image. 

A sensor with a higher ISO setting will record a given scene more brightly than one with a lower ISO setting. Thus by raising the ISO sensitivity, you are able to achieve higher shutter speeds, deeper depth of field, or both. This can be of great benefit for freezing motion or getting more of a given scene in sharp focus.

There are some trade-offs for this magical ability to record light more brightly, however. These include image noise (which can be ugly or reduce detail), reduced color fidelity, and reduced dynamic range. Typically the higher your ISO setting, the more prominent these effects become. 

So, knowing these things, just how high should you go with your ISO setting?

How High Should You Go?

The Short Answer

The short answer is “as high as you’re comfortable with” or “as high as you need to for the photograph you’re trying to make.” Essentially, it boils down to “it depends,” which isn’t really all that useful. Let’s dig a little deeper.

The Long Answer

Consider Your Final Output

Remembering that noise, reduced color fidelity, and reduced dynamic range are the results of increasing your ISO, will these changes affect your final output? 

Perhaps you’re working for a client who needs an exact color to be represented in the resulting image. In that case, you will probably want to keep your ISO at the sensor’s base ISO to ensure the highest fidelity in your images. 

Another situation where you might want to keep the ISO as low as possible is a scene with a wide dynamic range. An example of this is a landscape scene with deep shadows and also bright highlights. By keeping your ISO at its base setting, you are able to record as much information in the shadows and highlights as your sensor will allow. 

Consider the Scene

One of the benefits of raising your ISO is being able to use faster shutter speeds. So, for example, if you need to freeze action, raising your ISO can be beneficial. It can also help you to avoid camera shake induced by slower shutter speeds when handholding. This is one of the times when I will raise my ISO as high as I need.

It might also be that you need more depth of field. In this case, raising your ISO one or two stops to allow the stopping down of your aperture might be the best solution for your exposure. For example, you may need 1/60 s to freeze the motion of people in your photograph, but not have enough light to do this with the desired depth of field. In this case, raising your ISO is a great solution. 

Personally, I shoot quite a few corporate events in dimly lit rooms. Most of the time, my clients do not want a flash going off because it breaks up the flow of their event. At these events, I routinely shoot at ISO 3,200 or 6,400 on my Fujifilm X-T2 or X-H1. Even though these cameras are considered to be inferior to full frame sensors at these ISO values, they perform well enough for the required output of these events. The client would much prefer to have a slightly noisy image of their VIPs than a blurry one!

Consider Your Subject

As we mentioned earlier, high ISOs can affect color rendition, dynamic range, and detail recording. For subjects such as people, this can have negative consequences. The natural gradation or color of skin can be negatively impacted and fine details such as eyelashes can be lost to noise. It is always important to consider your subject and how important detail and fidelity is.

Which ISO Value Should I Use?

So, all of this is great, but it still boils down to “it depends.” We are a little better informed, but we’re right back to the same problem we started with. So, how can we solve this puzzle?

The one piece of advice that applies to most situations would be to use the lowest ISO value you can get away with. This will produce the highest quality file for a given situation. So, run through the considerations above and then set your ISO as low as you can while still achieving the desired image.

Test Your Camera

Not all sensors are made equal, so it is good to test your camera in your typical shooting situations. This will give you an idea of how far you are personally willing to push your ISO on a photoshoot. For me personally, I don’t mind pushing the Fujifilm X series cameras up to even ISO 12,800 for a corporate event, but I would never do that at a family or couple session unless I really needed to. For those, I would usually stop at ISO 1,600. By that point, the noise introduced reduces the detail too much for my preferences. You might find that with a full-frame camera like the Nikon D850 or the Sony a7 III that you can go much higher and still be happy with the outcome.

How Can I Reduce The Negative Effects?

Two things primarily influence the amount of quality lost due to ISO in our day-to-day photography. Those are the ISO value and the amount of light hitting a given area of the sensor (shadow areas are the first places noise becomes visible and loss of detail is common due to a reduction in dynamic range). With the first, all we can really do is keep the ISO as low as possible. In terms of exposing, we can try to avoid deep shadows by exposing a little brighter than we normally would, or filling in shadows with reflectors, etc. 

In postproduction, we can also use our software's noise reduction features to improve the look of noisy images. Of course, this won't bring back lost color, detail, or dynamic range, but it can make an image appear smoother and more pleasing. 

In Conclusion

Now that we understand more about how changing ISO affects our images and in what situations we might want to raise or lower our ISO, we are better equipped to make decisions on what ISO value to use. The final pieces of the puzzle are your camera and your preferences. How much noise or loss of detail are you willing to accept? Do you really need all the dynamic range your camera offers for the work you do? 

As one final piece of advice, I would suggest that you not consider the effects of ISO on your image unless they adversely affect it. Do not let a little noise or lower dynamic range stop you from making your art. Take the time to understand ISO, master it, but do not let it master you.