A Basic Guide to Choosing Your ISO Setting

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?

In this image, my lowest possible ISO setting of 100 in combination with an ND filter allows for a long exposure to blur the water.

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!

In this case, ISO 800 gives me a shutter speed of 1/500. This is enough to freeze the motion of the child, which is exactly what I need.

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.

In this case, an ISO setting of 6400 gives me 1/250. This is enough for me to handhold the camera and still get a sharp image. The noise is not a concern here.

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. 

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Previous comments
Matthias Kirk's picture

Raising the exposure in post is not at all like raising the ISO.
ISO raises the gain of the sensor's analogue light values before it gets converted to a digital signal. The lower the output signal of your sensor, the higher the electronic noise generated further down the processing stream in your camera between the sensor read out and the saving of the raw data.

If you do not believe me set your camera to manual and properly expose for a scene at ISO6400. Then take the same Image with your native ISO and underexposed. In post then raise the exposure of the dark image and compare the results.

The shadows of the low ISO image will be thrashed!

Anonymous's picture

I agree with this! Even though some sensors claim to be ISO invariant, I've found that exposing properly always has the best results.

Francisco Mendoza's picture

Two weeks ago I took a ten years old Xti to a concert, shoot iso 800 (a lot for the camera) with a 17-40mm

Jason Hart's picture

Nicely written Dylan! A good balance of technical considerations without being overly complicated nor watered down.

Matthias Kirk's picture

There are a lot of misconceptions about ISO and noise. ISO does not create noise, too little light does. Actually, with fixed shutter speed and aperture values you get the cleanest image by exposing to the right and raising the ISO as HIGH as possible without clipping highlights. ISO is a photographer's friend and not his enemy.

Anonymous's picture

Very wise answer! ISO does not create noise, it's the lack of light that does (just reiterating haha). If one increases his ISO while increasing his shutter speed, he's cutting out light cos ISO does not affect how much light hits the sensor; the shutter speed does. What I do (as you mentioned) is just to keep my shutter speed and aperture constant, then expose for the shadows with the ISO. It does wonders!

Douglas Neese's picture

I don't know about all DSLR's, but my D800 also has an option of "AUTO ISO". After seeing a video from Steve Perry, he is suggesting to set your shutter and aperture with Auto ISO and see what happens. As time permits, I'm planning on investigating this further.

Anonymous's picture

Auto ISO is a great feature. I would refrain from using it in high contrast scenarios though, as the camera may accidentally over or underexpose.

Douglas Neese's picture

Thanks for the reply....

Fritz Asuro's picture

My general rule to ISO:
Half of the native ISO is the maximum sensitivity you could should with.

CORNEL STAN's picture

"Raising your ISO effectively makes your sensor more sensitive to the light coming in through the lens".
this is a big stupidity ! the photo-diodes generate electric to the amplifiers.Raising ISO is nothing else, raising the gain of amplifiers, more, noise, distortion, narrow the frequency band ( low dynamic range).
Better to get a fast lens. Not good working over 400 ISO if you are professional or wanted a very good quality !

Anonymous's picture

Sorry but I have to disagree with the last statement you made. Yes, higher ISO values can degrade image quality, but that's why many cameras nowadays are designed to handle less than ideal scenarios. If professionals never went above ISO 400, then a lot of masterpieces would not exist today. There are some types of photography that specifically require you to use very high ISOs. Also, sometimes even a fast lens can't help you because shooting a concert (for example) at f/1.2 would result poorly, and even f/2.8 would require you to use ISO values above 1600.