When Does ISO Matter?

Modern cameras have amazing high-ISO capabilities. Back in the days of film, ISO 400 was considered high-ISO by many (including Fujifilm, who designated all their ISO 400 films with the letter “H” for high-speed), and ISO 1600 was ultra-high-ISO, used only out of absolute necessity or by the brave who wanted a certain gritty look. Nowadays some photographers don’t even think of ISO 1600 as a high-ISO setting, and don’t think twice about using it. For many, high-ISO doesn’t really begin until ISO 3200, and ultra-high-ISO doesn’t begin until you go above ISO 6400. It’s really unbelievable!

The real question is this: when does ISO matter? Since modern cameras make such good-looking images at incredibly high sensitivities, when should you start considering image quality degradation? When is a certain ISO setting too high? That’s what I want to answer.

Of course, since this is the Fuji X Weekly blog, I’m discussing Fujifilm X cameras, specifically X-Trans III. This won’t apply 100% to other cameras, but it’s still relevant to some degree no matter the camera make and model. If you are reading this with another camera in mind, take everything said here with a small grain of salt.

I did a little experiment just to better understand all of this ISO stuff. I already knew the answer from experience even before beginning the experiment, but I wanted to see if my instincts matched reality. I captured a few sets of identical pictures, all straight-out-of-camera JPEGs from a Fujifilm X-T20, using ISO 400 and ISO 6400. I made sure that all of the settings were the same between the identical pictures except for ISO and shutter speed. This isn’t 100% scientific, but it’s a controlled-enough test to draw some conclusions about ISO capabilities.

Here are the original pictures:

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ISO 6400

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ISO 400 – my Velvia recipe

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ISO 6400

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ISO 6400

There’s not a lot that can be learned by looking at the above images, other than when viewing images on the web the ISO doesn’t matter whatsoever because it’s incredibly difficult to spot the differences even when comparing side-by-side. In real life nobody does side-by-side comparisons, that’s pretty much an internet-only thing, so it would be impossible to tell if a picture was captured using a low-ISO or high-ISO just by looking at it on your screen. We need to look much closer to really gain anything from this test. Below are some crops from the above images.

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ISO 400

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ISO 6400

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ISO 400

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ISO 6400

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ISO 400

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ISO 6400

If you study the color crops carefully, you’ll notice that the ISO 400 images are cleaner, sharper and have just a hair more dynamic range, but the differences are quite small and subtle. You really have to look carefully to find them. With the black-and-white image, the differences are even less obvious, and I actually prefer the ISO 6400 version, as it seems to have a more film-like quality. Looking at the crops clarifies things a little, but what kind of conclusions can we really draw?

My opinion with regards to color photography and ISO is this: if I’m printing smaller than 16″ x 24″ or displaying the pictures on the web, I don’t find any practical difference between base ISO and ISO 6400. Even ISO 12800 can be acceptable, especially if I’m not going to print the picture. If I’m going to print 16″ x 24″ or larger, a lower ISO is better, preferably less than ISO 3200, but it’s not a big deal to use up to ISO 6400. The ISO that I select does not make a huge difference to the outcome of the image, so I don’t worry a whole lot about it. Put more simply, if I print large, it’s preferable but not critical that I use a lower ISO, and if I don’t print large it doesn’t matter at all.

My opinion with regards to black-and-white photography and ISO is this: the ISO doesn’t matter much at all no matter how large I’m printing, and I often prefer (just by a little) high-ISO over low-ISO because it looks more analog. I freely use without hesitation any ISO up to 12800. Thanks to the Acros film simulation, Fujifilm X cameras are some of the best monochrome cameras on the market, and with that film simulation, often times the higher the ISO the better.

These are, of course, my opinions, and not everyone is going to agree with them, and that’s perfectly alright. Find what works for you. Use a higher ISO or lower ISO if that’s what you need for your pictures, because, after all, they’re your pictures. I’m not here to judge your camera setting choices, only to offer mine, which I’m hoping is helpful to some of you. I hope that this article makes sense and clarifies some things regarding high-ISO on Fujifilm X cameras.

Below is a video that I made on this topic:

The Noise Reduction High-ISO Curve

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Snowfall – South Weber, UT – Fujifilm X-A3 & Jupiter 21M with 2x teleconverter

The noise reduction that Fujifilm applies to their JPEGs increases in strength as the ISO increases. The idea is to get pleasing results at ridiculously high ISOs. This shouldn’t surprise anyone, and I think it is true of all camera brands. I call it the noise reduction high-ISO curve.

Even if you set Noise Reduction to the lowest setting (-4 on my X100F and -2 on my X-A3), the camera is still applying some noise reduction. There’s no way to turn it completely off. I believe even in RAW there is a small amount of noise reduction that’s automatically being applied. As ISO increases, the noise reduction is applied more aggressively.

Digital noise is the modern equivalent of film grain, except that film grain is aesthetically far superior to noise. Fujifilm has programmed their cameras in such a way that the digital noise looks less digital and more analog-esque, and so it is more visually pleasant than what you find with other camera brands. Still, you don’t see very many people purposefully including noise in their photographs because they like the look of it (which you might see with film grain). Instead, most people try to eliminate it as much as practical.

The problem with noise reduction, whether on the camera or via software on a computer, is that it softens the image as a whole. You lose a little crispness. Applying noise reduction becomes a balancing act. Too much noise reduction and the image will look clean but soft, too little and it will look very noisy but crisp.

I don’t mind some digital noise, especially if it’s from a Fujifilm camera because it looks a little more like film grain. I tend to lean more towards sharpness over cleanness. I’ll put up with more digital noise in a black-and-white image than a color image. For monochrome, I typically don’t mind going a stop higher in ISO.

The issue is that pesky noise reduction, which becomes stronger at higher ISOs, and it makes images softer, sometimes too soft. But I’ve found a simple workaround. The picture at the top, Snowfall, was purposefully underexposed by two-stops. I did this so that I could keep the ISO down to where noise reduction isn’t applied so heavily (in this case, ISO 3200). I used the camera’s built-in RAW editor to increase the exposure by two stops, and the results were superior to using the correct ISO (it would have been ISO 12800, which doesn’t look very good on the X-A3).

This isn’t a new idea. I used to do this same technique occasionally on my X-E1. Even on the X100F, it’s better to use ISO 6400 and underexpose one stop, converting the RAW file in-camera and increasing the exposure, than to use ISO 12800 and expose correctly. The difference isn’t dramatic, but there is a difference, as one image will be slightly softer than the other.

Understanding the noise reduction high-ISO curve allows you to make decisions to better achieve desired results when pushing the ISO envelope. It might be better to underexpose and then correct the exposure when converting the RAW file in-camera than to rely on the JPEG with the correct exposure. Perhaps you prefer the way the camera handles noise reduction. It’s all situation specific, and everyone has different tastes. Just know that you have options for handling noise reduction at high-ISO, including underexposure, so as to benefit from a less aggressive noise reduction algorithm.

Fujifilm X100F – Digital Teleconverter + High ISO

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I talked about how the Digital Teleconverter on the Fujifilm X100F adds versatility, and I talked about how great the camera does at high-ISO photography, but I never talked about how these two things do together. I’ve noticed some things about using the Digital Teleconverter at high-ISOs that I’d like to discuss.

Does the Digital Teleconverter limit how high you can go on your ISO settings? The answer is simple: yes. But it’s actually a little bit more complicated than that, so let me dig a little deeper.

I’ve already discussed exactly what the Digital Teleconverter is, and I don’t want to spend much time rehashing that, but basically it’s a digital zoom (zoom-by-cropping) that receives some smart upscaling and sharpening to make the file appear to have more resolution than it actually does. It’s a software trick that allows you to print larger than you might otherwise be able to. You can do this yourself with software on your computer, or you can let the X100F do it for you (which is the Digital Teleconverter).

I’ve also discussed that the practical high-ISO limit on the Fujifilm X100F is 12800, which is very high. Yes, some cameras with larger sensors can go a stop or so higher, but ISO 12800 is way up there, much higher than I ever imagined ISOs going even just 10 years ago.

When using the 50mm Digital Teleconverter (16 megapixel crop) setting, ISO 12800 doesn’t look all that usable. If you want soft and grainy looking black-and-white images, you can get away with ISO 12800 using Acros and the 50mm option. I’ve produced acceptable results this way. However, for the most part, ISO 6400 seems like a more practical high-ISO limit for this situation.

When using the 75mm Digital Teleconverter (12 megapixel crop) setting, anything above ISO 6400 doesn’t look all that usable. ISO 6400 looks alright for soft and grainy looking black-and-white images using Acros. For the most part, ISO 3200 seems like a more practical high-ISO limit for the 75mm Digital Teleconverter.

You might have noticed a trend, and that’s a one stop loss for the 50mm option and a two stop loss for the 75mm option. It’s not that the camera is performing worse, it’s that you are looking much more closely at the exposure (because of the crop). You can more clearly see the degradation in image quality that happens at the higher ISOs. It’s kind of like pixel-peeping–you don’t notice certain things when viewing normally, but they become obvious when you zoom in.

If you use the Digital Teleconverter along with auto-ISO, pay careful attention to the ISO that the camera is selecting. You may need to set it yourself (very quickly and easily done via the knob on top of the camera). My recommendation is to go no higher than ISO 6400 with the 50mm setting and no more than ISO 3200 with the 75mm setting. You can get away with higher sometimes (especially if it’s only for web use), but for best results keep the ISO a little lower than you otherwise would.