what ISO setting should I use

Exposure Triangle, Part 3: Understanding ISO

*Fujifilm X-T30 – ISO 25600 – Ilford HP5 Plus 400 Push Process*

Part 1: Aperture, Part 2: Shutter

As we’ve already discussed, aperture determines the amount of light that enters the camera, and shutter speed determines for how long that light is allowed to expose the camera’s sensor. The third aspect of the exposure triangle is ISO, which is how sensitive the sensor is to that light. Well, that’s not exactly true. ISO works much different with digital sensors than it did with silver halide film, but the basic premise is similar: the higher the ISO, the brighter and “grainer” the image; the lower the ISO, the darker and “cleaner” the image. ISO is found in the camera’s menu, and on some models is controlled by a knob on the top plate or via a wheel around the shutter knob.

This is the simplest of the three exposure triangle elements to grasp, and yet maybe the most difficult. With things like dual-native ISO and ISO invariance, it can be quite confusing. I don’t want to get too deep into the weeds here, because it doesn’t really matter all that much. Basically, Fujifilm cameras technically have just two ISOs: base gain (ISO 200 on X-Trans III and older, ISO 160 on X-Trans IV, ISO 125 on X-Trans V) and second gain (ISO 800 on X-Trans III and older, ISO 640 on X-Trans IV, and ISO 500 on X-Trans V). The base gain is the cleanest of the two. As the ISO is increased from the base gain, the picture becomes “noisier” (a.k.a. “grainier” or “grittier”) because the brightness is being turned up, making the digital noise more obvious. At the second gain point, a switch activates the second base ISO, and the image is actually cleaner than the ISO directly below it. As the ISO is increased from the second gain, it becomes “noisier” because the brightness is being turned up, making the digital noise more obvious. You could photograph at just those two ISOs, and using software increase the brightness, and the results will be the same as increasing the ISO in-camera. Clear as mud?

Another point worth mentioning is that Dynamic Range (DR) and D-Range Priority (DR-P) settings are ISO-dependent. In order to use DR400 or DR-P Strong, the minimum ISO required is ISO 800 on X-Trans III and older, ISO 640 on X-Trans IV, and ISO 500 on X-Trans V. For DR200 or DR-P Weak, the minimum ISOs are 400, 320, and 250, respectively. DR200 and DR400 are unavailable at the extended ISOs. This illustrates another point of confusion: while the maximum dynamic range (range of details between deep shadow and bright highlight) for DR100 is at base ISO, the maximum dynamic range in general is at the second gain point with the camera set to DR400 or DR-P Strong. Confusing, right?

*Fujifilm X-T50 – ISO 51200 – Nostalgic Neg. film simulation*

The old rule of thumb for ISO was to keep it as low as possible, and only increase it when necessary. I think that advice is a little outdated. Fujifilm cameras produce clean results that are very difficult to distinguish from each other at and below the second gain point, and are still pretty clean at and below ISO 1600. Above ISO 1600 the noise becomes more obvious, and it’s up to each person to determine just how high is too high, how much noise is too much noise. Generally speaking, on X-Trans III and newer cameras, I personally find that color photographs are good up to ISO 6400 and black-and-white up to ISO 12800. There are, of course, exceptions to this. You might desire the gritty aesthetic produced by using ultra-high ISOs. Each person’s tastes are different.

Because (for the most part) ISO isn’t all that important, I like to let the camera choose it for me with Auto-ISO. This works with either the Aperture or Shutter set to “A” (Aperture-Priority or Shutter-Priority). In Auto-ISO, the camera will choose the lowest ISO possible, and only increase it when necessary. You can choose the top and bottom ISO values, and the minimum shutter speed. It works really well most of the time. Also, like aperture and shutter, there are full stops (ISO 200, 400, 800 etc.) and intermediate third stops (ISO 250, 320, 500, 640, etc.).

Unless you desire a “grainy” photo, you want to keep the ISO low (however, no lower than the minimum for the Dynamic Range setting used). Find the maximum ISO that you are comfortable with, and set that as the top value of your Auto-ISO (basically, you can set-and-forget). I think a lot of people worry too much about ISO and digital noise—I invite you to try a higher ISO than you might otherwise set as the maximum, as you might find it to be more useful than you previously thought. For the cleanest photographs, keep the ISO low, no higher than the second gain point for your camera.

When Does ISO Matter?

Posted on January 12, 2019 by Ritchie Roesch

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:

ISO 400 – my Ektachrome 100SW recipe

ISO 6400

ISO 400 – my Velvia recipe

ISO 6400

ISO 400 – my Acros Push-Process recipe

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.

ISO 400

ISO 6400

ISO 400

ISO 6400

ISO 400

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: