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The GFX 50 Series is an ISO-less Classic

The sensor in the GFX 50 series is certainly not the fastest. Nevertheless, you should not underestimate this ISO-invariant classic with its 50 megapixels. In terms of sharpness and dynamic range, it can still hold a candle to newer developments.

by Rico Pfirstinger

Virtually all cameras of the Fujifilm X series are ISO-less (also known as ISO-invariant). This refers to cameras with sensors for which the ISO setting doesn’t matter in terms of image quality. Only the set aperture and exposure time (shutter speed) are decisive. It’s all about the actual amount of light that reaches the sensor. I have written about this before (German version, English version).

Is My Camera ISO-less?

You can find out yourself to what extent the sensor in your camera is ISO-less. Here’s an example with a GFX 50S: I first shot a consistently lit test subject at f/13, 1/50 sec. and ISO 1600. The result was a correctly exposed image. I then shot the same subject again at aperture 13 and 1/50 sec., but this time I reset the ISO to ISO 100. This is the base ISO value of the GFX 50 series, i.e. its baseline sensitivity. Of course, the second image appears four stops darker. After all, it was taken at an ISO setting that was four stops lower than the first shot, with otherwise the same exposure. To make our second image (captured at ISO 100) appear as bright as the first, we need to boost it four stops in the RAW converter (in our case, that’s Adobe Lightroom). This we do by moving the converter’s exposure slider 4 EV to the right from its zero position.

The same subject shot twice with f/13 and 1/50 sec. – on the left with ISO 1600, on the right with ISO 100 and a subsequent brightening in the RAW converter by 4 EV.

Please click on the image for a larger version.

To better assess whether the GFX 50S used in this example really works ISO-less, let’s take a closer look at enlarged details of the two test shots:

Here we see cropped blowups of our two test shots. Can you tell the difference between the “real” ISO 1600 shot (left) and the ISO 100 image that was subsequently brightened by 4 EV in the RAW converter (right)? No? Then our camera is ISO-less – at least in a range up to 4 EV above base ISO and in combination with Adobe Lightroom. These limitations are important because the RAW converter you use is an integral part of the image processing chain. Not all converters handle drastic brightening equally well. Therefore, every ISO-invariant camera with an ISO-less sensor needs a suitable ISO-less RAW converter that can properly handle the brightening of the RAW data.

Please click on the images for larger versions.

ISO Invariance – the ISO-less Advantage

The RAW files of ISO-less cameras are highly flexible. You can shoot subjects which exhibit an enormous contrast range – for example, a sunset. We first expose the RAW file for the critical highlights using the lowest possible ISO setting (preferably base ISO, i.e. the baseline sensitivity). This results in a shot where shadows and midtones are too dark or literally blocked. We subsequently brighten the dark areas of the image in our RAW converter. The image quality of these brightened areas then largely corresponds with what could have been achieved directly with a higher ISO setting. Such qualitative equality is also referred to as ISO invariance. The great advantage of the subsequent brightening (compared to a shot that was exposed with a higher ISO setting but otherwise the same exposure settings) is the ability to rescue critical highlights.

As we have already seen in the example above, you can easily extend the dynamic range of a shot by four extra f-stops by exposing the GFX 50 to the highlights at base sensitivity (ISO 100) and then brightening the shadow areas that have been lost in the process by up to 4 EV in the RAW converter. You can learn how to do this and how to configure an X or GFX camera for this purpose in my popular Fuji X Secrets RAW workshops.

ISO Invariance – a Practical Example

A typical use case for ISO-less cameras are backlit subjects where bright image areas contrast with much darker areas. Depending on the exposure, either bright areas of the image will blow, or dark areas will be blocked out. With an ISO-invariant camera, we expose such subjects to the critical highlights. This example is a typical sunset, where we want to capture the bright colors around the sun ball.

Of course, you could leave this result as it is. After all, it is quite moody. However, if we want to shed light on the darkness, we have to adjust the tonal values in the RAW converter. Applications such as Lightroom or Capture One provide various sliders to selectively correct the exposure. For example, in this way:

Obviously, we could also brighten dark areas in images from cameras that aren’t ISO-less. However, in doing so, we accept a significantly higher loss of image quality: more noise, more artifacts, less detail, and sometimes even tonal gaps. As a Fuji X user, you don’t have to worry about this, because all X and GFX models released so far work ISO-less, i.e. they are ISO-invariant. Most of the newer models even have two different ISO base sensitivities, the so-called “Dual Conversion Gain” or DCG. This feature can be beneficial in low light. How to practically use DCG and how to determine the DCG level of your own camera is also a topic of my Fuji X Secrets RAW workshops.

  • Click here to go directly to the Flickr album with all the sample images from this article.

Fuji X Secrets Workshops Are Back!

It has been almost a year since I have conducted my last Fuji X Secrets online workshop. After this long break, I’m now back with new online workshops for German-speaking Fujifilm X and GFX series users:

Fuji X Secrets Settings – the ultimate settings workshop for Fujifilm X and GFX

This online workshop will be conducted in German via Zoom. It takes place on September 5, from 2pm to 6:30pm CEST.

Are you looking for the optimal camera settings? Do you want expert explanations why certain settings are beneficial and others aren’t? Then Fuji X Secrets Settings is perfect for you.

Fuji X Secrets Settings is a collaborative online workshop, and it is presented in high-definition via Zoom. This 4-5 hours long workshop will be conducted in German. However, there are plans to also offer this and other Fuji X Secrets workshops in English in the future. Stay tuned!

  • Click here for more information on this workshop.

I also offer a Fuji X Secrets RAW online workshop on September 11:

Fuji X Secrets RAW – better images with Fujifilm X cameras and RAW

This online workshop will be conducted in German via Zoom. It will take place on September 11 from 14:00 to 18:30 CEST.

Fully tailored for Fujifilm users, Fuji X Secrets RAW introduces field-tested tools and procedures for the complete photographic workflow – from the best camera settings and ideal exposure to optimal image processing and output.
  • Click here for more information.

Personal X Tutoring

If you don’t want to wait for English workshops or you’d like to enjoy personalized 1:1 online tutoring that can encompass all Fujifilm-related topics (you choose, mix and match!), you can always book a 1:1 Zoom session in German or English with me. It’s only 60 EUR per hour! If you are interested, please drop me a note.

Fuji X Secrets Books

If you are looking for an in-depth book that helps you making the most of your Fujifilm X or GFX camera, please consider my comprehensive Fuji X Secrets book that pretty much covers all cameras with X-Processor Pro and X-Processor 4:

  • Fuji X Secrets book and eBook, English version: click here. Use code XPERT40 on checkout for a 40% discount!
  • Fuji X Secrets book and eBook, German version: click here.

Disclaimer: With the exception of links to my own products and services, all affiliate links in this article are from and for Fujirumors.