When testing cameras, it is not unusual to see a situation when one camera can produce results a bit darker or brighter than another. In some cases, lenses are to blame for this variance, since most lenses cannot ideally transmit all of the incoming light. What this means, is that a lens with a maximum aperture of f/2.8 could potentially transmit less light, which could be equivalent to say f/3.5 in terms of brightness. The latter number is what is often referred to as a “T-stop”, or Transmission-stop, which is basically an adjusted f-stop that takes into account this light loss. In other cases, the camera itself can be the source of brightness variance. Although manufacturers are supposed to adhere to an ISO standard that guides the process of determining the right brightness level for each ISO, there is usually still some variance between not only brands, but also between specific camera models. We won’t get into the question of why there are such variances. Instead, we will concentrate on implications of such variances to camera sensor comparisons and ratings. Particularly, we will be looking at exposure variances in Fuji cameras, such as the Fuji X-T1. Many photographers, including myself, have been fond of the way Fuji sensors render images, outputting very clean and pleasant-looking images, even at high ISOs. But are those ISOs real? And is Fuji doing something shady to make its images look better? Let’s take a closer look…
When testing cameras, I am pretty open about showing what camera settings I use for a particular scene. Knowing that light can have a huge impact on the scene and also knowing that the same source of light is practically never perfectly constant in brightness, particularly over a long period of time, I always retest every camera that I provide in comparisons. This way, you are not looking at a scene captured a year ago from one camera and the same scene captured a week ago from another camera. This process takes a long time, but I don’t mind doing it, as I want to only show our readers a more accurate representation of true sensor performance. Due to the above-mentioned variances, making a fair comparison between cameras proved to be rather difficult. How do we compare cameras? Do we compare them at the same ISOs at identical exposure levels? Do we compare them at the same ISOs, but at different exposure levels to match the same brightness? Do we compare them at the same brightness at equivalent ISOs? Or perhaps we should compare them at the same ISOs, but make further adjustments in post-processing to match brightness levels? As you can see, making the proper decision on comparisons is no easy task. So far, I have been comparing sensors based on the same ISO level, but making exposure adjustments to match the same brightness across different cameras. While this method works fine to show differences in noise levels at the same ISOs, differences in exposure can yield to potential issues for such comparisons, as we are not necessarily looking at an apples-to-apples comparison, particularly when variances in exposure are very high.
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Fuji X-T1 vs Sony A7 II
Let’s take a look at a rather typical situation involving a Fuji camera (in this case the Fuji X-T1) and the Sony A7 II (Left: Fuji X-T1, Right: Sony A7 II):
The Fuji X-T1 had the Fujinon 35mm f/1.4 lens mounted on it, while the Sony A7 II had the 24-70mm f/4 lens mounted on it. Granted the two might not be equivalent in light transmission, for now we are simply looking at equivalent brightness between these two cameras. At the same exposure settings of ISO 200, f/8 and 2 seconds, it is pretty clear here that the Fuji X-T1 on the left looks significantly darker than the image from the Sony A7 II on the right. This difference in brightness makes it difficult to compare the two cameras properly, as one simply shows no shadow detail.
Let’s take a look at what happens if we compare the two cameras at the same ISO and exposure settings, but after making exposure adjustments in post to see how much variance there is between the two. Here is the same image from Fuji X-T1, but this time adjusted by +0.85 EV in Lightroom:
Now the two look pretty comparable. I tried increasing the exposure on the Fuji X-T1 to higher values, but it resulted in over-exposure. Looking at the JPEG histogram in FastRawViewer and a comparable RAW histogram with exposure adjustments indicated that the above change was more or less accurate in most regions of the image. According to my estimates, the real difference in exposure between these two cameras is roughly 2/3 of a stop – the rest of the difference comes from lens light transmission levels. A similar conclusion can be made from looking at the DPReview Studio Test Scene. I downloaded RAW files from both cameras and compared them in Lightroom with 0.66 EV adjustment on Fuji X-T1. Here are two images compared at ISO 3200:
This result is interesting, because it shows that despite the 0.66 EV boost that I gave to the Fuji X-T1, its images at ISO 3200 actually still look a little cleaner than on the Sony A7 II (and that’s with Sony A7 II images down-sampled to 16 MP). If you look at the files, you can clearly see that the Sony A7 II contains more chroma noise than the X-T1. This essentially shows that even if we were to equalize the X-T1 sensor performance, it still can be a challenge for the A7 II in IQ at high ISOs – this confirms my findings from my Sony A7 II review, which as I have demonstrated, cannot match the Nikon D750’s sensor performance either, although the D750 also sports a 24 MP sensor. But we are not here to discuss the A7 II – we are here to see if Fuji has been cheating with their cameras when it comes to real ISO performance.
Fuji X-T1 vs Nikon D7100
Let’s take a look at another example and compare the Fuji X-T1 with another APS-C camera, the Nikon D7100. Here are images from both at ISO 3200, the X-T1 is again adjusted by +0.85 EV in Lightroom:
Although the X-T1 lacks the details of the D7100 (down-sampling from 24 MP to 16 MP did its job here), the image looks slightly cleaner in comparison. Again, this is because the X-T1 image is showing less chroma noise than the D7100. This is an interesting result, because we essentially have somewhat of an equivalent comparison here, considering that the X-T1 image saw a +0.85 boost in post.
Fuji Real ISO Comparison
Now that we know that Fuji is cheating by underexposing its images somewhere around 2/3 of a stop, let’s take a look at how the actual ISO of the Fuji cameras look like compared to the “simulated” ISOs. Here is a comparison of real ISO 3200 vs Fuji’s underexposed ISO 3200:
As expected, the real ISO 3200 does look noticeably worse than the simulated ISO – the 2/3 of a stop difference that I adjusted in Lightroom shows more noise. Here is ISO 6400 comparison:
Again, it is clear that the results are different – ISO 6400 with 0.66 EV dialed in Lightroom looks comparably worse, showing more chroma noise and introducing some artifacts to the image, particularly in the shadow area.
Conclusion
By now, it is a pretty known fact among the photography community that Fuji underexposes its images by around 2/3 of a stop to a full stop when compared to other cameras when shooting RAW and using most commercial RAW converters. There are all kinds of theories out there, with some people claiming that Fuji does this on purpose to look better, while others attribute this difference to Fuji’s X-Trans sensor and the demosaicing process. I have to say, that despite my attempts to normalize the RAW files by making adjustments, Fuji still looked pretty darn good compared to other cameras. The main source of this is reduced chroma noise, which is evident when you look at RAW files from both the above comparisons and other sources, such as DPReview’s studio comparison tool. That’s the main reason why Fuji looks so clean for an APS-C sensor. I do not know exactly how Fuji achieves this, but the X-Trans sensor and its demosaicing process are probably the reason for the reduced chroma noise we see in images.
Update: Thanks to some awesome people like Iliah Borg, we now know the reason why Fuji RAW files appear darker. Turns out that Fuji has a special tag (0x9650) in its RAW files that highlights the necessary midpoint compensation for RAW files to interpret and make necessary changes. Below are the values for the Fuji X-T1:
ISO 200 / 0.72EV
ISO 400 / 0.72EV
ISO 800 / 0.72EV
ISO 1600 / 0.72EV
ISO 3200 / 1.38EV
ISO 6400 / 2.38EV
So keep the above in mind when looking at Fuji RAW files and comparing them to other cameras. If you are using a RAW converter from Adobe (and potentially other RAW converters), make sure to look at the above table for adjustments needed to make images appear as they should. Big thanks to Iliah Borg and the LibRaw team for discovering the Fuji tags and letting us know!
Why not use a Standard like the Sunny 16 Rule to compare sensitivity? I love Fuji’s and was very surprised that for my X-T2 it was more like the Sunny 8 Rule!
Interesting discussion. I’ve recently retired from pro photography and have kept a set of old Nikon primes for use with a Fuji XE-2. I’m old-fashioned and I like to be able to use a hand-held meter to work out what I want to set my camera to. I can do it using the camera as well (assuming non-flash_.
I’ve found that in low light (ISO400 1/60th F2.8) the fuji needs about 2.3rds of a stop extra light than the meter settings would imply.
In Bright Lights, Sunny 16 area, It’s about 1.5 stops extra.
So, here’s my question. Is my camera/lens combinations causing this difference, or is this linked to the ISO difference discussed above. I’m not sure as I’m shooting jpgs,
If it was a consistent 2/3rds of a stop, life would be easy. Make the assumption that I know what I’m doing and that the camera is really shooting dark compared to a properly calibrated meter (two of them). Opinions welcome.
This article and the comments are confirmation that Digital Photography is full of whackos. Did people talk about this during the film days? I don’t know. I tended to avoid other photographers back then except when I was in the lab dropping stuff off (and even then most lab jockeys were not photographers but rather printers and retouchers).
All of you need to take a look in the mirror and ask yourself….is your hobby photography, or arguing about consumer goods? I mean really now….”cheating?” What is this, a card game? The Olympics?
In the film days we would test the film/camera and processing to come up with our own personals systems ISO.
thats true, I has tested on my nikon d800 and canon 6D using same lenses nikon 50mm 1.2, nikon is more brightness on same ISO setting…
Hi Nixda. I’m sure there might be something in what you say but at the end of the day, I need to crank my Fuji’s ISO up one stop more to get the same result as on my Canon FF and Crop cameras. Most folk buy a camera and read of great noise performance at a particular ISO and expect that to be comparable. People are therefore not really being given very helpful information by Fuji’s marketing department which I am sure is a deliberate strategy on Fuji’s part. It’s hardly surprising they then see Fuji as “cheating”.
I notice you don’t give any results of your suggested comparison in the 5th paragraph. Are you suggesting that a Fuj XT1i exposed at say 1/125s @ f5.6 with a 52mm lens ISO 3200 adjusted in Lightroom to the same brightness as a Canon 5D3 at 1/125s @ f4 with an 85mm lens also at ISO 3200 with brightness left as it is out of camera gives as good noise performance?
Hi William,
IMO, it is misguided to expect that identical numerical ISO values should give comparable results. I do agree, though, that the notion of a “standard” almost implies the existence of such equivalences. However, that “standard” is very fuzzy and has a lot of variables. Unfortunately, neither camera manufacturers nor reviewers have done a good job in properly educating the consumer.
Regarding the specific comparison I suggested, it was not meant to imply that one would get similar results, but to give a recipe for comparing cameras that might be more useful than comparisons based on numerically identical ISO values.
Sorry, also late to this discussion, at least on this site…
There is one aspect in all of these ISO discussions that has baffled me: what is the reason that one should expect that identical numerical ISO values between cameras should yield similar results? Given the fuzzy nature of the ISO concept as it applies to digital cameras, I wonder how realistic that expectation is. Large differences between expectations and reality then often lead to strong reactions, such as the “cheating” accusation, while people with a better understanding and well-adjusted expectations have more measured responses and usually merely note that there are differences in the ISO behavior and sometimes even explain how they can legitimately arise.
We often see comparisons between, say the X-T1 and the Nikon D7000, because they are both based on the same sensor. Then people scream when ISO200 on both cameras doesn’t give similar results in terms of exposure, image brightness and/or image quality.
But ISO200 on the X-T1 is base ISO with minimal amplification. ISO200 on the D7000 is one stop up from base ISO on that camera. The Nikon operates with reduced well capacity and half of its dynamic range at that ISO setting. That isn’t a useful comparison to begin with. Also, because the D7000 has two-fold amplification set, the exposure will of course be lower than the exposure chosen by the X-T1 at the same numerical ISO. Thus the notion that the Fuji “needs” more light to give similar image brightness.
Rather than comparing numerical ISO values, I would suggest comparing ISOs at the same stops above base ISO. So, compare D7000 ISO200 with X-T1 ISO400 (1 stop above base ISO), etc. You will find that the results are now much more similar between the two cameras.
Another useful comparison would be to set both cameras to the same focal length, angle of view, f-ratio, exposure time, and output image size, take shots, adjust them to match image brightness (using either in camera analog/digital amplification or external digital amplification), then assess image quality. This test is grounded in basic photographic (artistic) parameters and should appeal to practicing photographers who don’t want to think about the nitty-gritty details of sensor behavior.
Some speculation as to why Fuji uses digital amplification, even at base ISO:
Amplification is now a mixture of analog and digital amplification. Since analog amplification is lower, chances that the sensor output is clipped are reduced. The subsequent digital amplification of 0.72 stops can be reversed in a raw processor, if the raw processor honors that tag in the first place, thus “magically” recovering up to 0.72 stops of highlights. So, it’s basically a way to help the user preserve highlights.
Also, if Fuji’s ISO scale, based on sensor output, was calibrated to 100 at base ISO, like in other cameras, the subsequent digital amplification of 0.72 stops would shift the scale by ~1 stop to ISO 200 (165 or something, rounded up), which would look remarkably similar to the scale we currently have.
Sorry if I’m not clear. I know the meter will adjust but it still means going up at least one stop higher in ISO and the results don’t look so good as in a Canon or Nikon DSLR in terms of noise
I take it from this article that Nasim is arguing that the Fuji exposed manually at say for example, ISO 800 and f8 at 1/125s would give around a stop darker image in RAW than a Nikon at the same settings but that it doesn’t matter because you can boost the Fuji in LR to give as well exposed an image as the Nikon. Have I understood his position correctly?
Sorry to be late to the party. I’m very interested in this. Please can you clarify for me.
Are you saying that the Fuji exposed at say for example, ISO 800 and f8 at 1/125s would give around a stop darker image in RAW than a Nikon at the same settings but that it doesn’t matter because you can boost the Fuji in LR to give as well exposed an image as the Nikon?
Yes but you dont have to boost since the photometer will give you the correct measure so as not to have an underexposed image. So you will have the same photo luminance from both cameras but with fuji you will have more time or higher iso or smaller f number
Hello,
Im no expert at all, but i am thinking of the following:
1. If fuji really needed to allow or let the developers to use the midpoint value indicated at the tag, we would see fuji’s jpgs with 0.72EV more brightness than in the ACR developer. So i understand that fuji wants the camera to work with this -0.72EV (either in raw or in jpg). So its correct that we see in e.g. ACR underexposed images in relation with other companies’ cameras.
2. I try to understand why fuji decided on this and im thinking of this: in situations where you do not need to increase the iso in camera, you constantly increase exposure time by 0.72 stops (moving outside of the sensors optimal range), so as to get the correct exposure. Its like exposing to the left and then decreasing the exposure in raw developer, all done by the camera. This way you minimize the noise per photons recorded, trading off the dynamic range (or the highlights) and increase the bit depth/tonality of the shadows. If these are correct, this means that this sensor has great dynamic range, enough to let fuji record an over exposed image and correct it after the capture, to gain some decrease in noise, and tonality in the dark areas. This makes me understand that (if you are for the perfect exposure) its better to expose to the right, since there is enough headroom of the left in the recorded image.
Another trade off of this approach fuji chose is that you have to increase iso speed over 200 more often, when you need shutter speed, which is a minus for me.
On the other hand, when shooting with iso over 200, most often the image has large dark areas, so the previous theory may have even more point.
But in any case all this seems strange to me: capturing an image 0.72 ev beyond sensors optimal exposure, and then underexpose by 0.72 is like saying that fuji doesn’t agree/accept the sensor architecture.
I tested Oly EM10 with 12-40mm and fuji XT10 with 23mm and 35mm f2, and i found that on fuji, with the same exposure settings i had about -0.65 stops difference. This difference is not mainly from lens transmission differences.
Actually x trans sensors works as if its 125 native iso (with “little” highlight headroom and “big” shadow headroom), although its 200 native iso.
What do you think? My logic has any trace of truth or its too complicated to explain to me?
Also, Iliah, how do fuji prevents the highlight clipping with this method ( i would say the exact opposite), since the metering of the cameras, take into consideration this raw exposure handling.
Thank you all for the very interesting comments and the very interesting article!
Hi guys…
I think, that fuji IS NOT cheating – fuji as maybe one from last get it’s job right
fuji says that their ISO 200 is really something about 115-120 ISO – but they dont use it as ISO 100 like others
others cameramakers cheat with its iso settings (maybe except phase one…) – and thats a fact
x-t1 is the my best camera as i ever owned… best iso, manual settings, final results…
of course – thats my opinion
and, i really dont publish my work… i make photos for me, not for others…
sorry for my english
mF