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I’ve just bought a mirrorless Fuji X-T20. In my first tests, it seem to ask for quite high ISO even in daytime indoor. So, as a test, I compared it with my previous camera, digital reflex Canon 400D.

With the same configuration, old Canon seems about +1 brighter than Fuji. How is it possibile?

Below the pics: first Canon, then Fuji. This two pics are shot with:

  • f/4.0
  • 1/15 sec
  • ISO 1660
  • Exposure Bias 0

About the cameras:

  • Canon lens is ES 28mm f/2.8
  • Canon raw size is 3888x2592
  • Fuji lens is XF 18-55mm f/2.8-4 and the shot is made at 25.4mm
  • Fuji raw size is 6000x4000

Canon Shot with Canon 400D

Fuji Shot with Fuji X-T20

Thanks.

  • What source(s) of lighting contributed to the scene? Sunlight through a window? Are there any clouds in your sky? – Michael C Dec 29 '17 at 22:55
  • Sunlight through a window with mosquito net, 3mt at the left of the camera, about 11 am – Radioleao Dec 29 '17 at 23:02
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    it is absolutely possible that two cameras have different scene representation at the same light conditions and exposure settings. It means their sensors are different, ISOs are nominal – aaaaaa Dec 30 '17 at 0:38
  • What is the Dynamic-Range setting of the X-T20? If it is 200% or 400%, it leaves room to not blow highlights which causes most of the scene to appear darker. – Itai Dec 30 '17 at 4:52
  • DR is 100%. I don’t know if 400D has this kind of setting – Radioleao Dec 30 '17 at 12:47
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In addition to all the other great answers I'd like to add that the Fuji x-trans sensor used in your cameras has been known to not really meet the ISO standard. Here is an excerpt from DPReview's review of the Fuji X-T1 (which also uses an x-trans sensor):

By our tests, the X-T1's measured sensitivities are around 1/2 - 2/3EV lower than marked, which is unusual for a modern camera. This means that for any given light level, the X-T1 has to use a significantly slower shutter speed, brighter aperture or higher ISO to get an image of the same brightness as an accurately-rated camera.

It's unusual to see this sort of discrepancy and we're disappointed that Fujifilm persists with a system that, while technically compliant with the ISO standard, ends up appearing rather disingenuous.

DPReview Review of Fuji X-T1' ISO Accuracy

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Your Canon has not exactly the same configuration. I suspect it to have the auto lightning optimizer on. You have the possible magnitudes: off/low/standard/high. And by default it is on standard.

Try to set it to off and you should have the same results. Try also to set the white balance to manual and to the same tuning, so you can have closest colors. You might have still some differences due to how each manufacturer is processing colors, and how the lens is processing the color.

[1] http://cpn.canon-europe.com/content/education/infobank/digital_camera_features/auto_lighting_optimizer.do

[2] https://digital-photography-school.com/what-is-canons-auto-lighting-optimizer/

1

There are at least two likely sources that are contributing to the variation you see.

  • The light coming in your window could be variable if the atmospheric conditions at your location are changing between the two shots. Clouds moving across the sky, for instance, can significantly influence both the brightness and the color of sunlight coming through a window.
  • The different ways each camera is capturing and processing the light to which it is exposed. Each sensor has its own sensitivity curves. Actual vs, rated ISO settings can vary significantly from one model to the next. To a usually much lesser extent, so can actual vs. target aperture values and shutter times. The way each camera calculates automatic white balance, automatic contrast adjustment, saturation, etc. will all affect the final outcome. Depending on the contents of a scene and the nature of the light illuminating it, just changing the color temperature/WB of the same raw file can affect the resulting brightness of an image.

In the case of your Canon 400D, the differences between using the "Standard" (slightly oversaturated and slightly too contrasty) Picture style with 'Auto Lighting Optimizer' turned on compared to using the "Neutral" Picture Style with 'ALO' turned off will almost certainly result in greater differences than seen those in your example images comparing your result with the 400D vs. the Fuji X-T20. One could post process the raw data collected by either camera and get a final result very, very close to the what you got with the other camera above.

Another possible source of the difference is that even though both lenses are set at f/4, one may have a higher transmissivity than the other. The f-number is an expression of the ratio between the diameter of the entrance pupil and the focal length. This is very useful for calculating/predicting the effect of a specific aperture setting on depth of field. The f-ratio does not take into account how much of the light passing through the lens is lost due to reflection and/or absorbtion. What we call 'T-stop' is a measure of how much light is actually allowed to pass through the lens. This is more useful for calculating exposure, but sometimes doesn't tell us as much as we want to know regarding depth of field. Most conventional lenses have a relatively small difference between the f-number and T-stop at any particular aperture setting, but there are some notable edge cases where the f-number and T-stop can be several stops different.

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I'm not sure if this is actually the problem, but this is probably one thing that is affecting the brightness.

Try looking at the T-stops of the lenses. (T-stop is like f-stop, but, tells how much light is transmitted through the glass, f-stop only takes into account aperture size). Your zoom lens may let less light through at the same aperture as your prime solely due to the number of glass elements in the lens (the more glass, the more light is lost).

That is assuming that the ISO for each camera means the same thing. If the fuji sensor is less sensitive, all ISO means is how much gain you are applying to the sensor data so if you get less sensor data (like from a different or smaller sensor) it will be darker even at the same multiplication level.

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Canon uses the Bayer matrix, which is 2x2 photosites per pixel, while Fujifilm X-T2, X-T20, X-E3 etc. use the X-Trans matrix, which is 3x3 photosites. The smaller the photosite, the less light the sensor gets, so pictures tend to be darker. That's why when I had to choose, I bought a X-T1 (16mpx) rather than the X-T2 (24mpx), for the larger photosites (and enough resolution for my needs, either).

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