What's up with Fuji ISO values?

[DVasquez]

Have you tried comparing the images (shot at the same manual settings) after making whatever post processing adjustments required? Compared them with the Fuji ISO boosted one stop?

I don't know which one will look better, but that is the question.

I did a quick test when out on a shoot.
It isn't done under lab conditions, but it's real enough for me.

Here is an example - note that there was a difference in camera settings:

• D500 was set to ISO2000 - 1/2500s - f6.3
• X-T3 was set to ISO2000 - 1/2000s - f5.6

I removed all NR and sharpening in Capture One Pro - including output sharpening.
This isn't a test for sharpness, but noise is relevant.

D500



X-T3



The X-T3 still needs another 1/4 stop of exposure to match the D500 despite already having about 2/3 stop advantage in the shutter speed and aperture.

This is applicable for the centre of the frame.
The XF100-400 vignettes heavily at f5.6 @ 400mm so away from the centre it probably needs another 1/2 stop exposure to match the D500 image (shot with Nikon 200-500/f5.6).

In terms of noise I don't see much of a difference between the two.

Here is the X-T3 image with +0.2 exposure and full anti-vignette (Light Fall-off) applied in C1P:



I will let you judge for yourself if there is a noticeable difference in image quality.
There is certainly a difference in shutter speed and aperture.

madsbjerke.com

You are comparing apples to oranges. Those are 2 different lenses which will have different T values. F-stop is not exactly how much light a lenses lets in as lens element count and coatings can effect it. Typically lenses with fewer element counts are actually brighter, all things being equal.

 

[Tony Beach]

Fuji underexposes to protect highlights. Nothing to worry about.

If the camera takes that stop away in effective exposure it makes the rest of the system very expensive.

In essence what you experienced was both cameras captured the scene equally and I believe if you used a program such as "Raw Digger" it would show very similar values for the raw files. The D500 simply boosted the brightness by nearly a stop with a tag on the raw file for the raw converter.

I have learnt a lot about iso standards from this thread so it's been useful for me.

I was initially very surprised to see the darker images out of the X-T3 and that prompted my curiosity.

ISO values are really just a guide as to how how much light we're exposing the sensor to at capture, nothing more.

More precisely, it defines the EV the manufacturer recommends to attain "well-exposed sRGB images. The industry standard is to average the scene to 18% gray, give or take a third of a stop (which adds up). See "The Recommended Exposure Index (REI) technique" here:

https://en.wikipedia.org/wiki/Film_speed#Digital_camera_ISO_speed_and_exposure_index

The resulting ISO is arbitrary (as stated in the above link), and the differences between the D500 and X-T3 come down to what each consider "well-exposed" with the camera's default image settings ("Picture Controls" on the D500). Given that, you can either change the exposure or the image settings, and doing the latter is what changes the ISO.

In your example the D500 ISO setting tagged the file to be nearly a stop brighter when converted by Lr but that's no different than you adding that brightness in Lr to the X-T3 file because in reality they both received the same exposure at capture and the sensors are very similar in performance.

Adobe Camera Raw (ACR) works under the hood to apply brightness to different files. Inasmuch as those correspond to what the manufacturers do with those files is at Adobe's discretion.

If this bothers you then I suggest setting the exposure comp dial to +2/3rd's for normal shooting and your results will be similar to the D500 but you'll also loose 2/3rd's of stop of highlight headroom in the raw file just as does the D500.

You will also either lose DOF and/or shutter speed. To actually make them more or less equal in that regard just boost the brightness setting on the X-T3.

 

[rwbaron]

Fuji underexposes to protect highlights. Nothing to worry about.

If the camera takes that stop away in effective exposure it makes the rest of the system very expensive.

In essence what you experienced was both cameras captured the scene equally and I believe if you used a program such as "Raw Digger" it would show very similar values for the raw files. The D500 simply boosted the brightness by nearly a stop with a tag on the raw file for the raw converter.

I have learnt a lot about iso standards from this thread so it's been useful for me.

I was initially very surprised to see the darker images out of the X-T3 and that prompted my curiosity.

ISO values are really just a guide as to how how much light we're exposing the sensor to at capture, nothing more.

More precisely, it defines the EV the manufacturer recommends to attain "well-exposed sRGB images. The industry standard is to average the scene to 18% gray, give or take a third of a stop (which adds up). See "The Recommended Exposure Index (REI) technique" here:

https://en.wikipedia.org/wiki/Film_speed#Digital_camera_ISO_speed_and_exposure_index

The resulting ISO is arbitrary (as stated in the above link), and the differences between the D500 and X-T3 come down to what each consider "well-exposed" with the camera's default image settings ("Picture Controls" on the D500). Given that, you can either change the exposure or the image settings, and doing the latter is what changes the ISO.

In your example the D500 ISO setting tagged the file to be nearly a stop brighter when converted by Lr but that's no different than you adding that brightness in Lr to the X-T3 file because in reality they both received the same exposure at capture and the sensors are very similar in performance.

Adobe Camera Raw (ACR) works under the hood to apply brightness to different files. Inasmuch as those correspond to what the manufacturers do with those files is at Adobe's discretion.

If this bothers you then I suggest setting the exposure comp dial to +2/3rd's for normal shooting and your results will be similar to the D500 but you'll also loose 2/3rd's of stop of highlight headroom in the raw file just as does the D500.

You will also either lose DOF and/or shutter speed. To actually make them more or less equal in that regard just boost the brightness setting on the X-T3.

Good points.

In essence though I think the OP was concerned that at the same shutter speed and aperture the X-T3 was underexposing by nearly a full stop compared to the D500. In this case raw files and ooc Jpeg's need to be considered differently. This may be true for ooc Jpeg's but as far as raw files the exposure at time of capture should be very similar if not identical between the two sensors. Based on shutter speed and aperture both sensors received the same amount of light at capture. The difference is the D500's ISO calibration tagged the raw file with a higher brightness value which led the OP to believe the D500 was more sensitive to light.

In the end the X-T3's ISO calibration is biased to provide more highlight recovery whereas the D500's is more for shadow protection (D500's is more biased to ETTR).

I have to think on this further but it may be that the case could be made that it's Nikon that's "cheating" on their ISO values. ;-)

Bob

 

[Truman Prevatt]

Fuji underexposes to protect highlights. Nothing to worry about.

If the camera takes that stop away in effective exposure it makes the rest of the system very expensive.

In essence what you experienced was both cameras captured the scene equally and I believe if you used a program such as "Raw Digger" it would show very similar values for the raw files. The D500 simply boosted the brightness by nearly a stop with a tag on the raw file for the raw converter.

I have learnt a lot about iso standards from this thread so it's been useful for me.

I was initially very surprised to see the darker images out of the X-T3 and that prompted my curiosity.

ISO values are really just a guide as to how how much light we're exposing the sensor to at capture, nothing more.

More precisely, it defines the EV the manufacturer recommends to attain "well-exposed sRGB images. The industry standard is to average the scene to 18% gray, give or take a third of a stop (which adds up). See "The Recommended Exposure Index (REI) technique" here:

https://en.wikipedia.org/wiki/Film_speed#Digital_camera_ISO_speed_and_exposure_index

The resulting ISO is arbitrary (as stated in the above link), and the differences between the D500 and X-T3 come down to what each consider "well-exposed" with the camera's default image settings ("Picture Controls" on the D500). Given that, you can either change the exposure or the image settings, and doing the latter is what changes the ISO.

In your example the D500 ISO setting tagged the file to be nearly a stop brighter when converted by Lr but that's no different than you adding that brightness in Lr to the X-T3 file because in reality they both received the same exposure at capture and the sensors are very similar in performance.

Adobe Camera Raw (ACR) works under the hood to apply brightness to different files. Inasmuch as those correspond to what the manufacturers do with those files is at Adobe's discretion.

If this bothers you then I suggest setting the exposure comp dial to +2/3rd's for normal shooting and your results will be similar to the D500 but you'll also loose 2/3rd's of stop of highlight headroom in the raw file just as does the D500.

You will also either lose DOF and/or shutter speed. To actually make them more or less equal in that regard just boost the brightness setting on the X-T3.

Good points.

In essence though I think the OP was concerned that at the same shutter speed and aperture the X-T3 was underexposing by nearly a full stop compared to the D500. In this case raw files and ooc Jpeg's need to be considered differently. This may be true for ooc Jpeg's but as far as raw files the exposure at time of capture should be very similar if not identical between the two sensors. Based on shutter speed and aperture both sensors received the same amount of light at capture. The difference is the D500's ISO calibration tagged the raw file with a higher brightness value which led the OP to believe the D500 was more sensitive to light.

The sensor is not film. The sensor as a base sensitivity. However, CMOS sensors have an amplifier at each detector location between the detector and ADC. Film does not have this. What the raw file is - is not the values of the detector it is the values after the ADC. The amplification is a function of the camera design and the ISO setting.

So the raw file is not the actual values of the detector output but the amplified version that will result in the proper exposure on the JPEG.

A lot of these issues would disappear if Fuji (and other camera makers) would give us a raw histogram. Even the histogram shown is based on the JPEGS - not the raw data.

One should think of ISO with respect of JPEGs not raws. We know that the Fuji raw is underexposed by about 2/3 stop to protect highlights in the out of camera jpegs. It is repeatable. If you want fully exposed JPEGS, simply crank up the EC by 2/3's Of course your histograms would be useless since they only apply to the raws.

If Fuji would give us an option of JPEG histograms and raw histograms it would be a big step forward.

In the end the X-T3's ISO calibration is biased to provide more highlight recovery whereas the D500's is more for shadow protection (D500's is more biased to ETTR).

I have to think on this further but it may be that the case could be made that it's Nikon that's "cheating" on their ISO values. ;-)

Bob