The X-Factor of Fudging ISO

There are two implications if the Fuji ISO is not accurate:

1) When using a light meter (studio work, flash exposure calculations) the images would be underexposed.

2) When comparing noise from one camera to another (that does not "inflate" numbers", keep reading the Nikon D800E is exactly the same), the Fuji would have an advantage.

I think both are valid considerations.

One user here already said he tested his camera against a Sekonic light meter and found his Fuji to be the same.

I have just compared the spot meter reading from a Sekonic L758-D of a Kentmere gray card against both my XE-1 with 35mm f1.4 and Nikon D800E with a 85mm f1.4. I tried a variety of ISO (800, 1600, 3200 and 6400) and aperture (f16,f8,f2.8) combinations and the Fuji XE-1 and Nikon D800E were EXACTLY the same in EVERY case. According to the Sekonic though, they were both between 1/3 and 1/2 of a stop less sensitive than the chosen ISO.

In other words, the Sekonic metered the card at ISO 800, f8, 1/30 and the Fuji ISO 800, f8, 1/25. I would see this as too close to call if it weren't the exact case for 12 readings. The Fuji NEVER matched the light meter and it was always 1/3 to 1/2 stop less sensitive.

I use "less sensitive" so it is easy to see that ISO 800 is really ISO 640.

I just chucked a D3100 and it is the same as the other two.

IT BEGS THE QUESTION, IS THE SEKONIC ACCURATE?!

I checked a brand new battery in it and got the same result.

I, for one, believe that it is CRITICAL that camera manufactures do not start sliding the scale. It would be like selling 15 oz. of gold and calling it a pound. ISO sensitivity is an exact standard. For a given amount of light ISO, Shutter Speed and Aperture should result in the same exposure.