"Fair" in photography is when the same amount of light (roughly the same number of photons) is allowed to reach the sensors under a comparison.
When ISO is 6400 on both FF and MF, the latter is allowed to receive ca. 2.5 times more light. I actually made a mistake in my previous post: to be equivalent, the FF ISO should be near 2600 on a FF camera when the Phase One ISO is at 6400.
Yes, when a FF and a MF camera are set to the same ISO, aperture, and shutter speed, they will both expose to the same EV. Since aperture and shutter speed are the same, the "amount of light per sensor area" (in lux*sec or lumen*sec per sq meter) is the same, and the bigger MF sensor receives more total light.
By comparing FF ISO 2600 to MF ISO 6400 you would compensate for this area difference, and reveal the "per sensor area noise" performance of the sensors.
May 20, 2026 at 09:55 AM
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