Before concluding this review, let’s spend a few lines explaining the ISO sensitivity graph, on which a selected ISO 1600 corresponds to a simple ISO 1000. This measured ISO remains constant for selected ISOs 3200 and 6400.
On the surface this is odd, but perfectly explainable:
A manufacturer has two options for increasing ISO sensitivity; either to order the sensor to increase its analog sensitivity, or after a picture is taken to tell the camera to amplify the image signal via algorithms at the RAW conversion stage.
Fujifilm decided to implement the second choice with the X100 and this processing action is normally invisible to the user.
As long as the algorithms used for the treatment are performing well, there is no real problem for the end user. As far as RAW measurements are concerned, the sensor’s maximum sensitivity is ISO 1000. That’s why none of our metrics goes further.