The Fujifilm FinePix X100 has been delighting photo enthusiasts with its high ISO low noise capability, with low noise up to ISO 6400. However, according to tests performed by DxOMark, the FinePix X100’s highest ISO is ISO 1000, with image quality from ISO 1600, 3200 and 6400 all giving the same results as ISO 1000.
According to Focus Numérique, this “strange” behavior can be explained by how camera manufacturers apply one of the following two strategies to obtain high ISO images: up the sensitivity up to a certain ISO or apply firmware processing. The X100 apparently innovates by applying both strategies: up the sensor sensitivity to a maximum of ISO 1000, then process images for higher ISOs.
source Focus Numérique