What is FOM or Figure of Merit?
This figure is used by NATO to measure the overall performance of a tube and also the USA to restrict exports. The FOM is simply calculated by multiplying the resolution (how detailed the image is) by the signal to noise ratio (how well the tube makes an image in low light). The various tubes that are around these days have the following average FOMs. USA Gen2+ 350 DEP Commercial 600-800 Russian Gen2+ 1000 Photonis-DEP Gen2+ 1200 USA Gen3 1200 / 1600 SG 1250 HG 1600 XG 1800 Photonis-DEP XR5 1800 Iincidentally 1600 is the NATO maximum. So in simple terms the higher the FOM is, the better the image will be.
