View source for Figure of Merit (FOM)

Figure of Merit (FOM) is a dimensionless value that has been introduced as an arbitrary reference and shorthand overall performance grade of an [[Image Intensifier|image intensifier]]. 

It is calculated by the formula <math display="block">\mathrm{FOM} = \mathrm{Res.} \cdot \mathrm{SNR}</math> where <math display="inline">\mathrm{Res.}</math> is the [[resolution]] (in lp/mm) and <math>\mathrm{SNR}</math> is the [[Signal-to-Noise Ratio (SNR)|signal-to-noise-ratio]]. 

== Considerations ==
Due to the resolution being usually around 2-3x higher than the SNR it has a larger impact on the value, although some consider SNR the more important factor of the two.

The FOM is not to be taken as a tell-all-end-all as a full spec sheet gives far more detailed insight as to a tubes performance albeit it might seem slightly more esoteric to people who are unfamiliar with interpreting a spec-sheet.

In order to fairly judge a tubes FOM rating one should have some knowledge of the category to which a tube belongs as well as an average or minimum number for at least one of the factors involved in producing a FOM rating. If one knows that a particular category of tubes has a minimum SNR of 30 with average at 36 then going by FOM alone when considering an individual tube of that category is less arbitrary.

=== Downsides ===

* The same FOM can be produced by a low SNR and high resolution and vice versa
* Other important specifications like [[gain]], [[sensitivity]], [[halo]], [[Modulation Transfer Function (MTF)|MTF]], ... are not taken into account

[[Category:Technology]]