Night Vision Alternative to FOM for night vision?

[nutation]

The figure of merit for an image intensifier tube contains information about signal-to-noise ratio and resolution,

FOM = SNR * lpmm

but leaves out equivalent background illumination. EBI is a sort of measure of image contrast, so it seems like leaving this out of the FOM calculation excludes some very important information about the tube. Since okayish EBIs tend to be around 1.0 (depending on the tube technology), would it make sense to measure overall tube performance by dividing FOM by EBI

tube score = FOM / EBI

So, the tube score would be increased relative to the FOM when the EBI is less than 1.0 (better EBI), and would be penalized for EBIs greater than 1.0 (worse EBI). Or would this score pack too many measurements into a single number to be useful?

 

[TheHorta]

Meh, since EBI is spelled out on every MFG spec sheet anyway, and MOST high-FOM tubes generally come with correspondingly low EBI figures, AND considering the fact that SN*RES is much more important than EBI, I don’t think incorporating EBI into a revised FOM will help anything. In fact, I think it would possibly be counterproductive.

EBI, outside of a very narrow set of environmental conditions, just isn’t that important. Give me a 3000 FOM tube with an EBI of 2.0 over the same tube in 2400 FOM with 0.5 EBI... All. Day. Long.

 

[RyanScott]

Above 64 line pair in an unmagnified system I can’t tell the difference. But a low EBI sure helps.

 

[TheHorta]

Above 64 line pair in an unmagnified system I can’t tell the difference. But a low EBI sure helps.

I’d basically agree with that, but there’s no way to factor EBI into a simple FOM equation that doesn’t give disproportionate weight to EBI. There just isn’t a stark difference in two identical FOM tubes, one with a 0.5 EBI and the other with a 1.5 EBI. 98% of experienced users wouldn’t be able to distinguish between the two 98% of the time.

The simple equation put forth by OP would radically skew the FOM result. The only way to incorporate EBI into a new FOM would be to turn a super-simple formula into a difficult math test — IMO.

 

[LivOutLoud]

Problem is allot of the specs play into each other. Gain is important and photocathode sensitivity as well.