Before 2019 echo have same technology and are 4G fail out.
I dont have reliable information about eventual different coating or different PSU.
Wich mean the echo tubes are build in a very different line what doesnt even makes them a 4G.
The 4G benefit of a specific coating with biggest spectral sensitivity.
Gain:
For example 14000 gain (photonis) x pi x 1.1 (metric difference in measurement with the 2856k light)
14000x3,14x1.1=48300 equivalent gen3
You can apply the same factor for Srn.
1.1 factor:
Here à part of David (CJ7Hawk) text on ar15.
Also, as a part of my research, I developed a factor ( co-efficient ) for comparing 4G tubes to Gen3 tubes directly, based on specifications which include the photocathode response in any way ( S/N, PC, Gain, etc ) since the 2856K light standard used in measuring tubes creates a different response to what is experienced in the field - as a result of atmospheric glow phenomena. It's normalized around 1.0 which represents a Pinnacle tube photocathode, as published by ITT ( Now Excelis ). - As a result of this, 4G metrics should be multiplied by a factor of 1.1 over datasheet - this means that a 4G S/N of around 32 would be equivalent to a Gen3 S/N of around 35 - This is it's Night Sky Co-efficient, and predicts the difference in field performance between the two technologies, since it's otherwise difficult to compare them. (End of quote)
Ebi:
To have the equivalence between Gen3 and Gen 2 photonis.
You can multiply the G2 value x10. And vice versa.
Photocatod sensitivity:
A 4G tube with 2200 fom was measured.
The result of photocathode response measurements on the 4G Wp was: Sensitivity >1000 ua/Im, at 830nm >130 ma/W.
This latter number is 80% more than the xr5 value. It's near to what their patent claims, it claimed a 80% increase at longer wavelengths, seems that is exactly what's happening with the 4G for reference, gen3 have still 60% more than 4G. With about 210 ma/W.
If you want to have the gen3 equivalent for the sensitivity.
In the night vision documentation (photonis, ITT...) , it's accepted that a generation 3 tube filmed with a sensitivity of 1800 is equivalent to 650 for a generation 2. Due to the ion barrier.
So you can apply a 2.77 factor.
For example the 1000 ua/lm will do 2770ua/lm in Gen3 filmed.
If you want to push your calcul you can extrapolate with thin-filmed you will save 10 to 12% of efficiency and idem for filmless.