The primary difference between the generations is the photocathode. For example Generation 2 uses a multi alkali photocathode while Generation 3 uses gallium Arsenide. Gallium Arsenide provides a significant increase in photoresponse and tube life. Other differences in performance will be image tube resolution, tube gain and signal to noise ratio. Therefore Generation 3 offers greater clarity but is generally more expensive than Generation 2.
\r\nGeneration 4 image tubes use a filmless technology which greatly improves the signal to noise ratio, lower halo. Generation 4 technology optics are often refered to as "Filmless & Gated" image intensifiers.