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Cascading single stages by coupling lens systems is rather inefficient as the lens systems limit the obtainable gain quite severely.

Channel-type image intensifiers are capable of achieving high-gain values ; ;

they suffer, however, from an inherently low resolution.

Image intensifiers based upon the multipactor principle appear to hold promise as far as obtainable resolution is concerned.

However, the unavoidable low-duty cycle restricts the effective gain.

TSEM tubes have been constructed showing high gain and resolution.

However, electrostatic focus, important for many applications, has not been realized for these devices.

Resolution limitations with electrostatic focus might be anticipated due to chromatic aberrations.

Furthermore, the thin film dynodes appear to have a natural diameter limitation wherever a mesh support cannot be tolerated.