Where's the variable gain control?

Having some experience with night vision photography, I found that one of the most helpful features in getting the right shot is variable gain control. Variable gain control is typically a knob that allows the user to manually adjust image tube brightness by increasing or decreasing for greater image contrast in varying light conditions ( basically like a dim control ). This feature is available on the ITT NEPVS-14 and it basically sets the NEPVS-14 apart from other popular monoculars that do not offer this feature. Having used the NEPVS-14 with digital camera, I've found that it can really make a break a shot. This is a feature that should be embraced by anyone manufacturing night vision camera related equipment.