Finally, the device must be recognised as a system. Optics, image intensifier and power supply combine to provide a given level of performance. This performance level might change if, for instance, a new objective lens were substituted. The darker the conditions, the harder it is for the system to render a clear image. In increasingly darker conditions, a high quality IR-illuminator can offer a dramatic improvement in Night Vision performance.
Effective range is a balanced function of the system's gain, resolution and image magnification.
While a powerful objective lens will provide more magnification, it will also reduce the amount of available light captured. The lens can provide greater range only if it is of high optical quality and is used with a high-gain image intensifier with excellent resolution. If you plan to carry your scope in your pocket or briefcase, a small system is most suitable. A lightweight device will be more comfortable during extended viewing. Since you will be using the device in the dark, the switches and controls should be positioned logically and be easy to use.