The most important factors for picking the right product for you are as follows:
Clarity is directly connected with the resolution. The relation is quite simple – since the resolution is measured with lines per millimeter, the higher the lines the greater the quality will be. This is becoming somewhat less important as even consumer grade products have improved their level of clarity in the last few years.
When dealing with night vision scopes, it is important to know the necessary recognition range. Regardless of all the technological advances, night vision technology has still not reached the point where it can function as a rifle scope, i.e. having the ability to see over hundreds of yards. The total range is not nearly as important as the recognition range of a night vision scope. Most manufacturers release recognition ranges for different lighting conditions like full moon, quarter moon, starlight only, or overcast. Naturally the range decreases as the amount of light decreases, since night vision quality depends on the available light.
With night vision devices, the higher the magnification the bigger and heavier the optics. For freedom of movement and comfort, use a lighter optic while heavy optics are meant for static observations.
If you are about to spend several hundred or even thousand dollars on a piece of night vision equipment, it needs to be a long term investment. So before deciding on the make and model, consider the quality of the weatherproofing and the known longevity of the electronics and optics.
Infrared Illuminators (IR
When buying a night vision device, check if it has an infrared illuminator or the option to mount one. Infrared illuminators emit infrared light which is reflected back by the surroundings into the night vision set, making the image brighter. This addition is especially useful in situations where there is a near-total lack of light. Notably, IRs have a limited range, depending on their size.