When considering purchasing any N.V. rifle scope, some thought should be given to the following.
What do you want to shoot? This may seem like an unnecessary question, but it obviously governs the calibre of the firearm to be used.
This in turn can influence your choice of scope.

Night vision scopes have been developed from military applications, where most were designed for use with the 5.6mm military round (.223), and as such no real recoil is produced.
Make sure your choice is one that will withstand higher recoil if you intend to use "heavy calibre" cartridges, or be prepared to use a recoil reduction system of some kind.
Apart from the resistance to shock on the internal electronics, eye relief is critical when you intend to use even say a .243W, but certainly .308W, .270W and upwards. Some N.V. scopes can have as little as 25mm eye relief !

With some of the upper level thermal scopes it is recommended that you use some form of recoil reduction system. This can be a muzzle brake, a "recoil reducer" or a special mounting rail that allows the scope to slide on the mount etc. (Always worth considering anyway due to the cost of these items). Some manufacturers do state the resistance to shock but not all. GSCI image intensifying N.V. scopes are able to withstand .50 cal and is stated as such.  

Pulsar Phantom, image intensifying N.V, the new thermal Pulsar scopes and Pulsar Digital scopes are good to .375 H&H.

Recoil reduction of some sort will also help with the limited eye relief found on some manufacturers products mentioned above.

As stated previously, it is essential that you can see what is in the background behind your target, meaning you must have the ability to see and identify any potential hazard that may exist far beyond your intended range, whatever that range may be.

With regard to "seeing", due to the fact it is more difficult shooting at night with any night vision, magnification should be considered.   Generally speaking, most shooting carried out in daylight, scope magnification of 6X or higher is used, it would therefore be logical to use as high a magnification as possible at night. High magnification is not very common in image intensifying NV, therefore 4 and 6X would be considered as being fairly high while still keeping the lens size under control. When you are looking at night vision of any type, you need to be aware that as the optical magnification rises the system sensitivity decreases unless a faster lens is also used.

For thermal imaging, magnification is "high" at 4X, and this is where 17 micron pixel 640 X 480 FPA comes in to its own, as the image is still sharp when digital zoom up to 2X is used and quite acceptable at 4X zoom. Lens size (f number) also applies, as above, with thermal too.

Read specification lists carefully as there is a thermal scope advertised as 25 micron & 4X - 16X magnification, but if you look carefully you will see it has a 50mm focal length, (2X optical) and the 4 - 16 refers to digital zoom only. ( 6 X optical magnification is now becoming a real proposition with the use of 17 micron with an appropriate sized FPA, lens speed does drop slightly but is proving to be very effective)  

High magnification has limitations with day scopes too.

How about a "clipon" device rather than a dedicated night vision scope? OK, but it is important to note that if the chosen device is to be used behind the day sight, the inbuilt sensitivity of the night vision unit is reduced by the losses in the day scope. Depending on the day sight used this can be a significant reduction. Therefore it is far preferable to select a device that operates in front of the day sight. This way the overall sensitivity of the device is preserved.   Another benefit gained by front mounting, is that your shooting position is still the same and does not change the way you hold the rifle to accommodate the extra length of the overall sighting system.

A WORD OF WARNING!   When choosing a N.V. scope, don't be misled by advertising "pictures" claiming the images shown indicate what can be attained with "their" equipment, especially where the target object almost fills the complete picture. This means that the target is VERY close and not at the distance a shooter would normally expect to operate. At the same time the picture may be computer enhanced or even "manufactured" to improve the image quality.  The result is very misleading, but unfortunately, does happen quite often.
An example of this can be seen with a prominent night vision / thermal manufacturer, won't mention a name here, but look around. It seems that this company's products are not highly regarded in the States either.

It is fully accepted that it is extremely difficult to reproduce an image that really represents the product in question. With respect to thermal imaging, due to the fact that when a picture or video from a device is printed or displayed on a computer for viewing, the image is naturally GREATLY enlarged from the actual screen size within the unit. The internal screen is about one tenth of the size of the average printed picture and the internal "picture" is somewhat less than one megapixel, while the image on the internal N.V. screen appears quite satisfactory to the viewer. Therefore an "enlarged" printed  picture from thermal NV, will never be like one that can be obtained from a digital camera, even from one that would, on today's terms, be considered very low definition. With image intensifying NV a large "target" image is obviously close and a lot of images are taken with large amounts of available light to give the best impression. These images are taken with a camera behind the NV device.

As a final word, when using a night vision rifle scope you are obviously shooting in the dark, always choose a suitable calibre for your intended target and only shoot at a conservative range. It is not like shooting in daylight or even when using a spotlight.  


    A "manufactured" image of a SUPERWIZZ NV scope.      Sharp, clear image, but not through night vision equipment !