If you do a search for "night vision equipment", you'll find SCADS of web sites that clarify the differences between the 4 (actually, now 5!) generations of night vision devices.
The #5 generation of night vision are NOT presently available for sale to the public. When/If it ever does, it will be SUPER-expensive. It is a "color negotiation" screen, instead of the usual green or gray screen on the current #1-thru-#4 generations.
The #4 generation is STILL subject to "registration" procedures for civilian sales. Prices will remain high, until the generation 5 models are made available.
The #3 generation, generally, will give you 60,000+ lumens of resolution when used with an infra-red illumination device. The clarity of the gen 3 equipment isn't obvious, other than at longer distances.
The #2 generation will also, generally, give you 60,000 lumens of resolution....depending upon the ACTUAL classification (some gen 2 are actually gen 1+ equipment, but with "enhanced" optics) (Add to that, some "gen 2" devices have only been rated at 30,000+ lumens, not the TRUE 60,000 lumens).
The #1 generation devices, generally, will give you somewhere between 15,000-30,000 lumens of resolution, depending upon the intensifier used in the device. When used with an infra-red unit, this will give you "decent" night viewing at shorter distances....and for less money.
They're still working on the DIGITAL aspect of night vision....plus the "zoom" aspect of optics.
If you're on a budget, like most of us are, look into the "Weaver" brand of monocular. It is a gen 1+ device, but also uses some sort of "gray" intensifier, instead of the usual green. They have also incorporated a "zoom" operation into the optics, which DEFINITELY impressed me! The small screen displays a black/white "picture", with an almost FULL screen of clarity (instead of the intensity being mostly focused upon the center). The "zoom" will increase the magnification from the "standard" 1.5x to 4x power. It would have been EXCELLENT if the optical lenses had been set at a true 1x, instead of the slightly magnified 1.5x!
Another great thing about the "Weaver" device is the relatively low price....around $200! Add to that, it uses "standard" "AA" batteries, instead of the more expensive lithium, and comes with a built-in array of WHITE infra-red LED's that are only "obtrusive" within short distances! (By the way, NO, I am NOT affiliated with "Weaver" or any other manufacturer!)
Prices? The "down-and-dirty" LOWEST price will only set you back about $100....but you shouldn't expect much from a cheapie. You'll get a "no frills" gen #1 device, with a low-intensity infra-red intensifier....good for about 25 yards.
TRIPLE that price (or more) for gen #1 goggles. The cheapest gen 2 will set you back about $500. The cheapest gen 3 will increase up to about $1,200. Gen 4? WHOA! $5,000+!
I could go on and on about such things as "active" and "passive" intensification units, "thermal" imaging devices, etc. I currently own gen #1, #2 and #3 devices, along with gen #1+ devices. I've used gen #4, and was lucky enough to get a glimpse through a gen #5 unit for a few minutes, but they are WAY out of my budget! I used one of the first "passive" gen #1 units (starlight) when I was in South Vietnam, back in 1967-1968, so I KNOW how the technology has advanced since then.
