Gen 1 - If it's not top of the line, don't buy it. As far as the scope of night vision goes, this is basically comparing a bicycle to a car. However, it's still better than walking!
Gen 2- Bottom of the line stuff is subjective. It has much better amplification than gen1, but the cheap enough tubes can be so noisy and low resolution that they could actually be harder to use than a top end gen1. Top end gen2 stuff (Photonis XD4, XR5, INTENS tubes) is on par with lower end gen 3 and even comes with some high end features like autogating. Expect to spend anywhere from $2200 (used) to $5000 (new) for gen2
Gen 3- Since everyone buying gen3 is pretty well buying old military stuff; ANVIS and PVS-14s, there's only 3 really important things to remember:
- OMNI specs are *minimum* specs, but OMNI VII has the highest minimum spec. That being said, it's possible to get an OMNI V that's just as good as an OMNI VII, but there's no spec sheet, so there's no telling unless you have them side by side for a direct comparison.
- How does one check that? Well don't take the seller's word for it, look through the ocular lens at an angle, you should see white writing
like this (you shouldn't have to remove the lens to see it), and then you correspond it with
this chart. If it doesn't have writing on the back, it may have writing on the SIDE, which requires you to open the body. Or it could be raised black lettering, so use a flashlight or take the ocular lens off to check.
- Military tubes don't have spec sheets. Commercial tubes do. If it doesn't have identifying marks on the tube, then it's commercial. Now that's not necessarily a bad thing, as long as you either have a spec sheet, or can compare it to something you know side by side. Don't pay for an OMNI VII then later find out it's just an old repacked Litton tube.