This is a quick guide, essential things to bear in mind before you buy a pair of binoculars

1. Normal optical binoculars are not designed to use at night, without light, they don't work, simple as that, a pair of night vision googles cost at least £250, they generate artificial light to make things seeable. So, don't be fooled, night vision, night activated, etc, etc, all that crap, they are lies. Good coated lenses help to absorb light to make things look brighter, but as I said without light, they don't work. Please use your primary school common sense.
2. Multi-coated is the king, these lenses look like green, purple ish; blue coated is ok, but not as good as green; red-coated lenses are crap and cheap, they reflect the light away rather than absorb light, therefore what you see through these binoculars are much darker.  
3. For exmaple, a 16x50 pair will gives you bigger image of an object than 7x50, BUT, it gives you a smaller image overall, i.e. a narrower view.
4. Zoomed image may not be as sharp and clear as normal image, for example a pair of  7-21x40 give you a bigger image of one thing but it may not as clear as 8x40 give you. Also, a much smaller angle of view.
5. Zoom binoculars only have the following models because only these designs are possible to produce, therefore any models you can't find in the following list is marked wrong delibrately to fool consumers.    7-21x40, 8-24x50, 9-27x60, if you know bit maths, you will know what will follow.
6. 7x50 is bigger and heavier than 8x42, 8x42 is heavier than 8x40. 
7. You get what you pay.  

I really hope everyone will can get the best value for binoculars and enjoy them for all their lives. And, that's what I and my staff are working for.