First of all, for hunting I carry some Luepold 10 X 40's.
In the diferent bug out packs/car./truck, etc, I toss some cheap 8x20's. Since they are ten bucks I got plenty of them, no biggie if they crap out. the Lupy's (250.00) are for sure, though.
Now a primer on nomenclature:
10X40: the first number is how many times the scope or bino multiplies the image. so an 8 power is not as powerful as a 10 power, and a 12 power is getting close to too hard to hold still.
A 16 power is almost worthless, since you can't hold it still, and it won't focus close up.
The second number (8X30) is how many mm it is across the objective lens (the lens closest to the target). A 30 mm lens is not quite as bright as a 40, and a 50 mm lens is pretty big, and bright.
If you see a number like this: 3-10X50 it means that this is a ZOOM model, that is you can find the target at 3 power, zoom up to 10 power for detail, with a 50 mm Objective lens.
Zooms are inherently slightly to markedly less in quaility. Except the Zwarovski that goes directly from 8-12 power in one click. Those are well made.
Quality: a 39 dollar pair of binos (walmart bushnells 10 X 40) is noticably fuzzier than a 250 dolllar Luepold 10x40.
Go into the 1200 dollar range (Ziess, Leika, and Swarovski especially) and you get absolutely crystaline images, with very close focus, and rapid focus. If you can afford it.
For hunting, bird watching, and warrior use, a 10 power is probably best all around strength.
types: the porro prism is the classic shape, It's the bino with the hips.
the roof prism is more of a straight line shape, more compact, and clearer image. Easier to make a quality bino with that style.
compacts: These are almost always Roof Prism, with 8 to 10 power being most found. Up to about 25 or rarely 30 mm objectives, before you have to jump to larger frame. easy to loop the string (rarely a full neck strap) through a pocket button hole and drop the bino into a pocket. I have a Tasco 12X 25 that I really like.
Exit pupil: this is critical in ease of use: the larger the exit pupil the easier it is to find what you are looking for.
The exit pupil is the dot of light coming outof the lens closest to your eye. If you are too close or too far from it, it looks like a bubble swimming around in front of you. At just the right distance, the entire image opens up into a full field of view in your eyeball. A larger exit pupil is easier to get right fast.
Eye relief. This is what allows you to hold further away, and still get a good picture.
Roll down cups: these are for those who wear glasses. Roll down the cups, and put the binos directly against your glasses, and geta good view.
Diopter adjustment: this is what lets you set one eye diferently from the other, when your eyes don't really match, but you haven't admited you need glasses. OR it allows you to take off your glasses, and adjust to your vision, and get a perfect view.
Physically go to a place like Cabellas, or Sportsmans Wherehouse, and try out several. Look for the clearest picture in the price range you can afford. Then see how close you can focus. A really good one will focus about 6-8 feet from you. How long do you have to twist to focus from your feet, to way across the building? Try to read signs at diffent distances, especially small print or complicated print. That tells you how good the lenses are.
Is it easy to get into a good hold, with a clear single picture?
many inexpensive binos are now water proof, and purged with nitrogen.
Avoid Chinese binos, and you may even pass on Barska (russian?)
I hope this helps, good luck
By the way, they all come with a pouch that you can hook to your belt, I prefer them closer to hand, and use a harness for carrying, so I can keep it off my neck. Walmart, 14 bucks.
