I'd like a pair of binoculars for hiking. I don't have a specific use other than for looking off of overlooks, at animals, etc. What are the important things to look for in a good set of binoculars? There appears to be a very wide range of price and features to choose from.
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I researched this and there are a few factors
Aperture - This is the diameter of the objective (or front) lens and affects the amount of light taken in. Aperture is very important for low light situations. If you plan on using your binoculars near dawn or dusk, or under canopy, then you want a larger aperture. This is the second number used to describe binoculars. So 4x30 binoculars would have a 30mm aperture. Aperture unfortunately tends to linearly correlate with weight.
Magnification - Simple zoom. The first number and indicates the zoom factor. So 4 in our 4x30 example magnifies by 4 times. 9 should be more than sufficient for most hiking. Mountain hikes with long open lookouts may call for more.
Lens Coating - Lens coatings will significantly reduce glare and improve quality. At a minimum you want "Full coated" which means that all lens-air surfaces are coated. Multi-Coating will generally improve glare reduction and is exactly as it sounds... multiple different coatings.
Roof vs. Porro Prism - Roof prism will be smaller, lighter, and more durable, but will provide a smaller field of vision as compared to porro prism. For hiking you want the durability and lightness gained with roof prism.
Water/Fog Proofing - These features are critical if you expect to be in wet or damp environments. I have purchased (and wasted money on) more than one pair of cheap binoculars that did not have this. Waterproofing is usually accomplished with O-Rings, but fog proofing requires that the internal air spaces be filled with inert gas.
Optically, even cheap binoculars are very good these days so unless you need something special I wouldn't use this as a differentiator when looking.
Instead the three I see as most important are size, weight and robustness.
If they are going with you everywhere you need to make sure they will fit in your pack, not be too heavy and be able to take the odd drop, being bashed off trees, getting wet etc.
Let me share my rather limited experience.
I bought a 50BGN == $33 12-50x50* binoculars. Results:
There are several small loose parts of plastic inside the binoculars. They obscure small parts of the lenses. Not a very big problem, and I accept it for the money.
The 50 will collect more light through the large input lenses and provide crisper viewing, working well near dawn/dusk. However, the thing weights more than half a kilo - prohibitively heavy for any kind of backpacking.
The variable zoom is useless. Zooming in work, but the resolution is limited by the lenses and therefore no additional details appear.
If now I decided to buy another one for backpacking, I would go for the same price range, but smaller - for example 12x35.
* The first number (in this case a range from 12 to 50), represents the zoom factor. The second number, in this case 50, represents the diameter of the input lenses in mm