Binoculars may seem like simple technology, but it's a little more complicated than putting a couple of magnifying glasses to your eyes. Without prisms in the binoculars, which are used to reflect light and turn a magnified image right side up, you're going to be attempting to spot yellow-shafted flickers upside down. As if birding could be even more frustrating.
If you're looking to purchase a pair of binoculars, one of the first decisions you'll have to make is whether you'd like a roof prism or Porro prism pair. What, no burning preference? Keep in mind that binoculars work by using a prism to lengthen the light path between the objective lens (that is, the front lens that captures the light) and the eyepiece. Lengthening the prism, therefore, can increase the magnification without increasing the length of the binoculars.
That works two ways. Porro prism binoculars have objective lens tubes that are offset from the eyepieces; the prisms angle from the eyepieces to the objective lenses. Roof prism binoculars have two straight tubes, making them smaller and more compact.
If you're still not sure if you should buy your "Team Porro" or "Team Roof" T-shirt, there are a few advantages and disadvantages to them. While many assume that Porro prism binoculars are going to be more expensive because they're bigger and more substantial, roof prism binoculars (the straight ones) can actually cost more to make due to the more complicated manufacturing process for the internal angled prism. But beware: Porro prism binoculars usually have a higher quality image and less light loss (which makes the picture clearer). Although roof prism pairs can absolutely have a comparable optic, their compact design and complex prisms make the higher-priced roof prisms a better bet for a quality binocular.
Now that you've had a chance to decide if you want the more compact roof prism binoculars or the less expensive quality of the Porro, let's move on to some of the more specific uses of binoculars and the best buys for them.