The selection of quality binoculars available at reasonable prices has never been greater. When shopping for a new set, you may notice that all are either referred to as Porro prism or roof prism. But what is the difference, exactly, other than price point and physical difference?
First, the technological basics: Porro prism or roof prism refers to the type and configuration of the internal prisms used to magnify and transmit light through the binocular to the eye. Below explains the path of light and internal prisms for each one.
Now that you've been versed on the internal specifics of each one, you're probably still wondering what that all means when it comes to actually using binoculars.
Porro Prism Binnoculars
Physical difference: Porro prism binoculars, named after their 19th-century Italian inventor, can be recognized by the fact that the front or objective lens is offset from and not in line with the eyepiece or ocular lens.
Why you'd want it: This zig-zag design can provide a slightly clearer, more three-dimensional image with greater depth perception, and generally offer a wider field of view (F.O.V.), or the actual width of the sight picture at a specific distance.
Why you may not want it: They tend to be bigger, bulkier and heavier.
Roof Prism Binnoculars
Physical difference: In roof prism binoculars, the internal prisms overlap closely, allowing the objective lenses to line up directly with the eyepieces, resulting in an overall H-shape.
Why you'd want it: The design means a slim, streamlined shape, with less bulk and weight and perhaps a bit more ruggedness than Porro prism designs.
Why you may not want it: Although they may seem simpler on the outside, the internal workings of roof prisms are actually more complex than Porro prisms, making them more costly to manufacture, so they tend to cost more to buy.
Which is the best choice for you? Since their introduction in the '60s, roof prisms have become more popular, especially among hunters, but Porro prisms offer good value and performance and are still popular among birdwatchers and other recreational users. The best advice is to take a trip to your nearest Bass Pro Shops and try several options in your price range until you find one that fits your hands nicely. The ergonomics of these two styles are quite different, and what feels good in one person's hands may just not be right for someone else.