This guide resolves a heated debate in the binocular community. Learn the differences between roof and Porro prism binoculars to inform your next purchase.
If you enjoy spending time outdoors, whether hiking, hunting, birding, or sailing, you know the importance of keeping your binoculars handy. Using them is second nature, and you likely keep them strapped to your body or have them ready to go at a moment’s notice. They’re so commonplace in the sporting optics world that you might not even marvel at the scientific advancement which contributed to the binoculars hanging from your neck.
Binoculars are an incredible feat of engineering, and they’ve come a long way since the days of men of the renaissance like Galileo. We now have a firm understanding of how light and prisms work so that the world of optics is no longer a mystery. These advancements have also led to two main types of prism designs in the binocular world, the roof prism and the Perger-Porro prism.
As with any community, whenever there is an either-or product, you’ll find that debates on Internet blogs abound. However, it isn’t quite fitting to pit roof prisms against Porro prisms, as each has its advantages and disadvantages. Instead, it’s about having a conversation about which prism is best to meet your outdoor viewing needs.
Read this guide for crucial information on how binoculars work and why we can squash the roof prism versus Porro prism binoculars debate.
Bird’s Eye View Of Binoculars
Before jumping into prisms, it’s essential first to understand how binoculars work. The process of being able to see an image all starts with light. The images and colors that we see are a product of objects reflecting light waves. Each color has its unique wavelength, and when it reaches the lens of our eye, we register the object as red or green or purple.
Binoculars work similarly to our eyes, except they add in the complication of glass elements and magnification. In your binoculars, you’ll typically find two lenses, the objective lens, which is closest to the object you’re viewing, and the eyepiece, which is closest to the user’s eye. These are converging lenses, meaning that they bulge outward like your own eye. Binoculars and other optical tools use convex lenses because they gather light on one end and focus it on a center point. This is precisely what we require to see an image!
While this might sound simple, there is a significant challenge that stands in the way of you and magnificent views. Since convex lenses magnify images, once you start trying to sight objects at a certain distance, you will break the focal point and get an upside-down image. Think back to your elementary science experiments. When you hold a magnifying glass too far back from the subject that you’re observing, the image flips upside down. This effect would be quite a problem for glassing hunters or vigilant birders. You’re probably thinking now – that’s not how my binoculars work. And for that, thank your lucky stars that in the 1850s the world was introduced to binoculars with prisms.
The Beauty of Prisms
Prisms were first incorporated into binoculars thanks to Italian inventor Ignazio Porro in 1854. Now known as the Perger-Porro prism, these work pretty much the same now as they did in the 19th century. Nowadays, in each ocular tube, you’ll find two off-set prisms. As you view an object, it reflects light waves that reach your objective lens. Your objective lens converges these waves to a single focal point. The waves then refract off of the prisms in a zigzag pattern before meeting your eye to create an image.
The prisms are set so that as the light refracts, your image flips for the human eye to perceive it. This is why you don’t experience distortions to the orientation, even at high magnification. The science behind these prisms is relatively simple and easy to replicate and manufacture. This design has also been around for centuries, so it has been perfected for crisp, detailed images.
According to the University of Arizona, the roof prism design is nearly as old as the Porro prism. Some believe the roof prism design was invented as early as the 1890s, so there’s been plenty of time for advancements. In a roof prism design, each ocular tube has two prisms that line up neatly with the objective lens and eyepiece. Since you do not have the high-index refraction from the off-set layout in the Porro prism, roof prisms must be designed with excruciate precision so that the light refracts properly to produce a clear image. The NRA paints the best picture, describing this process like when water in a river meets a large rock it separates, but then comes back together.
Overall, prisms are fascinating, but all too often overlooked as they’re concealed in the body of your binoculars. The addition of prisms to binoculars also increases the focal length, which is part of why modern binoculars can be comfortably compact while still providing breathtaking views.
Why Does This Matter?
By now, you’ve probably already forgotten there was a debate at hand as you come out of the weeds I’ve just dragged you through. It’s important to know how these prisms work and interact with your binoculars because it sends the message that both designs are perfectly fine for a variety of uses. But just to satiate the binocular community, let’s dive into the pros and cons of each design.
The Pro-Porro Prism Argument
Some outdoor enthusiasts will swear by Porro prism binoculars, and that’s probably because this design was more common only a few decades ago. The Bushnell H20 Porro Prism shows the classic Porro design that might make you think of your grandad’s binoculars. Even today, most hobbyists might prefer a Porro design since they are cheaper. The advantage of the off-set prisms is that these binoculars are easier to engineer and manufacture. This translates into savings for the customer, and you can typically find high-end Porro prism binoculars for much cheaper than a comparable roof prism set.
You’ll also find that Porro prisms are generally a better deal than roof prism binoculars at the same price point. We’ll dig into why later, but mostly, for roof prism binoculars to be as useful, they need a special coating. Porro prisms provide amazing, natural views as is without any extra work. These prisms are well-regarded for their depth of perspective and bringing nature up close.
A myth you’ll often see on the internet is that Porro prism binoculars are always clunkier and more cumbersome than roof prism designs. This claim is unfounded, especially the Porro prism binoculars on the market, like the Vortex Optext Vanquish binoculars. These binoculars are incredibly compact and weigh less than some of the leading roof prism designs. Vortex Optics uses a reverse Porro prism design, so you reap all of the benefits, while only adding 12.7 ounces to your pack.
Raise The Roof For This Prism
On the other side, we have high-tech hunters and hikers that have made the switch to roof prism design binoculars. The key advantage of roof prism binoculars is they tend to be more compact and lighter than Porro prism binoculars. This is due to their prisms being aligned, rather than off-set in the ocular tube.
Although the engineering on these is more complex, when a company gets it right, the views are next-level. Many long-distance shooters and hunters prefer roof prism binoculars to Porro because they can handle higher magnification power while still providing exacting details. If absolute precision is a necessity for your outdoor hobby, it is worth saving up for a pair of roof prism binoculars.
The high cost associated with roof prism binoculars is not just due to the complexity of their design. Since the light travels in a more complex pattern, there is a higher risk of losing some light transmission. To combat this problem, high-end roof prism binoculars will apply a phase-corrected lens to ensure that you’re getting optimal brightness with no distortions. As you shop for roof prism binoculars, keep the Vortex Optics Diamondback. This is an elite set of binoculars that does roof prism designs the right way by including the necessary coating.
A myth you’ll hear about roof prism binoculars is that they are less durable than Porro prism binoculars. While this might have been true a few generations ago, many optics brands produce tough as nails roof prism designs. This Bushnell H20 Roof Prism Binocular set is a prime example of rugged construction that can withstand your travels. These binoculars are 100% waterproof and can endure being submerged in water. They’re also fog proof and built with Bushnell’s exclusive rubber armor and Soft Texture Grip so that you’re covered in the event of a slip or trip.
Getting Your Priorities Straight
Whether you buy Porro or roof prism binoculars, you’ll still be one step closer to the wild. However, once you know your priorities or what’s best for your outdoor activity, you’ll make the best choice for which pair you should purchase. Here’s a short list of considerations to narrow down the binoculars you have in your Amazon cart.
If you’re looking for budget-friendly binoculars, nine times out of ten, you’ll want to go with a Porro prism design. Even if you find a pair of roof prism binoculars at the same price, they might not be as high-quality. Double-check the brand and if they use a phase-corrected coating. If those roof prism binoculars don’t check out, go with the Porro prism design instead. Models like the Bushnell H20 Porro Prism, with its 50 mm objective, will give you fantastic, in-depth views for under $100. Bushnell’s H20 Roof Prism binoculars also come in at just over $100 but do not seem to have a phase-corrected coating.
Compact & Lightweight
Roof prism designs will be your best starting point for lightweight, compact, and easy to hold binoculars. While you can find Porro prism binoculars that are just as compact, the majority are not. The Vortex Optics Diamond, with its roof prism design, weighs 21.8 ounces. This is even with a relatively large 42 mm objective lens. The middle hinge allows these binoculars to fold up neatly so they can fit in the pocket of your hiking pants or comfortably in your hands. As mentioned, the Vortex Optics Vanquish binoculars are also extremely compact and would be great for hiking. Their objective lens is significantly smaller at 26 mm, so you will experience less light-gathering capacity.
Best for Long Distances
The Vortex Optics Diamondback is hands down the best optical tool for long-distance hunters and shooters. It is a roof system design with a phase-corrected coating. The lenses are also dielectric and fully multi-coated for the best possible light transmission. The focal length is increased with the roof prism system and makes for better, detailed images. You can also follow fast-moving targets and prey easily at high magnifications.
All You Need Is Prisms
It is important to know how prisms work and the inherent differences in each type of design so that you can make an informed decision about which binoculars are best for your purposes. Instead of comparing side by side, understand how each prism impacts the price, build, and quality of your image. The roof prism versus Porro prism debate can fade into the darkness of the internet blogs. Then, we can all agree that having high-quality prisms is really what matters for your binoculars to work their magic.
As you shop around, check out the binoculars mentioned in this guide. There’s a mix of both roof and Porro prism designs so that you know no bias went into the making of this article. These will give a good baseline for well-regarded brands and binoculars. With this knowledge, though, you’re in good hands to confidently make your purchase.