Roof Prism vs Porro Prism Binoculars: 18 Main Differences

Roof prism vs Porro prism binoculars – which is better? And are the differences that important when it comes to quality, comfort, and overall enjoyment?

The most obvious difference between Roof prism vs Porro prism binoculars is visual:  the sleek and elegant housing of the Roof prism binocular, vs the bulky zig-zag aesthetic of the Porro prism binocular due to its widely spaced barrels.

I first saw Porro prism binoculars when I was a kid living in NYC.  My friend’s father decided to spend his Saturday birdwatching in upstate NY and let us climb into his old red Volvo so he’d have two chatterboxes to talk to on the longish drive. 

I clearly remember watching him use his Porro prism binoculars, and wondering why they were so funny looking.  That was the day I found out that there were two types of binoculars.

The shape of both Roof and Porro prism binoculars is determined by the alignment of their prisms.  There are numerous other differences between Roof and Porro prism binoculars as well. This article will explain the differences in language a beginner can understand.

Roof Prism vs Porro Prism Binoculars – How They Differ

Here is a quick summary of the 18 differences between Roof and Porro prism binoculars.

Here is a great video that discusses the differences between Porro and Roof prism binoculars.

I’ve also provided a bit more detail about the differences between Roof prism binoculars and Porro prism binoculars below.

Image Clarity and Light Loss

The subject of internal reflections plays a major role in image clarity and light loss. Porro prisms provide an extra clear and bright image since, due to the construction, there is less light loss – when light waves enter the prism there is total internal reflection.

Depth Perception

It turns out that the wider spacing of the Porro prism binocular objective lenses results in a slightly stereoscopic three-dimensional image, providing the user with increased depth perception. (However, some users feel that the Roof prism binocular gives a more “accurate” view and that the 3-D Porro prism effect is slightly exaggerated).

Field of View

Porro prism binoculars offer a wider field of view, meaning that you can see more of the image from left to right. This makes it easier to spot or scan for wildlife without moving the binoculars since you can see more at the outset.

Cost

Porro prism binoculars are generally quite affordable since they are cheaper to manufacture. Porro prism binoculars, when compared to Roof prism binoculars, give a lot of bang for the buck. They definitely have their fans!

The sophisticated maneuvering of the light path that a roof prism setup provides is impressive and, not surprisingly, comes at a higher cost.

Tripod Mounting

You will find more Porro prism binoculars that can be mounted onto Tripods.

Shape/Compactness

Roof prism binoculars are more streamlined, compact, and lightweight, while Porro prism binoculars are bulkier due to the wide spacing of the two barrels and their awkward overall shape.

This is because, unlike the Porro prism binoculars, the placement of the 2 internal prisms does not require the offsetting of the objective lens and eyepiece. Instead, they can be aligned, resulting in a sleek profile.

The shape of Porro prisms makes them awkward to hold, especially for smaller hands.

Ergonomics

The Roof prism binocular has a more streamlined shape and has a definite ergonomic advantage, as it’s easier to hold than the bulky Porro prism binocular, and also lighter in weight. Porro prism binoculars are not as comfortable to hold due to their wide shape and heft.

Eyecups

Roof prism binoculars have superior eyecups since most are twist-ups with multiple settings! For eyeglass wearers, this is one of their most important purchasing criteria since they can then fully or partially retract the eyecups to increase eye relief.

In contrast, Porro prism binoculars mostly use fold-down eyecups which can only be set at 2 positions – up or down.

Weight

Roof prism binoculars are lighter, while Porro prism binoculars can start feeling heavy on long bird-watching adventures.

Availability/Selection

Over the past several years, Porro prism binoculars have been phasing out, with fewer manufacturers making them.

Other than being used on larger binoculars designed for astrology, and binoculars meant for water use and low light, they are not as prevalent as Roof prism binoculars.

Popularity

Roof prism binoculars are generally more popular than Porro prism binoculars – you will see way more of them out in the field.

Technological Advances

Since Roof Prism binoculars are so popular, Roof prism technology continues to be refined. For example, you can now get Roof prism binoculars with a wider field of view than you could in the past.

In addition, the higher-end Roof prism binocular models have optical qualities that are equal to that of a Porro prism binocular.

Durability

In addition to their ergonomic benefits, and light weight, Roof prism binoculars are more durable than Porro prism binoculars, and also have better waterproofing.

Porro prism binoculars can easily become misaligned if they are dropped. This is due to their internal design.

Waterproofing/Dustproofing

Due to their construction, Roof prism binoculars are much easier to waterproof. Porro prism binoculars are sealed with “o” rings and, over time, the seal can become compromised. When this happens, moisture and dust can make their way into the interior.

Magnification

With Roof prism binoculars, you can obtain greater magnification due to the roof prism binoculars longer focal path.

Roof and Porro Prisms – The Science

Learning about the optical science behind Roof and Porro prisms in binoculars will hopefully heighten your interest and appreciation of the internal workings of binoculars.

Let’s start with the basics – what is a prism… and how do prisms work…

Think back to junior high school. Do you remember watching your teacher shining a light through a triangular block of glass to demonstrate the concept of dispersion? As the white light entered this prism, it exited as a spectrum of colors, casting a rainbow on the wall.

The prism used in that demonstration was a dispersive prism. In contrast, reflective prisms, instead of dispersing light, reflect it.

Let’s take a look at the world of reflective prisms: specifically, Roof and Porro prisms in binoculars, and why binoculars with Roof prisms are a better bet for bird watchers who wear glasses.

Reflecting prisms are perfect mechanisms for flipping and inverting light. And it turns out that this type of transformation is particularly useful when it comes to binoculars.

How Do Binocular Prisms Work? Flipping and Inverting Light

If you could look inside each of the barrels of a binocular, beyond the optical lens, you would see two prisms, placed at right angles to each other. The interplay of these prisms plays a critical role that impacts both the image you see and the size of your binoculars.

First, you might not know that when light enters the large optical lens, the image formed is actually turned upside down and also horizontally flipped from right to left.

As the light, and the altered image, make their way further down the barrel and begin to transit through the two prisms, the prisms work together to turn the image right side up and to also flip the image from left to right.

Shortening The Light Path

In addition to correcting an upside-down inverted image, if it weren’t for prisms, our binoculars would be much longer and unwieldy. Imagine zooming in on a hummingbird garden or a Mallard duck floating across a pond while carrying a half-meter-long piece of equipment around your neck!

Without Roof and Porro prisms in binoculars, in order to achieve the magnification of modern prism binoculars, the interior of the binocular would need to consist of a long series of lenses, placed one after the other. This is because light needs to travel a specific distance in order to significantly magnify an image and also provide a wider field of view.

So, how do you physically reduce the length of binoculars while still maintaining a relatively long path of light? You guessed it – through the use of prisms. This is how it works…

Think of the light path as a piece of a string having a certain length. The string is the same length whether it is laid out in a straight line, or whether it bends in different directions.

Two prisms will work together, reflecting and bending the light, so that it fits into a physically smaller space.

Without the prisms, a smaller binocular could only accommodate a shorter light path.

So, in effect, in a smaller binocular, prisms lengthen the distance of the path of light by bending it, reversing its path a number of times, as it transits between the objective lens and the eyepiece.

Roof and Porro Prisms – How Optics Drive the Designs

Porro prism binoculars are easy to spot due to their interesting, non-linear shape. This wasn’t a stylistic decision but was driven by a combination of optics and spacing constraints.

The shape and placement of these prisms constrain the placement of the eyepieces and objective lenses – instead of placing them one behind the other, they need to be offset, resulting in a wide spacing of the objective lenses and an interesting zig-zaggy external shape.

Unlike the Porro system where two identical Porro prisms are combined, Roof prism binoculars actually combine one auxiliary half-Penta prism and one Roof prism (shaped like the roof of a house).

When light enters the objective lens, as the light transits through the prisms its bent multiple times to shorten the optical path.

In addition, its bent in such a way that the light that is entering the objective lens and exiting from the eyepiece is on the same plane. This decreases their width and size when compared to Porro prism binoculars.

Roof and Porro Prisms – The History

It turns out that the history behind Roof and Porro prisms is actually quite interesting.

Porro Prism History

Porro prisms are named after the Italian engineer who invented them in the 1800s – Ignazio Porro. They were considered the first modern binoculars. At the time, he was not recognized for this incredible invention. He was also not financially compensated.

It was only after his death that Porro’s contribution was recognized and his name became widely known. In fact, when Ernst Abbe tried to patent an optical prism system decades later, he was amazed to find that someone named Porro had already patented the same design in 1854.

Porro found that by aligning two prisms so that they faced one another, touching along their longest surfaces, he could significantly decrease the length of the optical path.

This invention caused quite a stir since it significantly reduced the size of binoculars used in the 19th century, and so increased their use. The Carol Zeiss company improved on this design in the 1890s.

Roof Prism History

As much as the earlier users of Porro prism binoculars appreciated their relatively compact size, they wanted something even smaller. This desire gave rise to the invention of Roof prism binoculars.

Roof prism designs appeared on the market in 1897. In 1899 the Schmidt-Pechan prism was invented, which is what most modern Roof prism binoculars use today.

A few years later, in 1905, the Abbe-Koenig prism was invented, named after the inventors Ernst Karl Abbe and Albert Koenig. Again the Carl Zeiss company was involved and held the patent.

Final words on Roof Prism vs Porro Prism Binoculars

So now you have learned about the differences between Roof and Porro prisms in binoculars, as well as the science and history behind them.  Which one will you choose? 

In summary, Porro prism binoculars offer a wider field of view, a slight 3-D stereoscopic more realistic image, and are less expensive than Roof prism binoculars. However, they are less durable, bulky and so harder to hold, and heavier. Lastly, you can only get them with folding eyecups.

But… some people do love them. There are many Porro prism binocular owners that wax poetic about their binoculars.

As for Roof prism binoculars, their streamlined shape and lighter weight make them easier to hold and carry than Porro prism binoculars. In addition, they are more durable, have better waterproofing, and have twist-up eyecups. Optical qualities in more expensive models are excellent.

If you wear glasses and are looking for the best binoculars for viewing birds and wildlife of land and sea, then Roof prism binoculars should meet your needs very well.

If you hunt, on the other hand, and want binoculars with the widest possible view to allow you to easily scan for wildlife without having to constantly move the binoculars, don’t mind the extra heft and weight, perhaps have larger hands… you might want to consider Porro prism binoculars.

In fact, some birders I know actually have a collection of binoculars that include both Roof and Porro prism binoculars, love them equally, and use them for different occasions.

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