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Are Roof Prism Binoculars Superior to Porros?

Roof prism binoculars are all the rage (and so is their outrageous pricetags) but are they really better than porro prism binoculars?

By Jeff Johnston

The Myth
Are Roof Prism binoculars are superior to Porro Prism Binos? You’ve probably seen most of the hunting shows and read the magazines, where most of the professional (and sponsored) hunters use top-quality roof prism binocular from such optical firms as Zeiss, Swarovski and Nikon
. You’ve probably also seen your known cheapskate buddy Bob using an old, gigantic Porro prism bino (those that do not have two straight ocular barrels like roof prism binoculars) and quickly deduced that Bob’s is cheaper than Joe Professionals unit and therefore inferior. After all, we’ve been writing that “you get what you pay for in optics” for years, and certainly, on average, Porro prism binoculars are less expensive than roofs.

But I want to know if Porro prism optics really are inferior.

The Expert Deferral
I could go outside on a dark day and compare 50 sets of Porro prisms and 50 roof prisms, but you wouldn’t learn much. It’s best to consult the experts who know the engineering—and marketing—behind the rubber armor to best answer this question. There are few people more qualified on this topic than frequent American Hunter optics and gun writer, John Barsness. He’s been a hunter longer than most Indian tribes, and he’s literally written the books on optics for hunters. It’s called, “Optics for the Hunter.”
For the answer to the Porro vs. roof prism question, I’ll draw heavily from Barsness’ book, rather than reinvent the wheel.

The Physics
Optics benefit from focal length. That’s why powerful telescopes and even riflescope are physically long. Generally the longer the better especially where high magnification is concerned. But a hunter can’t easily toss the Hubble telescope on a dashboard. Porro prisms (named after Italian inventor Ignazio Porro) have adequate focal length for sporting applications yet remain compact enough to easily hold in the hand. They do this by utilizing two glass prisms in each barrel to bend the image (light) from the target to the eye in a simple figure that resembles the letter z. All surfaces of the prisms are reflective, so they lose no light in the process. This prism configuration necessitates that each barrel be shaped like a dog leg to accommodate it, which makes them slightly bulkier.

A roof prism utilizes two glass prisms to bend light via a complex pattern (in order to make it compact) and split it into two halves, where it eventually flows back together before reaching the eye. To borrow one of Barsness’ analogies, think of it like a rock in the middle of a stream. Water flows toward it, splits at the rock, then flows together again. However, when it flows back together it does not perfectly meld (or “phase”) back in—instead it has ripples and aberrations. A special, costly and relatively new process called “phase correction” must be applied to roof prisms to ensure crisp images. Also, roof prism designs are much more complicated and require precision manufacturing techniques to build them well. Lastly, one surface of the roof prism is not 100-percent reflective, so anti-reflective coatings must be applied, but they can never have 100 percent light transmission. This is why roof prisms are inherently tougher to manufacture. It’s also why they are inherently more expensive than Porros.

The Short Answer
Generally an inexpensive Porro prism binocular is better than an inexpensive roof prism binocular.

The Obvious Question
So why, then, are roof prism binoculars so popular?

Because people like compact things they can most easily transport, roof prisms offer an inherently more compact ocular system. So, in their quests to build the perfect binocular, a couple decades ago top optics companies such as Zeiss focused their best engineering and technology into creating a compact roof prism binocular that would perform optically alongside the best Porros. Trouble is, these binoculars cost hundreds if not thousands of dollars to produce. So, for years, if you wanted a compact roof prism of best optical quality you had to shell out huge money.

Since then, computer manufacturing techniques and trade secrets have been passed to far eastern companies that can produce wonderful optics at a fraction of the cost of the German juggernauts. Plus, most of us want to be like Joe Pro rather than Bob Cheap-O. So we demanded decent roof prism binoculars. Fierce competition, along with updated manufacturing have driven prices down. Now you can get a good roof prism for about $400 bucks and up. But if they are cheaper than that, many times companies must skip important steps in the process—just to sell an expensive-looking binocular at a competitive price.

The Bottom Line on Binos
If a company put all its resources into a Porro prism binocular, it would be at least as good as a roof prism, if not better. But it would be bulkier. With components and labor efforts being equal, Porro prisms are superior. But like most things in life, the reality is all things aren’t equal. Companies do not put all their resources into Porros because the public wants compact roof prism binos. So, if you want the best bino available, pay a couple thousand dollars for the best quality roof prisms. But if you have less than about $400 to spend, look hard at a Porro prism binocular from a reputable company.

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4 Responses to Are Roof Prism Binoculars Superior to Porros?

franek pudlo wrote:
November 16, 2012

I own a 3 pairs of different porro-prism (conventional) binoculars, the most powerful being 20x60. Upon buying an inexpensive, but still acceptable quality, roof-prism pair (10x25), the first thing I noticed is that there is objectionalble glare when aimed in the direction of a light source (e.g. towards, but not at, the setting sun). I thought this was a compromise of the manufacturer (imported by Celestron) but now I believe that it is a characteristic of the roof-prisms in general. Accepting this, they are extremely compact and portable and therefore appreciated in spite of this limitation.

binocular accessories wrote:
November 05, 2012

Hi all.... i would like to share certain things regarding the different models of binoculars....Have got one model of pentax papilo brand of binocular which it has a high refraction and shows very large image even if it is smaller one...It is mostly suitable for treking,hiking etc...So, i like enjoying viewing images through using this kind of binoculars.

WCoyote wrote:
October 25, 2012

Extremely interesting and informative article. Like a lot things the world of binocular technology and manufacturing is changing at a rapid pace. The improvements in glass quality, engineering and manufacturing processes is truly amazing. The cost of high end binoculars is, well still high. The big difference today is that several hundred dollars will get you a really, really good binocular for hunting activities of all kinds. Not that long ago this amount would by only so, so binocs. Most companies have offerings that include very, very hunting optics at $400-$600. We have used some of the new BX-3 Mojaves from Leupold and they are amazing from the quality of optics stand point and also from the their price point as well. Again article. <A href="www.wcoyoteoutdoors.com/Leupold-Binoculars.html">BX Binocular</A>

Pete wrote:
October 22, 2012

I was in the retail optical business for over 31 years. When Bausch and Lomb, which started about 1853, made binoculars, they were the best in the business, even with Zeiss around. Unfortunately, they are gone now, but, they were known world-wide, and were prized.