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Types of Binoculars

Posted February 4, 2009 @ 5:13pm | by TravelWild

When it comes to choosing items to bring along on a cruise to Antarctica or the Arctic, one of the true “essentials” is a pair of quality binoculars.  Arriving on my first Spitsbergen cruise without a pair of my own, I quickly learned how much there is to be gained by having binoculars as I borrowed pair after pair from fellow travelers and trip leaders.  How embarrassing to be the TravelWild office representative and not have brought my own binocs.  Never again!

Perhaps the only benefit of borrowing so many pairs of binoculars is that it gave me the opportunity to try out a number different pairs and learn how they compare.  Up to that point, I considered binoculars to be, well, binoculars.  Beyond magnification, I hadn’t given a lot of thought to the factors that make a good, useful pair of binoculars.  But, as I tried out at least a dozen different pairs, it quickly became clear that there’s a lot more to binoculars than simply magnification.

Myself notwithstanding, most people inherently understand the benefits of bringing a pair of binoculars on a nature and wildlife trip.  What may not be as obvious to many are the different types of binoculars and their various features, advantages and disadvantages.  In this post, I will cover the different types of binocs available.

There are two types of binoculars, Porro prism and roof prism.

Porro prism binoculars utilize right-angle prisms in each of a binocular’s two barrels.  These prisms reflect, or bend, the light on its path from the subject to your eye.  When they were invented, they allowed for a smaller, more compact unit than the common alternative of the day, telescopes.  The main advantages of Porro binocs are that they allow in a substantial amount of light—the more light, the easier it is to see your subject—and, compared to roof prism binocs, they offer a wider angle of view and can be focused faster and closer to your subject.

One disadvantage of Porro prism binocs is that they tend to be relatively heavy and bulky as compared to roof prism binocs.  Additionally, over time, normal wear and tear of using these binocs in the field—an occasional drop, stowing them in a backpack that gets tossed around, etc.—can cause the prisms to go out of alignment making images appear distorted.

A good pair of Porro prism binoculars typically costs $100-$300. When shopping for Porro prism binoculars, we strongly suggest you buy a pair with center focusing.  Center focusing binocs allow you to simultaneously focus both eyepieces—much easier than using binocs that require each eyepiece to be focused independently. 

Roof prism binoculars get their name from the system of prisms—typically five of them—located in each barrel.  The arrangement of these prisms is said to have resembled the shape of roofs found on late 19th-century German houses.

The primary advantages of roof prism binocs is that they are lighter and smaller than Porros.  Their shape—which roughly resembles the letter “H”—also makes handling them easier than the bulkier, M-shaped Porros.  Roof prism binocs also tend to be more durable due to the fact that most of their focusing mechanism is internal and therefore better protected from the elements.

The down side of roof prism binocs is that the 5-prism system causes a slight loss of light, so images will often appear slightly darkened.  Furthermore, these binocs don’t focus as closely to your subject, which can be frustrating.  They also tend to cost more than Porros—typically $250 – $1,000.  There’s a price to pay for a smaller, sleeker, more-durable set of binoculars!

Both Porro and roof prism binoculars now are available with image stabilization. You may already be familiar with image stabilization—many digital cameras and  camcorder have this useful feature.  As a general rule, image stabilization adds to the weight, size and cost of binoculars.  You will want to try pairs with and without this feature to decide if it’s worth the added cost and weight.  If you’re shopping for binocs with very strong magnification, give additional consideration to image stabilization as the stronger the magnification, the harder it is to hold binocs steady.

And, finally, we come to magnification—the feature most of us are familiar with.  While most people understand that the stronger the magnification, the “farther” you can see (or “closer” a subject is brought to your eye), they often aren’t familiar with the way magnification is referenced.  Binoculars magnification is usually represented with two numbers, such as 7×35 or 10×40.  The first number indicates how many times a subject will be magnified by the binocs.  For example, when using 7x binocs, a distant object will appear 7 times larger through the binocs than it does to the naked eye.  The second number represents the diameter of the objective lens in millimeters.  As a rule, the larger the objective lens, the more light the binocs will let in, thereby making it easier to see your subject.

That covers the basics on types of binoculars.  Check back for a future post on using binoculars or, better yet, subscribe to our email updates and you’ll automatically receive notification when new posts are added (usually a couple each month). 

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