Choosing the right optic equipment for your chosen activity is essential. Even more so if you plan to be out in harsh weather conditions. Understanding how binoculars and telescopes are sealed against the elements can help you make the right decision about what kind of optic you need. It can also help you care for them properly to ensure years of use and proper function. Is just choosing a waterproof pair enough? Does it matter which gas is used to fill the barrels? Find out before you take that next hike in the rain.
Whether the activity is bird watching, hunting, hiking, or any other outdoor activity, the gear used must be able to endure the elements. From the cold rain and snow of a northern forest, to the blistering heat of a southwestern desert, to the humidity of a tropical jungle, any equipment taken on the trip must be able not only to withstand the conditions encountered (including accidents), but also function properly despite them as well. For boots, packs, and other gear, this is pretty straightforward. Sophisticated optical instruments such as binoculars and telescopes rely on a number of fragile glass lenses placed in very specific positions. How can they be protected against all the bumps, jolts, humidity, rain, dust, dirt, and changes in both atmospheric temperature and pressure without interfering with their ability to function?
The answer to this question can be summarized by two key words: “fit” and “seal.” While reams of paper and gigabytes of Web site space have been devoted to the variety of environmental protective measures employed by binocular and telescope manufacturers—armor, hard coating for lenses, nitrogen/argon purging, and others—none are particularly effective if the designers and assemblers did not pay sufficient attention was to the proper fitting of the component parts, and the effective sealing of joints.
In binoculars or telescopes designed to withstand harsh environmental conditions, the proper fitting of all the component parts is crucial and begins at the very first stages of the instrument’s creation. Tolerances (the allowable margins of physical variation by which a mechanical part can be manufactured and still work properly) as close as 1/10,000th of an inch are sometimes required to ensure the instrument’s effective long-term performance. Lenses and their associated holders (the machined parts into which the lenses are fitted) must not only be fitted precisely in order for the entire optical system to work, they must be kept there without slipping, rotating, or changing position in any way, even after being bumped, dropped, or subjected to rapid changes in temperature or pressure.
In addition, precisely fitted mechanical parts are more resistant to breaking—especially parts that are designed to move regularly, such as those that make up the focusing mechanism in binoculars. With poorly fitted parts, constant movement over time will gradually grind down the part’s material, weakening it and increasing the chance that it will either break or compromise a seal. In fact, without closely fitted parts, effective sealing—the second crucial element to environmental protection—is very difficult, if not impossible to achieve.
Because optical instruments such as binoculars and telescopes are designed to present their users with a magnified view of objects, their lenses naturally show an enlarged view of anything seen through them. This includes dust, dirt, and other seemingly tiny particles that might accidentally find their way inside the optical path of the instrument. When caught between the many lenses that make up a single optical path, even a grain of pollen or a speck of dirt can seem like a boulder in the field of view. Such undesirable objects, particularly dust with a high mineral content, can also shorten the lifetime of moving mechanical parts if they find their way between them. Think sandpaper and the reason will be perfectly clear.
Seals are not only created to keep unwanted material out of an optical instrument, but to keep desired substances, particularly gases, inside them as well. Marcus Leupold and his team of engineers at Leupold & Stevens created the first effective nitrogen-filled optic back in the early 1940s as part of a U.S. military project to build targeting sites for high altitude U.S. bombers. Since then, the method of effectively sealing optical instruments has been an essential element in their design. Ambient air, which contains both oxygen and hydrogen, is removed from binoculars’ or a telescope’s internal space, and replaced with an inert gas such as nitrogen. If the instrument is exposed to a rapid change in temperature—for example, from moving outside from a warm cabin on a cold, rainy day—condensation will not form inside the optic instrument, and the view will not be fogged. Should internal fogging occur, it will not only reduce the effectiveness of the instrument at that time, it will leave water spots on the lenses that will be magnified, reducing clarity and obscuring portions of the visual field.
Once fit and sealing have been addressed, there is a range of additional features that can be added to a binocular or telescope in order to improve its overall resistance to harsh conditions. Shortening the overall length of the instrument can offer structural advantages against bumps and falls. A short, squat object is likely to be more durable than a longer, thinner one. External armoring, where the instrument is coated in a layer of durable rubber or other material, can also help to protect it against physical impacts. Particularly effective armor is enhanced in areas of likely impact should the instrument be dropped, such as at corners, and particularly around the objective lenses.
As for lenses, new coatings to protect against scratches and external condensation are constantly being developed. While many such coatings have been developed and proved highly effective in laboratories, they must not interfere with the optical performance of the instrument. Because of this, many have never been released to market as they were shown to distort the visual image by adding unwanted colors or decreasing light transmission. Incidentally, don’t look at the objective lenses of a binocular or telescope for proof of one type of coating or another. The colorful, reflective sheens seen on the objective lenses of many optical instruments are a result of their particular construction or coating type.
Even with protective coatings, keeping external lenses free from dust, rain spotting, and scratches requires good lens covers. Binoculars and telescopes designed for harsh conditions are sold with effective covers to protect the lenses at all times when the instrument is not in use. Case covers, the simple plastic disks that fit loosely and fall free as soon as the instrument is removed from its storage case don’t count. Good field lens covers will stay in place while the instrument is being carried, and even remain tethered or otherwise connected to the instrument while actively in use.
So who makes the optical instruments that satisfy all these conditions? There are many fine manufacturers of binoculars and spotting scopesthat produce and sell products well suited to harsh conditions. Go on a birding trip to Panama, a hunting expedition to Africa, or a trek up one of the many great mountain ranges of the world, and you will no doubt see your colleagues toting a Swarovski, Zeiss, Leica, Nikon, or Leupold binocular, and with good reason. But when it comes to over-the-top design intended to protect the structure and operational integrity of their binoculars, one name is particularly well regarded, so much so that they are the primary binocular supplier to military and law enforcement organizations around the world: Steiner. Whether the popular Merlin or Peregrine product groups, the innovative Wildlife Pro series, or the new high performance Predator C5 models, users will find each to be a remarkable combination of superior optical performance combined with military standard, and the ability to withstand the elements.
Not everyone needs military specification binoculars for everything from physical impact to underwater submersion, but if your purpose for the optic is a once in a lifetime trip, over-preparedness is never a bad thing. Over the past decade, market forces have pushed all the upper-level manufacturers to include features that allow their products to withstand harsh conditions. Keep these features in mind when making a selection, and choosing the binoculars or telescope with the appropriate level of environmental protection should not be a difficult task.