Features March 2003 Issue

Compact Binoculars

For onboard back-ups and excursions ashore, a set of good compact binox are almost required. Nikon fielded a strong team—their Mountaineers are a Best Buy. But the race is also to the Swift.

The uses of binoculars aboard a boat need not be explained in detail here. We know what they do: An indistinct lump becomes a buoy with a number; a smooth surface reveals a partially obscured rock; the figure waving to you from the dock isn't your wife after all. 

Top row, from left to right: Bushnell H2O 8x25, Bausch & Lomb 8x25, Canon 8x23 AWP, Leupold Wind River 8x23, Leupold Wind River 8x25. Middle row: Nikon Sportstar III 8x25, Nikon Medallion S 8x21, Nikon Eagleview Zoom II 8-24x25, Nikon Mountaineer 8x25, Nikon Travelite 8x25. Bottom row: Nikon Travelite Zoom 8-24x25, Steiner Predator 8x22, Swift 712 8x26, Swift Trilyte 802 8x25, Swift Micron 805R 8x25, West Marine Bora-Bora 8x26.

In the January 15, 1997 issue we evaluated a big field of binoculars ranging from 7 to 10 magnification, and in price from $50 to $805. This time we've limited the field considerably. Our criteria: compact, in the 8x25 range, preferably waterproof, and under $250. This subset fairly represents the kind of binoculars we would use as onboard back-ups, not only in case the primary specs fall overboard, but for times when the situation requires more than one set of searching eyes. These back-ups can be tossed into a backpack or bag and taken ashore for sightseeing, and in fact can serve as primaries in a lot of situations where you just need to grab a quick glance at something in the distance.

Bino-Basics
Binoculars are designated by two numbers: the first is the magnification, and the second is the diameter of the objective lens, in millimeters. The letter "x," as in "8x22," separates them and is pronounced "by," as in "Eight by twenty–two."

Like power steering and brakes, audio amplifiers, and even simple levers, binoculars are members of a general class that could be called effect multipliers. The first designation for a binocular is its magnification (the optical equivalant of leverage) , or how many times larger an object appears when seen looking through it, compared to using the naked eye.

As with all such devices, however, the laws of physics exact a price for the enhanced effect: in the case of binoculars this includes weight, bulk, eyestrain, optical distortion, blurred image due to operator movement, and darkening of the image. Sometimes the price is hidden, and this is surely the case with compact binoculars.To use the famous abbreviation coined by Robert Heinlein in The Moon Is A Harsh Mistress, TANSTAAFL: "There Ain't No Such Thing As A Free Lunch."

How Binoculars Work
A binocular consists of two parallel telescopes joined at the center by a hinge. The hinge allows the telescopes to be moved so they are exactly in front of the viewer's eyes.

A simple magnifying glass illustrates the basic optical principle. The glass is convex on both sides, and is called a converging lens. When light rays pass through the lens they are refracted (bent) toward the axis of the lens (this is how we use sunlight to start a fire). By putting our eye near the focal point (where the light rays converge) we see an enlarged image of the object on the other side of the glass —preferably not the sun. A somewhat more complex version of such a lens is used as the front, or objective, lens in each binocular tube. Its job is to gather light rays from the field of view.

The second designator of binoculars is the diameter of its objective lens, in millimeters. Thus, most of the binoculars in this review have objective lenses about an inch across.

Somewhere near the middle of each binocular tube the light passes through a prism. The prism serves two purposes: it produces upright (as opposed to inverted) images, and it folds the light path to reduce the length of the tube. Light then passes through the smaller eyepiece, or ocular lens, and enters your eye. In the eye the target of these rays is the retina, rich with endings of the optic nerve, which in turn is an extension of the brain. When the eye doesn’t focus rays exactly on the retina, information is lost. Lenses are prescribed and worn to correct such errors. Of course the brain itself isn’t passive, but instead processes the optic–nerve impulses in fantastic ways that are well beyond the scope of this article. Bearing in mind this basic explanation, now let's look at...

How Binoculars Vary
Lens glass doesn't perfectly pass all the light it receives; some is reflected away from the lens surface and is lost to the viewer's eyes. A microscopically thin coating of, for example, magnesium fluoride, on the glass surfaces can greatly reduce this light loss. In practice more than one coating is applied, because coatings are wavelength-sensitive. The relatively small-diameter objective lenses used in compact binoculars make lens multi-coating a must, in order to maximize light transmission. All the models in this report have coated optics.

A magnifying glass doesn't have a focusing mechanism: you simply move it to a position between the object and your eye where the image is sharp. One of the purposes of binoculars, however, is to magnify the object without moving either it or yourself; thus, the focusing must be done by moving lenses within the binoculars. Two methods are used: individual focusing of each tube, or center focusing where one control produces equal lens movement within each tube—the latter being obviously superior because it cuts focusing effort by half.

All the models here use center focusing. Focusing is accomplished by extending or retracting the length of the tube (external focusing) or by moving lenses within the tube itself (internal focusing). Here the latter technique—which all the models use—is also superior because it doesn't create positive or negative air pressure within the tube, which helps to introduce moisture into the tube. Some manufacturers fill the tubes with nitrogen, an inert gas, to inhibit condensation and bacterial growth; we note this feature in the table.

All serious binoculars provide a diopter adjustment—an additional focusing mechanism which allows one tube to be biased in favor of a stronger or weaker eye, so that one focusing position produces a sharp image in each eye. It doesn't matter which tube has the adjustment and, once adjusted for a given user, it's not changed. We discuss how to make this adjustment later.

We spoke of prisms above; there are two main types. Traditional binoculars, like the ones WW II submarine captains used, have Porro prisms, which allow the tubes to be farther apart at the objective (front) end than they are at the rear—very helpful when large objective lenses are used. Many modern binoculars employ roof prisms, which can fit within a straight tube and help reduce weight. We report on the types of prisms used, but bear in mind that each does basically the same job and neither is inherently superior to the other.

Leaving the insides of the binocular tubes, let's consider the outer surface. For nautical applications the tubes should be water resistant, and capable of surviving rough handling without denting. They should also have a non-slip surface. Rubber coating is typical. We note which models claim water resistance (and the specification, if any), as well as the kind of outer surface.

With compact binoculars it's critical to get the eyepieces close to your eyes—so you can use all the light that their relatively small exit pupil provides. This can be a problem if you wear glasses, so manufacturers usually make the outer layer around the eyepiece out of rubber that can be screwed down, rolled, or bent back so you can minimize the distance between the eyepiece lens and your eyeglass lens. All the models except the Bushnell have this feature.

Now let's leave the binoculars completely and deal with their cases. These may be soft or hard; they may close by zipper or Velcro device. The ideal case for our purposes would also be waterproof or at least water resistant. One very helpful feature that some cases offer is the ability to insert the binoculars without disturbing your alignment of the tubes: if it doesn't, then you have to realign them each time you take them out. (See table: "Maintain Tube Alignment?")

Read binocular warranties carefully. How long are both parts and labor provided for, versus only parts? Under what circumstances are the glasses warranted as water-resistant? In most cases the "lifetime" is yours, not the binoculars'. Do you have to do something special to qualify for warranty protection, like having the dealer fill in and stamp the warranty card—an unlikely event in a mail-order or internet purchase?

When we buy binoculars, it's not the piece of equipment itself that we want. It's the image produced on our retinas: thus optical performance outranks style, color, shape, accessories, and other lesser factors. Assuming its manufacturer has properly installed the various lenses and aligned the two tubes (which we didn't test), a binocular depends on such factors as these to produce that retinal image:

Lens Quality. Both the quality of the design and the quality with which the design is realized in a specific manufactured product. Opportunities for faults abound: distortion, chromatic aberration, spherical aberration, astigmatism, coma, flare, and vignetting are some of the terms used to describe them. We didn't test for these faults, but do report instances where a fault visibly compromises use.

Steadiness. Even a high-quality lens can't relay a usable image to your brain if it's constantly moving. The higher the magnification, the more the optic is sensitive to movement. Even heavy binoculars are hard to hold still; compact models are almost impossible—one way in which the lunch of portability is definitely not free.

Light-gathering ability. The function of the objective lens is to collect light and direct it to the prisms and ultimately to the eye. The larger the diameter of the objective lens, the more light available to enter your eye, thus providing a brighter and sharper image. The larger the diameter, however, the heavier and bulkier the binocular will be. A measurement called the exit pupil, calculated by dividing the diameter of the objective lens by the power (magnification) of the binocular, expresses generally the light-gathering ability of the binocular, in terms of the diameter of the shaft of light exiting the eyepiece. The larger the exit pupil, the brighter the image will appear, particularly in dim light.

When you use a pair of compact binoculars, one of the characteristics that you notice first is how small an image is produced in the eyepiece. An 8x24 binocular has an exit pupil equal to 24mm divided by 8, or 3mm, so you must get the eyepiece very close to your eye in order to see much. Is there a point at which an exit pupil would be bigger than your eye could use? Yes, if it's much bigger than your eye's scotopic aperture—the largest diameter of a dark-adjusted eye's pupil—about 6-7mm for people under 40; a little smaller if older. The ideal night glasses would have an exit pupil in this range.

The range of exit pupils among the evaluated binoculars is 21mm/8 (2.625mm) to 26mm/8 (3.25mm)—a difference of 0.625mm. This may seem insignificant at first, but now compare the area (pi times the radius squared) of the two shafts of light, since that's what's available to enter your eye—and you find that the larger exit pupil provides 53% more light than the smaller. That's a real, visible advantage.

Admittedly, none of these binoculars will excel at night viewing, but in daylight a greater exit pupil helps to compensate for the shake caused by light weight, by means of the larger area of light entering your eye. It doesn't cure the shake, but it mitigates its effect on what you can see.

How We Selected
We scoured both paper and Internet catalogues for models under $250 street price that seemed to have enough protection (from shock and water) to be useful on a boat. We know we missed plenty—there are more out there than we could reasonably test, or even find. But we ended up with 16 models, all 8x magnification, within our price range, and we'll look forward to hearing from readers about the pros and cons of binoculars not mentioned here.

How We Evaluated
We scrutinized each for signs of carelessness in design or manufacture. We didn't test, but simply report here, the manufacturers' claims for water resistance. Where provided, we use data from the brief page or two of information supplied by the maker. We scrutinized the exteriors for indications that would lower our confidence in water-resistance claims.

We used variations on eye-testing techniques to probe the binoculars' optical acuity. We used an eye-test target that had rows of upper-case letters from 9 point to 19-point type, plus rows of upper-case 9-point "E"s pointing randomly in all four directions. This was set up in direct afternoon sunlight, 64 feet away from the tester. Each binocular in turn was mounted on a heavy photographic tripod, which itself was out of the sun. Once diopter-adjusted and focused, the binocular was not touched. We rated optical performance according to the smallest row of letters read correctly, and for the percent of the row of "E"s visibly resolved.

While a few glasses did significantly better than others on this test, only one failed to resolve down to the 11-point level; most would resolve down to 10 points, and 10 models resolved 9-point type.

A second acuity test of all 16 pairs was run in another location by another observer, under similar conditions, but at a distance of 85 feet, with type from 32 down to 16 points, and without the tripod. The observation results were remarkably similar, although in the second test, binoculars that did well on the tripod were sometimes harder to steady by hand. The ratings in the table reflect both sets of eyeball evaluations.

Optical performance is only part of the story, however. In order to capture the rest we had to invent a couple of categories: Ease Of Use bundles together how well a model provides such mechanical factors as diopter adjustment, focusing, eyeglass accommodation, weight, attachment of strap, and even the case itself, especially whether it requires the binocular tubes to be folded in before insertion into the case: better than average (+), average (0) and worse than average (-) are the possible scores.

To augment raw optical performance, the "Transparency" rating attempts to convey how well the binocular "gets out of the way" and puts you in the scene you're watching: this includes brightness and clarity of image, perceived depth of field, field of view, exit pupil, and probably a few other factors—all rolled into one rating, from 1 (like looking through a keyhole) to 5 (maybe even better than being there).

We consider the kind and length of manufacturer's warranty important for a high-precision optic that's subject to both shock and water, and we included it in each binocular's Overall Rating, which summarizes claimed water resistance, optical acuity, ease of use and "transparency." The best were, obviously, those that were at the top of every category; and those at the top of three of four categories were designated next best.

Only after competing the evaluation did we look at each model's price. Thus, the chart ratings don't carry the connotation of "for the money."

The Binoculars

Bausch & Lomb 8x24 Legacy #12–0824. We experienced a bit of cognitive dissonance trying to figure out the origins of these binoculars. The old-line American brand name B&L is on the hardware itself, the box, and the instruction booklet, but they're sold and warranted by erstwhile competitor Bushnell—who, it also turns out, now also owns the old Tasco line of optical instruments. The binocular itself is made by an unknown third party in China.

Nonetheless, although the controls of these glasses felt less satisfying than most of the others, and the rubber coating had a dense smell (not just fresh out of the box, but continually), optical performance was numerically satisfactory. The image exhibited a milkiness at the edges that was absent in the top models.

Bushnell 8x25 H2O. These binoculars turned in a poor optical acuity score. They barely resolved one tester's maximum legible type size, and could not resolve maximum-sized type in the other test at all; nor could they get going in the E-test. The rubber eyepieces, normally designed to fold flush for eyeglass-wearers, were so short and stiff that they would not stay folded, and the case was difficult to work with. On the plus side, these were the least expensive units in the evaluation, are ruggedly built, and are warranted as fully waterproof.

Canon 8x23 AWP. These glasses embody a "Canon Optical Design" and are quite rugged...maybe even clunky. The case allows them to be inserted without collapsing the tubes, but the friction holding the interpupillary adjustment is a bit light. The objective lenses are commendably set back into the tube, farther away from spray, dirty fingers, or sharp objects. The strap brackets seem far more robust than those on some other models.

The optical performance, however, was merely good—maybe toward the excellent side of good, but it left this model farther from the top of the heap than we had expected when we saw the Canon name on the box.

Nikon 8x21 Medallion S #7378. This diminutive model appears to be little more than an opera glass. It performed well optically, but earned only a 3 in Transparency. Its short (3.7") length and light (8.5 oz.) weight are advantages—until it comes time to hold it still and see detail in an image that's floating around. Nikon has perhaps wisely given it a silvery color to help us avoid losing it. It has neither armor coating nor any claimed water resistance.

Nikon 8x25 WP/RA Mountaineer II ATB #7340. The second-heaviest model, this binocular was correspondingly easier to control, and impressed us with its optical clarity and acuity. Smooth central focusing added to ease of use. Its soft case accommodated the glasses without having to move the tubes together, judged a strong plus. With its all-metal construction and rubber armor, this waterproof model would appear more durable than others—and the manufacturer's 25-year warranty says much in favor of that being the case.

Perhaps a small point, but the instruction/specification booklets furnished by Nikon with all its models tested are far more informative and helpful than most others. Nikon is of course a famous manufacturer of cameras, a product with which more documentation is expected than with binoculars. This model was the best optical performer of the entire group, and with other good features easily merited excellent overall.

Nikon 8–24x25 Eagleview DX II Zoom #7326. That's right: a compact binocular that zooms—but if you've followed our discourse on exit pupils and binocular steadiness, you're probably sending out little mental probes asking, "Isn't the higher magnification produced by zooming paid for by even less light reaching the eye, thus making the image very difficult to steady unless the binocular is mounted on a tripod?" Why, yes, we couldn't have said it better ourselves. So, although these glasses share the same quality materials and construction as the other Nikon models tested, much of the advantage promised by the zoom feature won't be of much help in any kind of seaway. We estimate that 12x or as much as 16x could be used to spot some large, easily distinguished object from a boat, but from there on up expect the image to be oscillating a lot despite your best efforts. Given a stable platform (e.g. Mother Earth) the zoom feature has merit, but at the top power you're down to only 1mm of exit pupil.

Probably the most unusual design of all models tested, the Eagleview is wider at the rear, or viewing end, than at the front, a feat accomplished by locating the porro prisms near the front. Even when the tubes are adjusted for angle, the front lenses remain fixed. In addition, the zooming feature is activated by a lever embedded in the futuristic silver housing, just in front of the focusing knob. Eyeglass accommodation is provided by a convenient turn-to-retract eyecup.

One evaluator found these glasses jiggly and hard to focus in the non-tripod test. Optically, they were excellent at both zoom extremes. They're not water-resistant, though.

Nikon 8–24x25 Travelite V Zoom #7474. The comments above, regarding the Nikon Eagleview, apply to the Travelite as well, except that the evaluator who found the Eagleviews jiggly thought the Travelite Zooms easier to steady and focus. Although quite similar in optical quality to other Nikons in this report, this model does exhibit a few differences: Its tubes are an unusual futuristic shape (they bulge in the middle) and contain carbon fiber for strength; its soft case is metallic silver. The zoom control is similar in action to the diopter adjustment, but is mounted on the other tube. An excellent performer, but not water-resistant.

Nikon 8x25 Travelite V #7470. Essentially a non-zoom version of the Travelite model above, with slight differences in weight, field of view, closest focus, and country of origin (China). Performance is also excellent.

Nikon 8x25 Sportstar III #7458. This diminutive binocular has a field of view rated at 469 feet at 1,000 yards, the least powerful of the group. It did slightly better than the Bushnells in the optical tests, but is not armored or water-resistant. It's priced nicely, but we think these are best suited to stadium use, as the name suggests.

Steiner 8x22 Predator, #222. Easily the lightest and most elegant among the 16 models, the Steiner features extra-smooth center focusing and green rubber armor exterior covering tubes made of Macrolon. Despite its prestigious brand name, this model is too limited by its size, and by an extra millimeter or two of handicap in its objective lens, to approach the performance of the top models. Its case, the only semi-hard case among the 16, required the tubes to be folded before insertion, but was otherwise nicely fitted.

The Steiner name alone is tempting, but if you need truly compact binoculars that perform well, the Swift 712s, which weigh only 1.5 oz. more, would be a better choice.

Swift 8x26 #712. This smallish binocular did very well optically as well as in "transparency" and overall ease of use. Like the Bausch & Lomb unit, it suffered from smelly rubber armor. Its case is unique—it carries the glasses sideways, which we judge a definite plus, since it protects both sets of lenses better.

Swift 8x25 #802. Second heaviest in the group, this roof-prism model manages to look fairly slim. It was easy to focus and rated high in acuity, ease of use, and "transparency." Much of the tabular data on the Swift models, including the term of the warranty, had to be obtained from the company website, and even there we found contradictions.

Swift 8x25 #805R. Although this model did provide a sharp image, it was another that exhibited a slight milkiness or cloudiness, more pronounced at the image's edge. Overall, its controls were somewhat stiffer in use than the smoothest models. This was a step down in quality from the other Swifts tested.

West Marine 8x26 Bora Bora #2677771. One in a series of models named after the Society Islands, it exhibits good optical performance. Its focusing knob offers excessive resistance to turning. Its soft case is designed to retain the glasses rather than to release them easily when needed. In addition to being waterproof, they are claimed to be fog-proof and anti-snow, although what additional benefit the latter confers escapes us. The West Marine "No Hassle Guarantee" is standard equipment.

Wind River 8x23 #53534. Leupold is an American optics company with a reputation in the field of telescopic sights for rifles. It is apparently importing the Wind River Wilderness Optics line from China as a second label to its own first-label Golden Ring series.

Optical performance was not quite up to the best tested, and a slight cloudiness in the image brought its overall rating down. Still, it does carry a limited lifetime warranty from an established American optics company, and this helped the rating a bit.

Wind River 8x25 #53538. Close in appearance to the Swift 802, but less useful optically, these glasses did garner a high Transparency rating.

Conclusions
Among the water-resistant binoculars, we like the Nikon Mountaineer 8x25s, the Swift 712 8x26, and the Swift 802 8x25.The next-best category comprises binoculars with top ratings in all other categories but lacking water-resistance. In this case it's a Nikon sweep: Nikon Eagleview 8–24x25, Nikon Travelite 8–24x25, and Nikon Travelite 8x25.

Finally adding in cost, we can nominate the Nikon Mountaineer 8x25 for Best Buy. Within the next-best category the Nikon Travelite 8x25 costs 32% less than either of the zoom models, and could be considered a within-category best buy.

Note the importance of exit pupil in these compact models. The recommended models have the larger objective lenses and thus exit pupils.

Look over the various ratings and prices, and you may conclude, as we did, that price isn't a reliable guide to the quality of these models. Especially in the compact range, many attributes interact to produce a binocular that will perform well or badly according to your own needs. If you have a big crew, you might even decide you'd be better off with two sets of merely good binoculars for the same cost as one set of excellent Nikons or Swifts.

 

Also With This Article
Click here to view "Value Guide: Compact Binoculars."

Contacts
Bausch & Lomb, 800/334-8815, www.bushnell.com
Bushnell, 800/423-3537, www.bushnell.com
Canon, 800/828-4040, www.canonbinocular.com
Nikon, 800/247-3464, www.nikonusa.com
Steiner, 800/257-7742, www.steiner-binoculars.com
Swift Instruments 800/446-1116, www.swift-optics.com
West Marine, 800/262-8464, www.westmarine.com
Wind River (Leupold & Stevens) 503/526-5195, www.leupold.com

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