Binocular purchase: Collected wisdoms

by Holger Merlitz

Over a period of 6 years I have been scanning the binoculars markets. During that time, I have purchased more than 100 instruments, the majority of them as second hand items, many of them sold again. The more interesting items had to undergo a careful test procedure, leading to these comparative test reports which are found somewhere else on my web-site. Also, a few binoculars were provided exclusively for testing by vendors who were keen on seeing their products being compared in my reviews. With their support I was able to extend the performance spectrum of my test-candidates towards the high-end region.

The selection procedure for my survey was naturally biased to rather easily available items on the European and especially on the German market. If one compares the offerings on Ebay Germany with Ebay US, it immediately becomes clear that the subset of binoculars frequently found on both of them makes less than 50% of the total. It doesn't need much of investigation to realize that my selection contains an un-proportional high number of Porro type binoculars, many of them being military instruments and quite a few of them being of East European origin. This reflects my personal focus of interest, of course, however - just in parts. Actually, this is also a natural result of a selection procedure, driven by the desire to optimize the price-to-performance ratio. In the following remarks I shall frequently come back to the most essential question of every binoculars user: How could I find the maximum performance for my needs and for the money I am willing to spend?

Wisdom No. 1:

There are no usable binoculars for less than 50 Euro/Dollars

Optical instruments do not only require a high precision optics but also a mechanical framework which keeps the construction in proper collimation. A handheld binocular is not a stationary device, but carried around and thereby taking mechanical and thermal stress and still having to keep its internals fixed on a scale of a few hundreds of mm. This can't work out for a few bucks, neither in China nor anywhere else around the world ("you cannot make a Rolls-Royce out of steel wool by just adding water", Bill Cook on Cloudy Nights). The huge amount of 'night-active', 'ruby-coated', camouflage painted plastic binoculars offered on Ebay for 20 Euro or less are complete rubbish and not even worth to be considered as a toy for the kids. The cheapest binoculars which satisfy the minimum requirements of delivering a sharp image within 50% of the field and which come with a body where at least the prism housings are made of metal are found in the 50 Euro region. Ok - a few Russian binoculars are there for somewhat less. But although these are usually made of metal and sometimes even come with a reasonable coating, their state of collimation seems to be a random variable and it sometimes needs to order a couple of them before finally having one of proper performance. While the low-end Chinese binoculars are useless, their middle range, as sold for 50 Euro and above, comes with a mechanical construction which is often superior to the Russian glasses of same price. However, they are often lacking in their quality of coating and tend to produce excessive ghost images of bright objects.

Wisdom No. 2:

If a binocular has to be rugged and cheap, look around for (second hand) military devices

In most cases, such a military binocular is of Porro type with individually focusing oculars. This type of construction is comparably simple and therefore cheap, and the individual focuser allows for a much easier sealing against environmental hazards (dust, humidity) than any standard central focuser. In recent years some cheap "water proof" Porro binoculars with sealed central focuser have shown up, but, as a side-effect of the sealing, they sometimes focus inaccurately and do not deliver sharp images. Roof prism binoculars usually come with internal focuser and are easier to seal up, but are generally of higher price for a given optical performance. A military binocular provides a fairly decent optical performance and has been tested to survive a considerable amount of mechanical abuse. The smaller versions of them, typically of 8x30, are found on Ebay from 80 Euro onwards, depending on condition. It is also possible to purchase new military binoculars for little money: The Russian BPO are available for about 120 Euro (BPO 7x30) or 140 Euro (BPO 10x42). Of course, these are not without shortcomings, having a strong yellow tint and being somewhat prone to ghost images.

Wisdom No. 3:

Over the decades, the quality of coating was the most influential factor for optical performance

Already during the 1930s, top performance binoculars were engineered for military use. During WWII, some of them were equipped with a single layer anti-reflection coating, which was since then continually improved, leading to better contrast, brightness and color rendition. The introduction of multi-layer coating in the late 1970s has caused another performance boost. Since that time, the color saturation of the image reached that high level we are used to find with modern optics. Binoculars of roof-prism type experienced a final performance jump in the late 1980s when the phase-shift coating was introduced. Since that time (but not before), the best roof prism binoculars approached the contrast offered by high-end Porro prism glasses. This historical development had its implications on the performance of ancient binoculars, regardless of their quality. For example, the Porro binoculars made by Zeiss (Oberkochen) in the 1950s were excellent enough to be even competitive with today's high end binoculars - if they just had a modern coating. With the technology available at that time, however, their colors appeared rather pale when compared to a modern binocular. This is the rule of thumb for anybody who is looking for a second hand binocular with maximum performance: If it is a Porro, it should be made after 1980 (availability of multi layer coating), if it is a roof prism, not earlier than 1990 (phase-shift coating).

Wisdom No. 4:

Optical top performance is already available for 700 Euro - beyond that, binoculars become more compact and versatile.

The top line Porros of Fujinon (e.g. 10x50 FMT-SX), Nikon (e.g. 10x42 SE) or Swarovski (e.g. Habicht 7x42) are good enough to match the optical performance of any other high-end binocular and cost around 700 Euro. But, being of Porro type, they are either heavy and bulky (Fujinon), or, if compact, then restricted to small exit pupils (Nikon SE and EII), or to narrow fields of view (Swarovski Habicht). Then, the Nikon SE is not waterproof, and the Fujinon has got uncomfortable, individually focusing oculars. None of them comes with (luxory) features like twist-up eye-cups or a close focus distance below 3m. In contrast, the high-end roof prism binoculars of Zeiss, Leica, Swarovski and Nikon are offering almost everything at once: Slim and lightweight body, often paired with large exit pupils and reasonable angles of view, are fully waterproof and with central (internal) focuser, but they cost significantly more without being superior (for any practical purpose) in their optical performance.

Wisdom No. 5:

The most versatile binocular is the 8x40

The wide range of specifications found in binoculars is confusing to the unexperienced. Most people tend to select a glass with unnecessary high magnification, e.g. 10x, thereby sacrificing angle of view and stability of image. Others believe a binocular has to provide an exit pupil as wide as possible to be usable under twilight conditions. But those glasses with 7mm exit pupil (7x50, 8x56, 9x63) usually come with an annoyingly small apparent angle of field ('tunnel view') and are, due to large objective diameters, heavy pieces of glass. When used in real life, the eye-pupils then hardly reach those 7mm, and this only for observers in their young ages, so that parts of the collected light are almost always wasted. Finally, there are ultra-light compact glasses, designed for the mobile user. But these come with small prisms and a corresponding small field of view, and their exit pupils (typically 3mm) are narrow so that these binoculars quickly become useless under dim light conditions. The best compromise is a device with around 5mm exit pupil and a magnification which allows to produce a firm and stable image under less than ideal conditions, i.e. not beyond 8x. Therefore, the 8x40 binocular appears to be the best all-around glass. Even as a wide-angle (beyond 60 degs. apparent field of view) and equipped with a proper mechanical ruggedness, these glasses weight no more than 800g, can be taken out on every trip and are reasonably suited for low light applications, too.

Wisdom No. 6:

Tests are helpful to evaluate middle class binoculars - and losing significance toward the low- and the high-end

The idea behind a test report is simple: To pre-inform somebody about strong and weak sides of a binocular he possibly never held in his own hands. Instead, such a review was created by somebody else, including all those potential obstacles like individual experience and personal preferences. This limitation remains of little relevance as long as the binocular is imperfect enough to exhibit a sufficient number of technical faults the reviewer is then able to point on. In this case, each half-way experienced tester should come to about the same conclusions. Things become different once a binocular approaches a state close to perfection, like these 'beyond 1000 Euro cruisers' of Zeiss, Leica, Swarovski or Nikon's top line. It becomes increasingly difficult to discriminate their performance by technical means alone. At this point, individual preferences of the reviewer tend to become the dominating factor for the outcome of the evaluation. My suggestion is therefore: Don't waste your time reading test reports on high-end binoculars, but make sure to get one sample glass and try them out yourself. Technically, any one of them will be good enough, and it is left to your own taste which one is going to be your personal favorite. Another, totally different problem shows up when testing the low-end side: These binoculars are often of mediocre mechanical construction and may display a wide range of de-collimation even at the time of purchase. This is frequently the case with cheaper products made in Russia and China. The test instrument may then not represent the performance level of the series, but just a random selection, and the test result is of limited accuracy and validity.

Wisdom No. 7:

Large objectives deliver more light, not resolution

The power of any hand held binocular is low enough to ensure its theoretical resolution limit being far beyond whatever could be resolved by the human eye. In other words: Binocular observation is never reaching the diffractive limit as defined by the objective diameter. In this regime, resolution solely depends on magnification, not on objective size. A switch from 10x30 to 10x50 has therefore no effect on RESOLUTION at all. However, the light input is increased, and this may, depending on viewing conditions, lead to improved CONTRAST and thereby to images with additional fine details. Quite generally, one may claim the performance of hand held binoculars (of a given power) being contrast-limited, not resolution-limited. Many other factors, including stray light protection, suppression of reflexes by optical surface coating, reduction of residual aberrations and even the choice of the image's overall color tone are of crucial influence on the level of contrast. This is one reason why quality binoculars show actually more within a wider range of light situations than cheaper binoculars (another reason is related to their superior mechanics and, along with that, a higher level of collimation). It is not only size that matters.

Wisdom No. 8:

Medium range binoculars deliver a reasonable performance-to-price ratio

The graphic displays approximate price and relative performance of several 8x30 (8x32) binoculars. It is not to be taken too serious, since obviously there cannot exist any single variable that stands for 'performance'. Still, it helps to demonstrate one fundamental property of the market: Quite generally, performance increases with price, but the gain is slowing down towards the high end sector (the "law of diminishing returns"). Starting with the 50 $ range (there exist cheaper glasses, but see Wisdom No. 1) we are able to find binoculars of already decent quality. For example, the BPC is a somewhat crude, but successful attempt to copy the CZJ Deltrintem. The original is better, but at least twice as expensive, second hand. The medium range starts at about 200 $, where reasonable optical performance is often paired with water resistance and an improved level of ruggedness. Between 200 $ and 600 $, the performance gain is considerable and cannot be repeated, even after adding additional 800 $ for a Zeiss FL. This is the reason why medium range binoculars play an important role in the market. They are driving performance up to a level where differences to the top class become negligible in the majority of viewing situations, while keeping the price on a moderate level.


Wisdom No. 9:

Nowadays, the merits of wide-angle optics are underrated

A Binocular is generally regarded as wide-angle if its apparent field of view is reaching 60 degs (in Japan: 65 degs). Several benefits come along with such a wide angle optics: First, its view is more natural - after all, our eyes are wide angle sensors as well. Then, it is easier to view over large areas without panning, reducing artificial movements of the image. During numerous observations I have further confirmed that a wide angle supports the identification of objects under very low light conditions. Sadly, in recent years, more manufacturers are choosing to shift their production lines towards narrow angled designs, Minox, Pentax or Steiner being just a few examples for this trend. In fact, the creation of good wide angle optics is anything else but easy: Since aberrations are increasing sharply with the angle, sophisticated oculars are required for their compensation, the prisms have to be large, hampering the desire for compact and light weight instruments, and stray light is more likely to enter through wider angles, which requires additional internal baffles and prism shields. But what is much worse: All these efforts remain unnoticed by the public. To the contrary, the 'performance tests' of our consumer's journals are banning the field of view somewhere into the list of specifications, often enough failing to point out its practical importance. Instead, the binocular is punished for 'close-to-edge blur' (ignoring the fact that at wide angles, this edge is far off the center) or its body size/weight. In this way, simple narrow angle constructions are rated higher than their more sophisticated wide angle contenders, a spurious result, but the manufacturers have little choice but to follow this general trend towards simplification to stay competitive. For this reason, I would like to appeal to the consumer to take notice of the benefits of wide angle observation, and to honor the high level of finesse the optical designers have put into quality wide angle optics.

Wisdom No. 10:

The notorious roof vs. Porro debate: In a nutshell

In countless threads, this question is repeatedly raised on Internet discussion boards: Is any one of these prism systems fundamentally superior to the other? The short answer is: No. In fact, today's high end binoculars (when summing up optical performance, mechanical features and price) are currently of roof type - not so much for technical, but rather for marketing reasons: Binoculars carriers like the slim and elegant external of the roof prism body and believe it to represent the 'modern-style' binocular. Since they cost lots of money, manufacturers and dealers can reserve a beefy margin with each sample they hand over to the consumer. The following advantages can be accounted for the roof prism design: With comparable specifications, a roof prism glass is usually somewhat less heavy than a Porro type binocular. This construction also supports an easy implementation of the internal focusing mechanism and hence simplifies the sealing against water. The slim shape leads to a narrow separation of the objectives, so that short close-focus distances are achievable. On the down side, roof prisms require low tolerances during their shaping and collimation, need an additional phase-correction coating, and some of them (except for the Abbe-Koenig type) also a reflective mirror layer. Porro prism binoculars are easier manufactured, require less strict tolerances and lead to shorter light paths through glass material. The latter fact reduces the amount of chromatic aberration which has to be corrected for by objectives and oculars. Their large objective separation leads to an improved stereoscopic view (plastic) over medium-range distances, but prevents close-focus distances below about 3.5m. It is also easier to construct wide angle binoculars using the wide and short body shape of the Porro. In summary, Porro binoculars are cheaper than roof binoculars of same performance level. But with some additional effort and price, modern high end roofs combine top optical performance, compactness and water resistance.

Wisdom No. 11:

Make sure to figure out what you really need - and save money

In recent years I observe a development among the premium range binoculars that somehow resembles that of digital cameras: There is an increasing number of questionable features showing up that are not always required for serious observation work. And obviously not everything that is new and costly is necessarily superior. Do we really need 'flat' transmission curves, i.e. maximum transmission even of the shortest wavelengths, to achieve a fully neutral image tone, and then having to wear sun glasses when observing on bright sunny days? If yes, why not at least adding filter threads to dampen/tune the light whenever necessary? Do we need a super fast and low tension focuser, perhaps at the cost of precision? Do we really want to pay a fortune just to have the circle of maximum image sharpness extended all the way to the edge of field, rather than moving the object of interest a little bit toward the center? Many people are using binoculars in order to observe distant objects. Should these people have to pay extra, or compromise performance, because there are some who would like to watch butterflies at 1.5m distance? And is a binocular incomplete if it is not waterproof? Top binoculars of the 1980s like the Zeiss Dialyt and the Leica Trinovid have not been waterproof either, and did a great job nonetheless. Should not those users who are willing to take good care of their gear have the chance to purchase high-end optics without paying extra for water sealing and shock resistance? Let us hope that the manufacturers will find the right answers to these questions and a proper balance between useful improvements and an overload of features that yield little more than a further increase of costs. But I doubt that this will happen, the race is on, and everybody wants to take the lead with his feature-overloaded and overpriced premium line. The consumer may contribute to stop that price hike, by carefully selecting products that exactly do what he needs them to do, thereby saving his own money, instead of blindly following the trend set by the manufacturers and buying their most expensive gear including their unnecessary bells and whistles.

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