Review: Current Chinese 8x40 binoculars

by Holger Merlitz

Recently, United Optics (UO) have announced the introduction of the new BW8 roof prism series and also added a new model, the 8x40, to their BW5 series. Since I have got another China made 8x45 by LOAVA, which is also available at United Optics as part of the BW7 series, a performance test of these 8x40 binoculars currently made in Kunming appears interesting. This review will also offer the opportunity to evaluate the overall performance level reached by Chinese binoculars, when compared with the competition found elsewhere on the planet. Do Chinese binoculars have by now reached a level which could threaten the upper middle class of binoculars made in Japan or Europe? If not, how far apart are they right now, in terms of performance and built quality, and what has to be done for their improvement? These questions shall be addressed in the conclusion of this report.

Fig. 1: The United Optics BW8 (non-ED version)

The BW8 is a series of modern style roof prism binoculars, of compact shape and low weight. There are other models available, 8x32, 10x42, 10x48 and 12x48. They can be ordered with ED glass objectives which are supposed to reduce chromatic aberration (the sample in this test is a non-ED version). Additional optional features are dielectric mirrors for the prisms (which are superior to the metallic layers in terms of reflectivity and color fidelity) and the phase correction coating (P-layer) for superior contrast and resolution (the sample in this test has got both of the optional features). Interesting is the diopter-lock option: The ring for the diopter setting can be locked when pushing it down, and unlocked when pulling it up. In this way, any unintentional operation of the diopter ring is prevented. The objective covers are attached to the central hinge through strings to avoid them being lost in action. The twist up eye-cups can lock in 4 different positions so that a convenient eye-relief may be selected and secured.

Fig. 2: The United Optics BW5. Right: Undersized objective lens, stray light shielded prism entrance

The BW5 is a bulky and robust Porro prism design for serious professional applications. This series does also contain a 7x50 and 10x50, and individually focusing versions (for military or marine use) are available as part of the otherwise identical BM3 series. The 8x40 looks like the 10x50, the objective tubes of which have been cut short. The 40mm lens is quite a bit smaller than the objective tube diameter, which could easily host lenses of 45mm diameter. Considering the high weight of this device (almost 1 kg), the body appears oversized for a 40mm binocular, but this leaves a lot of excess space for stray light protection as will be discussed later. This binocular appears very solidly built, but the body is quite wide and the focuser cannot be operated comfortably with small hands. Like the BW8, it has got objective covers attached to the body and twist up eye-cups. The latter do not lock, but they are turning stiffly enough so that an unintentional operation is unlikely.

Fig. 3: The LOAVA 8x45 (United Optics BW7)

The LOAVA 8x45 has been presented in a previous report on this web-site. It is a member of the United Optics BW7 line which also contains 7x50, 10x50, 12x50 and 16x50 models. Compared with the BW3, this binocular is rather compact and mobile, though it appears less robust and has got some issues with its focusing unit (to be discussed later). The technical specifications for this binocular are incorrect: Its field of view is not 8.0 degs. as specified, but, according to my own measurement, 7.6 degs., and the exit pupil is not 5.6mm, but roughly 5.0mm. The latter number implies that there must exist a serious vignetting of the light cone which effectively turns this binocular into a 8x40. I have observed a similar reduction of the exit pupil with the BW7 10x50 as well. The twist up eye-caps can lock at any height which makes them very comfortable to use.

Fig. 4: The LOAVA (BW7), BW5 and BW8.

The following table summarizes some of the specifications of the contenders.

  Real angle Apparent angle Eye relief Exit pupil Weight
  of view (deg) of view (deg) (mm) diam. (mm) (gram)
United Optics BW8 8x42 7.0 56 17 5.2 760
United Optics BW5 8x40 8.0 64 18.3 5.0 980
LOAVA (UO BW7) 8x45 7.6(a) 60 19 5.0(b) 890
a: Specified: 8.0 degs.
b: This makes it an effective 8x40

Optical performance

Angle of view: The BW3 is widest with 8.0 degs., followed by the BW7 with 7.6 degs. and the BW8 with 7.0 degs. In this sense, the BW3 is the only true wide angle binocular among the three candidates. Its specified field of view appears correct, like the BW8's, and unlike the BW7's (which was officially specified as being of 8.0 degs.).

Image sharpness: Is perfect within the central region of the image. About 70% towards the edge, the BW5 displays the first traces of image blur, and the same happens with the BW8 and BW7 at roughly 80%. When comparing these results with those of other binoculars of similarly wide apparent fields, obviously all three of them perform rather well. This implies that the optical design of these binoculars is well done, even the top line binoculars of Zeiss and Leica display a similar amount of image blur in their outer fields.

Image color: Is fine with all three candidates. The BW8 displays a slightly warmer color tone, but not intense enough to be denounced as a "yellow tint". Both of the Porro binoculars display a little bit colder image color. All three can be regarded as being neutral in their color rendition, it is rather a matter of taste whether the user prefers a warmer (slightly yellowish) or colder (slightly bluish) image tone.

Rectilinear distortion: All three contenders display a small amount of pincushion distortion, which is implemented intentionally to compensate for the globe effect while panning. This distortion appears to be slightly less in case of the BW5, but differences are small and I was unable to detect any visible globe effect with the BW5.

Stray light: In this respect, the BW5 displays an excellent performance. Even under difficult light conditions, after sun set or during the night and near bright objects, this binocular offers a high level of stray light resistance. The reason is first of all the oversized construction of its body: There is plenty of space inside the optical tubes where the stray light can be diffused without entering the optical train. Also, the prism entrance appears to be shielded with a hood which is properly painted using a black, non-glossy finish. To the contrast, I can see glossy metallic structures inside the tubes of the BW7, which is therefore more sensitive to stray light. The BW8 does also display a moderate amount of stray light under difficult light conditions, the origin of which is not clearly discernible. Something appears glossy just at the prism entrance, but I am not sure whether or not this might be the origin of the observed stray light. It is surely more difficult to properly shield a binocular as slim as the BW8, which has got little space left for effective baffles and prism shields. It is also important to treat the edges of each of the lenses with non-glossy black paint in order to reduce stray light generation inside the lens.

Ghost images: The ghosts are produced when light of a bright source is reflected at one of the air-to-glass surfaces and, after a second reflection, scattered back into the light path. A high quality anti-reflection coating helps to diminish these ghosting effects. When checking with the moon or a usual street lantern in the night, the BW7 is generating the least number and intensity of ghost images, whereas the BW5 displays a few additional reflexes. This may indicate differences of the quality of the anti-reflection coating, but there exist additional factors which affect the generation of ghosts, such like the ocular design. i.e. the number of lenses and the curvature of their surfaces. The BW8 displays a low intensity of ghosting, similar to the BW7, but there is another issue: The generation of spikes at the roof-edge. A point-like source (distant street lantern, or bright planet like Venus) is generating a straight line of light ("spike"), which is oriented perpendicular to the roof edge, and since there are two roof edges (one in each tube) with different orientations, the two spikes form a cross-like structure. These spikes are the result of light diffraction at the roof edges, and their intensity indicates the precision with which the roof edge has been polished. With high end roof binoculars, these spikes are almost invisible, but the BW8 is far away from that level of perfection.

Low light performance: On paper, the BW7 should win here, because it has got the largest objective lenses of 45mm. But due to internal vignetting, this binocular is effectively a 8x40 and has therefore no more light to offer than the BW5. There is still a slight advantage with the BW8 which has got 2mm additional lens size. However, I was unable to detect any significant difference between these binoculars with respect to their low light performance. With roughly 5mm of exit pupils, they are well equipped for observations after sun set or inside a gloomy forest under cloudy skies. In some situations, the BW5 delivered the most convincing performance, but this was due to its superior stray light resistance rather than a result of any superior light transmission.

Mechanical construction

The overall best built binocular among the three candidates is the BW8. First of all, it is the only one which I would believe to be fully waterproof and also immersible. The both Porro binoculars are surely splash-waterproof, but considering their focuser being of the external type (also not very precise ones) I would rather select the individual focusing BM3 military version of the BW5 if I had to use it on a boat. The BW5 has got a very rugged construction, but its focuser has got a mechanical play which makes a precise focusing somewhat difficult. As an additional issue, the infinity setting of this focuser coincides with the extremal setting of the focusing wheel, so that short-sighted people would be unable to focus this binocular without their glasses. The focuser of the BW7 is even more fragile: Apart from a mechanical play, the ocular bridge is tilting during the process of focusing, so that the both eyes do not stay in focus and the diopter setting has to be turned to get them back. This is quite annoying and significantly slowing down the operation of this binocular. The BW8 has got no such issues, its internal focuser is working precisely and without any play. All three binoculars are suitable for eye-glass wearer, and their twist up eye-cups allow for a comfortable setting of the eye-relief.


The following table is a summary of the above observations. The best performing binocular gets three points, the following contenders two and one, respectively. In the case several contenders occupy identical ranks, the scores are averaged.

  Angle of Image Stray Ghost Low Image Mechanical Final
  field sharpness light image light color construction score
United Optics BW8 8x42 1 2.5 1.5 1.5 2 2 3 13.5
United Optics BW5 8x40 3 1 3 1.5 2 2 2 14.5
LOAVA (UO BW7) 8x45 2 2.5 1.5 3 2 2 1 14

The 'final score' is the sum of the individual scores and is intended to serve as an orientation only.

These binoculars are playing in the same league, each of them having certain advantages and disadvantages. When considering the optical performance, the BW5 has got a slight advantage. This is mostly due to its wide field of view and excellent stray light protection. Its coating can probably be improved a little bit to make it even with the BW7 (LOAVA). But the BW5 is also very bulky and heavy for a 8x40. I wonder why the engineers in Kunming did not put 45mm lenses into this instrument, there would be enough space available and the prisms appear properly dimensioned for the larger light cone. For sure its central focuser has to be improved, but this is an even more urgent issue with the BW7, which would also need more attention regarding its stray light performance. Apart from that, the BW7 is a very mobile and versatile binocular of decent performance. Even more compact is the BW8, and among the three candidates, it is the one which is most pleasantly handled and operated. Apart from its lower weight, the handling does benefit from its accurate focuser which allows for a quick and precise setting. This binocular would require prisms of higher quality, however, in order to improve its performance significantly. Also, similar to the BW7, its stray light resistance should be improved.

How far have binoculars "Made in China" come during the past 5 years? In my opinion, the review on this page has confirmed that by now there exist several lines of binoculars which offer a decent performance level. The quality of coating has been continuously improved over the years. It is also obvious that the optical designers know how to operate their software in order to generate binoculars which are well corrected over reasonably wide field of views. Five years ago, decent binoculars from China were still rare items, and to find a good one was similar to winning a lottery. Today, it is easy to find binoculars of considerable performance and reliable quality for a reasonable price, and this is the case for many different sizes, including giant binoculars for astronomy.

Nevertheless, I still do not see any binocular made in China which would be able to challenge the upper middle class of binoculars made in Europe or Japan. The reason for that can be traced down to the patchy performance pattern of each binocular presented in this test: Each binocular performs well in certain aspects, but has also got serious flaws in other aspects.

There are two ways the Chinese optical industry might want to go: The first one would be to continue as before, and generate products which are not perfect, but decent enough for the majority of users and of low price. They have optimized that route by now and are probably able to make a reasonable profit with that approach. Problem is: With increasing competition on the market, the margins are going to drop and in the long run there may be other countries arising which will be able to learn how to produce for even less money.

It may therefore be wise for the Chinese optical industry to increase the quality level of their products towards the upper middle- and even premium class, a path which had been chosen by Japan about 30 years ago. In order to achieve this goal, however, it would require commitment, and attention to every detail. In the premium class, a binocular with dozens of perfect features and just a single flaw is still regarded bad. To step up the quality ladder, the entire production chain has to be optimized. Prototypes have to be built which are then tested in the field, under realistic conditions, and gradually optimized. This is necessary because no optical design software is able to evaluate the stray light and mechanical properties of such an instrument in a reliable manner. It requires a close partnership between optical designer and testing personal, so that both of them are able to accumulate experience and work hand in hand to optimize the product. Additionally, the quality control inside the factory has to be improved. This is beneficial not only to reduce the tolerances during the manufacturing process, but also delivering a valuable indicator for the still existing problems of the product, which are then immediately being corrected.

Remark (September 2009): Meanwhile, I have tested the new Zen-Ray 7x36 ED2, which shows some improvements over the bunch of binoculars presented here.


The information given in this report reflects the personal impression and opinion of the author only. I cannot guarantee for the accuracy of any given specification. I have neither been payed nor have I been supported in any other way to write this review. I thank United Optics for the BW8 and BW5 test samples and LOAVA for the 8x45 sample.

Holger Merlitz:

Back Home

Last updated: March 2009