Review: Military 7x40 binoculars

Binoculars, designed for military applications, are often found to be of 7x40 type. This specification was very common within the East-Block states, but not exclusively so. The Avimo was a British design, and a couple of Arabic and South Asian countries were supplied with East German or Soviet equipment and used the same optics as well. It is said that recently US soldiers, fighting in Iraq, were eager to capture NVA DF binoculars which were still abundant among Iraqi's troops.

Why did 7x40 turn out to be so useful for military applications? Because it provides a reasonable compromise between power, low light performance and weight. In contrast to 8x30 binoculars, being another popular choice for armed forces, the 7x40 remains usable under low light conditions, and it is much more likely to find a bunch of troops moving around in the night than under bright sun. At the same time, the 7x40 is more compact and mobile than 7x50, the latter being a favorite choice for naval applications. Modern troops, however, are nowadays equipped with electronically amplified viewing devices and do not any more rely on binoculars with large exit pupils.

The present review compares a selection of five 7x40 military binoculars, along with a modern civilian glass, the 7x42 Habicht of Swarovski.

The Carl Zeiss Jena DF 7x40, old version with hard-rubber eyecups (1964)

The 7x40 DF (Doppel-Fernrohr) of the NVA (Nationale Volksarmee) was introduced in the 1960s and was the first binocular built by Carl Zeiss Jena from scratch since the days of WWII. It replaced the 7x50 Binoctar, 10x50 Dekaris and 8x30 Deltrentis, individual focus versions of Jena's earlier classical line of binoculars. The 7x40 DF was given a short ('stubby') body shape, thereby keeping it rather compact, despite of its large prisms and considerably high weight. With its thick rubber armor, its large oculars with long eye-relief (suitable for use with gas-mask) and the eye catching window of its infrared detector re-charger, the DF had become the classical example of a full fledged military binocular, the blueprint of later 7x40 clones which adopted the same design philosophy. In 1980, it was replaced with the 7x40 EDF, a roof-prism construction which was more compact, but with smaller field of view. The serial number of 3390911 indicates a production in 1964.

The IOR-SA 7x40, version of 2001

Quality binoculars for the Romanian army are produced by IOR-Bucuresti, founded in 1936 and from 1937 to 1945 part of the war-industrial complex of the occupying Germany. IOR stands for 'Industry Optic Romania'. The IOR-SA 7x40 was constructed in collaboration with Carl Zeiss Jena, which explains its obvious similarity with the DF 7x40. In contrast to the DF, it is still in production, comes with modern multi-coated lenses, and is nitrogen filled. The contoured eye-cups are useful to prevent stray light entering from behind or the side. A detailed review of this binocular was written by Scott Powers. The serial no. of 0317-01 indicates a production in 2001.

The PZO 7x45, year of production: unknown

With 45mm objectives, the PZO occupies a position between the 7x40 and the night-specialist 7x50. It was produced for the Polish army by PZO (Polskie Zaklady Optyczne), a factory located close to Warsaw. After the end of the cold war, the 7x45 remained in production and is nowadays called 'LP-7x45Z'. Like the IOR-SA and the NVA DF, it is featuring an infrared detector, a robust rubber armor, snap-in objective covers and a long eye-relief. The eye-cups are contoured to shield the eyes from side stray light. This sample seems to be without serial no., and it is not easy to estimate its age. The lenses appear to be multi-coated, although not with state of the art technology.

The GG95 7x40, year of production: Late 1990s

This Chinese 7x40 binocular is produced in Nanjing and represents the military issued version of the Hioptic MBHA0740r. I was unable to figure out whether both versions do actually differ in any specifications, but I suspect the military sample to have a somewhat improved coating. The optical design is featuring an air-spaced doublet objective (tele-objective type) and an ocular construction using five lens elements in three groups. According to the manual, this binocular is immersible in 1.5m deep water for one hour and operational within -43 to +55 degs. centigrade. In contrast to most other military binoculars, it has got no rubber armor. The imprint on the left prism housing reads 'Y/GG95-7' and I shall refer to it as 'GG95'.

The Avimo 7x42, year of production: 1980

This 7x42 binocular was made by Avimo Optical Imaging (now: Thales Optics) in UK during the 1980s. It was later licensed to Rollei Germany, and nowadays Russian copies made by BELOMO in St. Petersburg have been spotted on Internet auction sites. This binocular has got a characteristic body shape. It is reported (in Seeger's book about military optics) that these devices were not popular with the British troops in combat conditions during the Falklands war, because of their curious 'cranked' tubes. This meant that the observer had to move his head up a few inches higher than with conventional constructions. This binocular is of fixed-focus type and has to be used with eye-glasses by anybody with visual defects. Its eye-relief is long enough, however, and the telescopic eye-cups are effectively shielding any side-stray light. The present sample was made in 1980.

The Swarovski Habicht 7x42, current production

The 7x42 Habicht is made by the Austrian manufacturer Swarovski and the only civilian binocular of this test. It can be regarded as a modern high-end Porro of classical design, but made with state of the art materials, lens coating and sealing techniques. Despite of its central focuser, it is fully waterproof and nitrogen filled, and there also exists a rubberized ('GA') version. I was informed that a couple of 7x42 GA binoculars are in service at the Austrian army, so this is actually not a fully civilian glass. Compared to its competitors, it is amazingly light and mobile, but the eye-relief of 14mm may be a little short for comfortable use with eye-glasses. In Germany, this binocular costs about 600 Euro (the 'GA' version: 700 Euro).

In front: NVA DF, GG95, IOR-SA, three models with plenty of similarities. Behind: PZO, Avimo, Habicht

The following table is summarizing the specifications of the contenders.

Optical performance

Image sharpness: At the center, all of the six contenders have got an excellent resolution. But they differ as soon as the edge of the field is approached. Here, the Swarovski performs best, where the star test displays point-like images beyond 80% (radial) off center. Even at the edge, the deformations of the stars remain low. The PZO is next with about 75% of point-like stars and moderate blur at the edge, closely followed by the GG95 (little less than 70%). Both NVA and IOR display star images that start to deform a little less than 60% off center. At the edge, the deformations are high. So far, the edge sharpness of the contenders is quite accurately correlated with their angle of field: The smaller the angle, the better their edge resolution. This indicates that they are all using oculars of comparable performance. However, the Avimo is an exception: The stars are fine at the center, but already less than 50% off they start deforming. This poor performance is of course a consequence of its fix-focus feature. It is not possible for me to find the optimized focus for my eyes, so that the full performance of this binocular remains inaccessible.

Image color: The differences are small but visible in a straight comparison. The only binocular which seems to have a fully neutral color tone is the Habicht. The Avimo has got a very slight yellowish tone, and so are, a little stronger, the GG95 and the NVA DF. The IOR-SA is already visibly yellowish, although much less than most of the Russian binoculars or the NVA EDF roof-prism binocular. The PZO has got a slight yellow-brownish image tone, of similar intensity as the IOR.

Rectilinear distortion: All binoculars show a slight pincushion distortion, which is intentionally installed to eliminate the globe effect and in this way to provide a smooth panning.

Stray light: Under difficult viewing conditions, especially at twilight, light from sources outside the field can enter the objective lenses through a large angle to illuminate the tube walls and is, partially, scattered into the optical path. It then becomes visible as a diffuse fog, most intense around the edges of the image, reducing the contrast. Only the GG95 and the Avimo are displaying some problems here. At the prism entrance, the GG95 has got a shiny metallic ring which may be the cause of the stray light. Inside the Avimo, it seems that a glossy finish of the internal tube is responsible for reflections. In both cases, a minor modification would improve the performance of these binoculars a lot. For military applications, an excellent stray light protection is required to ensure the maximum contrast under difficult light conditions. The other four contenders perform very well in this discipline and there is nothing left to complain about.

Left: A shiny metallic ring in front of the prism entrance, the cause of stray light inside the GG95?

Right: A glossy finish inside the Avimo's internal tubes

Ghost images: If, at night, a bright object (street lantern, moon) is positioned into the field, reflections on the air-to-glass surfaces take place, which can lead to multiple 'ghost' images of the light source. The Swarovski is perfectly preventing any ghosts, even when tested against high intensity lanterns. This indicates a top quality coating. In fact, an image as clean as that is hard to find among most top level binoculars, since these are usually of roof prism type and are producing a more or less intense spike - a diffraction effect at the roof-edge. Military glasses have got a reticle inside one of their oculars, and this glass plate usually serves as an extra source of reflections. The GG95 and the Avimo seem to use reticles which are properly coated, displaying a high resistance against ghost images. I suspect that the GG95 performs better here than the MBHA0740r which I had tested earlier. In contrast, the PZO and the NVA DF develop a ghost image of higher intensity at their reticles. Although the IOR is slightly better at this side, I found a rather bright ghost image inside the left tube, which has got no reticle. Anything similar was not visible when I tested another sample of the IOR, and I suspect here we may have an example of quality control failure. Perhaps, one lens surface remained uncoated, or has got a defective coating, and considering that a blank glass surface reflects 4% of the incident light, compared to 0.2% of a typical multi-coated surface, such an uncoated surface might be able to spoil the ghost-resistance of the entire light train.

Low light performance: This is a difficult test, since we have got six binoculars of almost identical specifications and the differences in low light performance are naturally very subtle. Still, I believe to have found the Habicht and the Avimo producing the brightest image under very low light conditions (at night, with clear skies and the half-moon near the zenith). With short distance, the GG95, IOR and PZO were following. Once more I found the performance of the PZO in this discipline a little disappointing: On paper, this binocular with its large exit pupils should actually perform best, but it reproducibly remained behind the Habicht and Avimo. This indicates that its light transmission may be comparably poor. It is no surprise to find the NVA DF at the end of this competition. It is only single-coated, and its light transmission is specified as 75% (without reticle), whereas a modern binocular like the Swarovski Habicht can pass between 90% and 95% of the incident light. It should also be noted that, in case the low light is paired with isolated light sources, the Avimo and the GG95 would lose performance because of their response to stray light.

Mechanical construction

Summary

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

Without any doubt, the Swarovski Habicht delivers the best optical performance of this competition. This is a high tech Porro prism binocular with almost perfect optics and accurate mechanics. It has got a single weakness only, which is its flimsy field of view. This is a matter of design philosophy: Stopping down the field of view brings along an entire bunch of advantages. The edge sharpness improves, because the edge is shifted towards the center, and aberrations are growing nonlinear with the angle of field, so that most problems are avoided once this angle is kept small. It is also easier to protect the binocular against stray light if the incident angle is stopped down. Then, smaller prisms are required, keeping the instrument slim and light. Finally, oculars with narrow apparent fields of view can be of simpler construction than wide angle binoculars (e.g. 3 lens element reverse Kellner instead of 5 lens element Erfle), are therefore cheaper, provide a better light transmission and are less prone to ghost images, because they contain less air-to-glass surfaces. However: I believe that the wide angle experience adds to the joy of using binoculars, and an apparent field of view of only 45 degs. is just too little for my taste.

Behind the Swarovski Habicht, with 31 points, there is a considerable gap, and all five competitors are then bunched between 24 and 22 points. It is fair to claim all of them playing in the same league and I would not suggest to declare any one as the winner. The accuracy of such a field test is not high enough to seriously claim the IOR or DF, with 24 points, being better than the Avimo with 22 points. Still, this test has revealed a couple of interesting common features and also differences.

There are the DF and its clones. The old NVA glass is still competitive and does not need to hide behind younger designs, but its coating is naturally far from being state of the art. It is a very heavy device, too, and here the competitors have become more user friendly over the years. The IOR-SA is essentially a DF with somewhat reduced prism-size. As a consequence, it has got some vignetting close to the edge of the field, but a comparison using the above Table shows that both binoculars perform almost the same. I don't know the reason why the IOR has got a somewhat more pronounced yellow tint, whether this is intentionally so (choice of radiation resistant glasses) or simply the result of poor glass quality. Its coating is altogether better than the DF's, because it was made almost 40 years later, but there may be a problem with quality control (see the ghost image section above). The GG95 is perhaps another variant of this construction. It is similar to the IOR, but without rubber armor and with somewhat reduced field, thereby avoiding vignetting and improving the edge resolution. Also, its weight is further reduced, and I would attest the GG95 a much improved mobility compared to the DF, which is almost one pound heavier. The GG95 also displays quite a high quality lens coating, but a weak point is its response to stray light, which may be avoidable without causing much of extra production costs.

With 45mm lenses, the PZO has got the largest objectives of the competition, but it is unable to take advantage of that fact. Its low light performance is on average level only, which obviously is the result of poor light transmission. On the positive side, its stray light protection is excellent and so is the resolution close to the edge of the field. I would like to know whether the current version, the LP-7x45Z, comes with improved coating and transmission, which would significantly enhance the performance of this otherwise fine binocular.

The Avimo is especially interesting. It has got a quality coating, excellent low light performance, and high resistance against ghosting. Unfortunately, this impression is spoiled by a glossy finish of the inner tube walls, causing a stray light which could easily be avoided. Confronted with examples like that, I sometimes ask myself whether such an obvious defect could be left unnoticed during those field tests which are mandatory for defense projects. Apart from that, I dislike the fixed-focus feature of this binocular. I believe that every optical instrument has to be focused in order to deliver maximum performance. The argument, such a binocular should be used with glasses only, is of little impact. How many people are wearing glasses which are perfectly tuned to 100% compensate their visual defects? I have often enough experienced that my eyes perform somewhat differently from day to day, and I always turn the focus wheel to find the optimum position during my observations. I don't want to miss this opportunity to get the best out of the instrument I am using.

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