In this review I want to compare three interesting binoculars suitable for use under low light conditions. Such instruments have to be equipped with a large exit pupil diameter, i.e. large objectives at comparably small magnifications. This is an in-house competition between three Zeiss Jena binoculars, produced in three different decades and nowadays available on the second-hand market.
Fig.1: The NVA DF 7x40.
The DF 7x40 was produced during the 60s and 70s for the East German Army NVA (Nationale Volksarmee). It can be regarded as an all-round glass with some low-light capabilities, as to be expected for a border control ('Checkpoint Charlie') binocular. A description of this device was given in another review. The DF can be found in large quantities at e-bay for 200 Euro in good condition.
Fig. 2: The Zeiss Jena Jenoptem 7x50W.
The Jenoptem 7x50W, with more than 7mm exit pupil, is a real night glass. It was probably produced during the 80s. Things are a little confusing because sometimes one can read that the Jenoptem was the successor of the Binoctem, now with multi-coated optics, but there seem to exist Binoctems with multi-coating as well. The smaller 8x30W version was tested here, and the third of the line, the 10x50W, was tested here. The Jenoptem 7x50W appears frequently on e-bay for about 150 Euro in good condition.
Fig. 3: The Nobilem 8x50 B/GA
The Nobilem was the high end line of East German Zeiss binoculars for the civilian market. I am citing the history section of the Docter home-page:
"From the middle of the 70s onwards new developments again became a focus. The binoculars models 8x32 and 10x40 with in-line optics also originated at this time. However, the excellent telescopes NOBILEM 8x50 and 12x50 with first-class performance were only produced for a short time due to the huge efforts needed and the technical demands involved. In the middle of the 80s they were replaced by models of the same name, which were the results of extensive concept studies. This model series has step by step been complemented by further models and variants and has been redesigned over the recent years."
In 1991, after collapse of the GDR, Docter Optic took over the Zeiss binocular production plant in Eisfeld and is since then continuing the Nobilem line. Also, the EDF 7x40, the successor of the DF 7x40, is still in production as a modified civilian version (without IR detector). In the current brochure, however, I can't find the Nobilem 8x50 any more, only a 8x56, 10x50, 15x60 and various 7x50 devices. I still found one 8x50 B/GA in new condition for 360 Euro, including 30 years of warranty. The price tag already indicates that these units are aiming toward the upper class section of the market, although there is still a gap left to the other noble brands. The "B" refers to "Brillentraeger", i.e. with long eye relief and therefore suitable for spectacle wearer, the "GA" means "Gummi Armierung", i.e. rubber armoring.
Fig. 4: The DF 7x40, Nobilem 8x50 B/GA and Jenoptem 7x50W
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)||(kg)|
|Nobilem 8x50 B/GA||7.4||59||19||6.3||1.30|
|NVA DF 7x40||8.5||60||20||5.7||1.30|
Image sharpness: The DF and the Jenoptem display a similar pattern: Very sharp in the center and an increasing softening toward the outer 75-100% of the radius. Star observations are even more selective: The star images remain point-like within the innermost 60% of the radius and almost disappear at the outer edge of the field. It sometimes seems that the Jenoptem is a little sharper in the center, but the DF is keeping a high level of accuracy over a wider field. Very obvious, however, is the fact that the Nobilem performs best here. Stars remain point-like up to 80% of the field and the aberration remains moderate even at the edge. The aberration control of the Nobilem thus shows a visible improvement over the elder generation Zeiss glasses.
Image color: The image of the DF has got a slight yellowish tint. Not on a disturbing level, but noticeable when compared to the other two contenders. The Nobilem appears to be a little yellowish, too, less than the DF but also not completely neutral. In my opinion, the Jenoptem conserves the colors best, but the differences to the Nobilem are subtle.
Rectilinear distortion: All three glasses show a slight pincushion distortion to eliminate the globe effect of the panning binocular.
Stray light: The following situation is a selective test for stray light: You are looking over a clearing to observe the edge of the woods. It is one hour after sunset, the forest is already gloomy but the sky is still quite bright. Its light is entering the objectives and illuminates the inner objective tube walls. A part of this illumination is scattered into the optical path and entering the eyes as a diffuse stray light, reducing the contrast of the image. A glossy finish of the inner tube walls can contribute a lot to enhance this effect, baffling and a well dimensioned prism housing help to suppress the same. Stray light can become an issue under twilight conditions, and that's where night glasses are frequently used, and corresponding care has been taken in the construction of the three contenders. The DF essentially shows no stray light at all. A look at Fig. 4 reveals the obvious explanation for that: The DF practically has no objective tubes; the prism housings begin just behind the objectives and are wide enough to prevent scattered light invading the optical paths. The objective tubes of the Jenoptem and Nobilem are well baffled and stray light, although visible, remains on a moderate level. It is a bit surprising to find that the Jenoptem actually performs better than the Nobilem. In fact, Fig. 4 also shows that the Nobilem has long tubes and short prisms, whereas the Jenoptem has shorter tubes and longer prisms. One may speculate whether this makes the Jenoptem less prone to stray light.
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 Jenoptem is clearly displaying a line of multiple, well localized and fairly bright reflections if a bright light source is positioned close to the center of the field. When shifting the light toward the edge, the reflections disappear. In the Nobilem, only a single diffuse spot appears, but another, diffuse and dim glare appears when the light is shifted outside the field - perhaps the effect of stray light (see above). The DF shows no ghost images in the left tube, but in the right eye, a fairly bright reflection takes place at the reticle, and this one has more intensity than the Nobilem's. However, the effect disappears soon when the object is shifted toward the edge of field. To judge which one of the glasses shows a more disturbing ghosting is not easy. I would give it an even match between the Nobilem and the DF, and a lower performance of the Jenoptem. But one should note that the DF, with reticle removed, would definitely beat the Nobilem.
Low light performance: It has to be quite dark before differences become obvious. Then, however, it is all the more impressive how the Jenoptem and Nobilem outperform the DF. Their images just remain brighter and show a lot of more details than the NVA glass. Perhaps this is just in parts a consequence of their larger exit pupils: According to the DF's manual, its transmission is 75% through the left tube and 68% through the right tube, and this is not much for today's standards, where transmission rates close to 90% are reached with the help of optimized surface coatings. The DF is still singly coated, the Jenoptem has got a multi-layer coating as well as the Nobilem. After lengthy hours of observation, I was unable to find any difference in the low light performance between the Jenoptem and the Nobilem. This could be related to the fact that at my age (around 35), my eye's pupils won't open up to 7mm any more, so I can't make full use of the light offered by the Jenoptem. If the observer's pupils have 6mm, then the 7x50 Jenoptem is stopped down to 7x42 only. Also, the Docter's brochure explains that the individual prisms of the Nobilem are cemented to reduce the air-to-glass transitions, and this should also contribute to a higher transmission rate and to the good night performance of this binocular.
|Nobilem 8x50 B/GA||2.5||3||1||2.5||2.5||2||2||15.5|
|NVA DF 7x40||2.5||1.5||3||2.5||1||1||3||14.5|
Again, a warning regarding the 'final score' is adequate here: The higher number in the final score does not necessarily mean that a binocular is better, because this is just the numerical sum of scores it received for the various features. It is always required to figure out which of the features are of high relevance for the user and which are not, and this depends on the intended spectrum of application.
The Jenoptem cannot quite match up with the other two contenders. But a closer look reveals that its deficiencies are essentially rooted in constructional aspects like mechanical ruggedness and angle of view. If these are of little relevance, the first and the last column of the table may be skipped and suddenly the Jenoptem is as good as the DF or Nobilem. When it comes to image quality, the Jenoptem is competitive with the more costly devices, but at a reduced field of view.
As it was to be expected, the DF and the Nobilem had a tough competition. With the reticle removed, the DF would take away another point from the Nobilem because then the ghosting in the right eyepiece were diminished. The question then arises whether the Nobilem is actually worth the extra money. The answer is: Yes, if low light performance has got a high priority. Here the DF definitely cannot match. The specification of the Nobilem, 8x50, also suggests it to be used as a general all-round glass. As such, however, the DF is also competitive, costs half the price and has got a margin in terms of water-resistance and ruggedness. One may speculate whether this could be the reason why Docter has discontinued the 8x50 model. With more and more DFs showing up on the surplus market in recent years, the 8x50 had got too much of competition - ironically from devices of the same factory! The construction of the DF, with a short and stubby body, seems to have one advantage when it comes to stray light suppression. It is interesting to note that the early Nobilem-S models of 1980 were built with a similarly shaped body. The later reconstruction of the Nobilem series then led to the present appearance with smaller prism housings and longer objective tubes. I can only speculate whether the short form employed objectives with shorter focal length which caused a nightmare to keep them free of chromatic aberration. At least in the DF, or its civilian version, the Septarem 7x40, this construction principle was realized, and successfully so.
Fan's Binocular Collection
An interesting article (in German language) about the construction of the Octarem 8x50 (which is almost identical to the Nobilem), published in 1985 in the Jenaer Rundschau. Thanks to Sebastian Rabus for scanning this document!
Last updated: 2003