Review: Fujinon 10x50 FMTR-SX vs Sky Rover 10x50 Banner Cloud

Already at the time of its introduction in 2003, the Fujinon 10x50 FMTR-SX gained the reputation of being a perfect handheld binocular for astronomy. With its wide field of 6.5°, eyepieces with field flattening lenses and superior edge-sharpness, in combination with effective lens coatings for high-contrast images on bright objects, the FMTR-SX was then without serious competition. Meanwhile, some of the high-end manufacturers have introduced binoculars with wider fields and superior edge-sharpness, but at a multiple of the Fujinon's price. With the Sky Rover Banner Cloud (SRBC) series, binoculars with outstanding optical performance have recently been made available with price tags below the Fujinon's. In the present report I am going to compare the SRBC 10x50 with the Fujinon 10x50 FMTR-SX. We will evaluate where the Fujinon stands now, more than 20 years after its introduction, and whether in 2024 it is technically possible to construct binoculars that are both superior and cheaper than the Fujinon.

Fig. 1: The Fujinon 10x50 FMTR-SX, serial no. 60A2A03829. The rubber eyecups are shown in their downfolded position.

Fujinon's FMTR-SX series consists of very well built binoculars with massive prism clusters and eyepieces. These eyepieces have an extra long long eye-relief and are focused separately, as it is commonly found with military binoculars. The 'F' in FMTR stands for field flattening lenses as part of the eyepieces to reduce field curvature, improving the edge sharpness, and 'R' stands for the rubber armoring. There have been FMT-SX models around which came without the rubber layer, but as of 2024 they seem to be discontinued. 'MT' stands for marine tested which specifies the device being water- and shockproof according to military standards, and 'SX' denotes the coating technology, based on a sophisticated electron-beam depletion method that yields a precise control over the thickness of each of the several dielectric layers. This 10x50 is a rather recent purchase and I expect it to be state of the art in terms of coating technology, which probably has been updated during the last two decades of product evolution. Currently it comes with at a modest price tag between 800 and 900 Euro, as compared to 700 Euro in 2003.

Fig. 2: The SRBC 10x50, serial no. 36627160

The Sky Rover Banner Cloud (SRBC) series has been around since 2023, with the 10x50 variant arriving in 2024. These binoculars have instantly gained considerable attention among the binocular communities due to their exceptionally wide and flat fields, which resemble the specifications found in the very high-end sector of the binocular market, but at a fraction of the price. Discussions are ongoing about how far the various SRBC models manage to reach high-end performance and where they are lacking, but there is now doubt about the fact that the introduction of these binoculars has sent considerable shockwaves through the binocular market. Earlier this year I had reviewed the 12x50 SRBC, and meanwhile I have purchased the new 10x50, which I have tested over a period of two months. It is currently available for 600 US$.

Fig. 3: Fujinon 10x50 FMTR-SX and SRBC 10x50

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

Optical performance

Image sharpness: Both binoculars offer a perfect sharpness over almost the entire field of view. My comparison, carried out on stars of the 2nd magnitude brightness range, indicates that the SRBC is practically sharp to the edge. With a bit of care it is possible to determine a narrow ring-like section between 80% and 90% off-center in which the SRBC's image turns a little softer by a slight amount. This so called 'Absam ring' (named after the Swarovski 8.5x42 ELSV in which this phenomenon has been first reported about 2010) is easier visible when slowly panning over a fine-structured surface, but almost impossible to notice under the night sky. Between 90% and the field-edge, the SRBC is again perfectly sharp. With the Fujinon, the innermost 80-85% are sharp, surrounded by a periphery which gradually turns blurred toward the edge. I was slightly shocked to notice how far out of focus the stars seemed to be right at the edge, and these observations seem to contradict an earlier report of 2003 according to which the Fujinon seemed to perform better. Please check the discussion about binocular performance and observer's age at the end of this report. The SRBC wins this point.

Image color: Both binoculars offer a perfectly neutral image without any visible color tint. In terms of brightness (during daytime) I see no difference as well. Note that the Fujinon used here was probably of recent production and it may profit from state of the art coating technology, so that its transmission (which is not specified by Fujinon) is possibly somewhat superior to older samples of 20 years ago. The SRBC is specified as having 90% transmission and it appears equally bright. This point is split.

Rectilinear distortion: Both binoculars display a slight amount of pincushion distortion which helps to reduce the globe effect of the panning binocular. I cannot distinguish any significant difference in terms of distortion, although, while panning, the SRBC seems to exhibit a little bit of a globe effect which I don't see with the Fujinon. This difference may be due to the wider angle of the SRBC, which yields a more immersive image and thus may be rather sensitive to trigger an anomalous panning behavior. As it has been traditionally handled in my earlier reports, this discipline is not part of the scoring, since the effects of distortion on human perception are of highly subjective nature.

Stray light: During daytime, none of the contenders shows any significant glare. When the ambient light level goes down, the eye pupils expand, and here the Fujinon can show some arc-like areas of whiteout in the peripheral areas of the field. This occurs during the advanced states of twilight after sunset, e.g. when observing into Western direction in which the sky is still illuminated. Here, the SRBC displays a superior resilience against glare.

Fig. 4: The exit pupils of the Fujinon (left) and the SRBC (center). The Fujinon exhibits a prism leak just outside the exit pupil (lower left) which generates glare when in contact with the eye pupil. The SRBC shows two bright structures, which arise while reflecting backlight on screws, but they are harmless because invisible during observation. Right: Rainbow spikes, seen through the SRBC on a triple of bright spotlights (see discussion in the paragraph below about ghost images). The horizontal spike is the usual diffraction on the roof edge.

Comparing with my old notes, I found the Fujinon to perform worse in terms of stray light 20 years ago, whereas presently it appears quite OK, despite of the fact that the prism leak is still present and unchanged. Again, I refer to the discussion at the end of this report for an explanation. The SRBC is not entirely free of stray light and it can exhibit a loss of contrast when during the night a light source is placed in certain directions just outside the field. Fujinon behaves similarly in these setups. Altogether, I give the SRBC the edge here and thus it receives the point.

Ghost images: If, at night, a bright object (street lantern, moon) is positioned into the field, reflections on the air-to-glass surfaces can take place, which can lead to multiple 'ghost' images of the light source. This does not happen with any one of the contenders, indicating highly efficient anti-reflective coatings. With really bright lights, the SRBC exhibits spikes as a result of diffraction on the roof-prism edge. Here the Porro prism rules and the Fujinon shows a perfectly clean image of even the brightest objects. The SRBC can under certain conditions generate another, unusual kind of spike, which displays rainbow colors and is thus known as the 'rainbow-spike' (right panel of Fig. 4). I haven't noticed this phenomenon, which is frequently discussed on the Internet discussion boards, with the SRBC 12x50, which I had reviewed half a year ago, but with my 10x50 it occasionally shows up when the eye pupil is severely off-center. In dynamic situations such as panning over a night scene with city lights, the rainbow spikes keep flushing up and disappearing again. I have further seen them on bright astronomical objects such as the moon, Venus and Jupiter, Vega, but not on Aldebaran or fainter stars. Currently, the origin of this phenomenon remains unknown to me, but it is obviously caused by the prism due to its symmetry-breaking character. It shows up sufficiently rarely so that I won't really bother, but it is an issue to be addressed. This point goes to the Fujinon.

Chromatic aberration (CA): Both binoculars show some color fringing along edges of objects in the periphery of the field. With the Fujinon, it seems no longer as bad as I remember seeing it 20 years ago, since the peripheral image is sufficiently blurred to mask the true amount of CA. The blurriness is caused mainly by residual field curvature, and a re-focusing sharpens the peripheral sections and thus unveils the true amount of CA with the Fujinon. Once more I have to refer to the discussion below about observable aberrations and observer's age. The SRBC, despite being named 'APO', shows color fringing, too, and I see little difference in its quantity to the Fujinon. The point is split here, although - perhaps 20 years ago and with younger eyes - I might have given the point to the SRBC.

Fig. 5: The edge pupil is the exit pupil when seen from an angle at which the pupil is about to hit the edge of the eye lens. Here, it assumes a 'cat-eye' shape as a result of vignetting. The Fujinon (left) shows an unusual low degree of vignetting, but also a visible chromatic aberration of the exit pupil, the effect of which is unknown to me.

Low light performance: Since both binoculars have the same exit pupils of 5mm, and apparently similarly high transmissions, their low light performances are essentially the same. A comparison of the edge pupils suggests a lower degree of vignetting with the Fujinon (Fig. 5): I have measured the ratios of the smallest vs. the largest diameters (the aspect ratios) of the edge pupils and obtained 0.85 for the Fujinon and 0.7 for the SRBC. The latter seems to be rather common, and the Fujinon's low vignetting an exception, certainly made possible by its large oversized prisms which allow passage of almost the entire light bundle at all angles. Vignetting leads to a loss of image brightness at its periphery, but human perception is known to be rather insensitive to vignetting and it has been claimed that 30% or even 40% would remain practically invisible. I have used both contenders from sunset all the way into full darkness and frequently compared their brightness, without being able to decide which of them appeared brighter. Similarly, under the night sky when observing nebula and galaxies, I found these binoculars to deliver images of equal brightness. The point is split here.

Mechanical construction

Ruggedness: The SRBC is fully waterproof and covered by a rubber armor so that it should perform well under any weather condition. The Fujinon FMTR is a military grade binocular and designed to be used not only in astronomy but also in military, law enforcement and for other professional tasks. There are also decades of experience in professional application behind the Fujinon, and I would give this point to the Fujinon.

Summary

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

All in all, the SRBC 10x50 is the superior binocular in this comparison. This is not only true for general-purpose applications, but also for astronomy, which has always been the prime qualification of the Fujinon. The very wide field offered by the SRBC, in combination with its excellent sharpness, yields this extremely immersive image of star fields which, in the framework of handheld binoculars, is only topped by the Nikon WX. The SRBC further offers a sufficient degree of stray light (glare) protection to provide high performance under twilight condition when, e.g., observing a comet. Exceptions are very bright objects where the Fujinon still has the advantage. I still prefer the Porro prism binocular when observing the moon, since the huge contrast between the bright planes and shadowed craters is just perfectly reproduced with the Fujinon. Considering the fact that the SRBC is significantly more compact, much lighter, and also less expensive than the Fujinon, I would conclude that the SRBC is the better choice overall.

Remarks on the effect of the observer's age on the evaluation of binocular performance

These facts have to be kept in mind when binoculars are tested by various observers who differ considerably in age. Some of the controversies that are commonly fought out on the Internet discussion boards may be rooted in these age-related differences rather than in sample variations or by inaccurate assessments.

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