Review of four 15x56 binoculars
9. Night tests
When it comes to astigmatism, one could argue we have a bit of a surprise: the most affordable model, the Oberwerk, performed best, while the most expensive, the Swarovski, finished last. However, looking closer at the details reveals that this twist is not quite as unexpected as it might seem. First, the Oberwerk is a straightforward, efficient Porro prism design tailored primarily for astronomy - so it comes as no surprise that ensuring pinpoint star images was a key design priority. Second, on a 10-point scale, the Oberwerk scored nearly 9 points compared to the Swarovski's 7.5 - making the actual gap quite small. Sitting in between are the Zeiss, which trails the Oberwerk slightly, and the Sky Rover, which holds a subtle edge over the SLC.
Identifying the frontrunners for edge vignetting was straightforward. Indeed, the Swarovski and the Zeiss turned in the best performance, having the easiest task due to possessing the narrowest - and virtually identical - fields of view. The Oberwerk took the next spot, followed by the Sky Rover. Yet even with the Sky Rover's vast field of view, the level of edge darkening could hardly be considered significant.
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The third subcategory was coma, where the Swarovski claimed top honors. In its case, minor elongation of star images becomes visible in the so-called "Absam ring" located at around 80% of the field radius. Near the field stop itself, coma remains very low.
Second place fell to the Zeiss, where coma manifests at roughly 70% of the field radius and reaches the boundary between low and moderate levels at the outermost edge.
The Sky Rover secured third place; its coma appears slightly further out than on the Zeiss, but grows noticeably larger right at the edge. The Oberwerk fared worst in this regard, with coma appearing earliest in the field and reaching the highest level at the edge.
The final verdict for the nighttime tests places the Zeiss in the lead, followed by the Swarovski in second, the Oberwerk in third, and the Sky Rover in last place.
This marks the first category in which the Banner Cloud landed in last place, though that should hardly come as a shock. For one, it had by far the largest field of view to correct; for another, it is the only binocular in this test to rely on Schmidt-Pechan prisms, which demand reflective mirror coatings, require an air gap, and involve six light reflections. All of these optical factors inevitably left their mark during nighttime testing.
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