Those readers familiar with my Binocular Universe column may recall my monthly sign-off line, “Two eyes are better than one.” That’s not just a cliché; that’s my mantra. Ever since I became interested in astronomy, binoculars have been by my side. While I have owned many telescopes over the decades, binoculars have remained an important part of my equipment arsenal.
That’s why I was especially excited to review Oberwerk’s 20x65 ED Deluxe binoculars. Oberwerk, German for “above work,” broke onto the scene in 1999 as a small online retailer founded by Kevin Busarow. More than two decades later, Oberwerk continues to market quality binoculars for every budget.
Breaking them down
The 20x65 ED Deluxe binoculars, introduced about three years ago, are built around a unique combination of 65mm-diameter objective lenses and 20x magnification. Most 20x binoculars come with 80mm objectives, although a few have 70mm and even 60mm objectives. The smaller 65mm aperture will produce slightly dimmer images. Together, they help to darken the field and improve image contrast, especially in areas suffering from light pollution, thanks to the smaller 3.25mm exit pupil.
Optically, the heart and soul of the 20x65s are twin f/6 objective lenses. The objectives feature a two-element design, one of which is made from extra-low dispersion (ED) glass. As with refracting telescopes, binoculars that use non-ED objectives suffer from color fringing around bright objects, caused by chromatic aberration. ED glass delivers sharp images free of this false coloring.
Like all better-quality binoculars using the Porro prism design, the Oberwerk 20x65s feature prisms made of BaK 4 (barium crown) glass. BaK-4 prisms transmit brighter, sharper images because nearly all the light that enters the prism assembly is reflected along the intended optical path; very little light is lost. This is what optical designers call “total internal reflection.”
The eyepieces are a modified-Erfle design using five lens elements set in three groups. They produce an apparent field of view measuring 65°, with a real field spanning 3.2° of sky.
The 20x65s are fully broadband multi-coated, meaning every air-to-glass surface — from lenses to prisms — has multiple layers of broadband coatings that improve light transmission and suppress flaring. The waterproof barrels are sealed, purged, and filled with dry nitrogen to prevent internal fogging, even in damp conditions.
Adding all this together, the 20x65s have all the right stuff optically.
Mechanically, the binoculars are also well made. They feature two-tone aluminum barrels measuring 15 inches (38.1 cm) long, including the eyepieces. That’s a little longer than a 2-liter soda bottle. The barrels are 8.5 inches (21.6 cm) wide. The back halves of the barrels are dark olive green with a thin rubber armor coating, while the front halves toward the objectives are painted black. The barrels feature ergonomic hand grips around the prisms but, given the dimensions and weight (6.4 pounds [2.9 kilograms]), the 20x65s need to be mounted on a tripod or other external support for best results. Believe me, I tried.
But Oberwerk obviously doesn’t expect you to hold them up by hand like traditional binoculars. They wisely incorporated a sliding tripod mount on a central rail between the two barrels, allowing the user to balance the binoculars on their mount. Since the mount attaches directly to a tripod head, an L-shaped tripod adapter is not necessary.
To ensure that no nitrogen leaks out of the barrels, the 20x65s feature individually focused eyepieces. Focusing is precise, requiring just the right amount of effort to turn the eyepieces. When I tried them, there was no backlash or wobble when focusing. The eyepieces proved comfortable to view through, thanks in part to foldable rubber eyecups around each.
The eyepiece cups must be folded back if you need to wear eyeglasses for viewing. According to Oberwerk, the 20x65s have 18mm of eye relief, which is the distance from an eyepiece’s outer lens that you must position your eye to take in the full field of view. The Oberwerk eyepieces are recessed in their housings by 0.11 inches (3 mm), reducing the available distance to 15mm. I normally observe without glasses, even though I am nearsighted. To test the binoculars’ viewing comfort, however, I tried viewing with my glasses on and found that I had no trouble seeing the entire field.
To take in that full view, a binoculars’ interpupillary distance (IPD) must be adjusted to match the distance between the observer’s eyes. In the case of the 20x65s, the IPD can accommodate a range between 2.2 to 2.9 inches (5.6 to 7.4 cm), a good range of adjustment.