The Russian Tento 20x60s became a favorite with astronomers in the 1970s, despite their tiny eye relief, but they have been out of production for several decades. Will Pentax’s 20×60 WP binoculars tick all the right boxes?
Pros: Good image quality, innovative focus mechanism
Cons: Small field of view, poor accessories.
The first things that strike you when you unpack these Pentax 20×60 binoculars is their unusual construction. Unlike other center-focus Porro-prism binoculars, the focus mechanism is internal. This confers two advantages. Firstly, it makes them much easier to waterproof; these are specified as JIS Class 6 with nitrogen filling. The second feature is a Pentax innovation: you can slide the focus-wheel forward to lock the focus, so once you have achieved perfect focus, you won’t accidentally shift it.
The other thing that you’ll notice is that the case is thin and strapless, and that the lens caps simply will not stay on. Fortunately, the quality of the binoculars themselves compensates for these shortcomings.
20x is too much to hand-hold steadily, so you will need to mount these. They weigh only 3 lbs (1.4 kg), so they are not very demanding of the mount, making a monopod ideal if you want to preserve portability. Mounted, they are lovely to use. They only have a small field of view (2.2 degrees), but this is extremely sharp over the central 95 percent; similarly-priced binoculars may have a wider total field of view, but the sharp proportion will be smaller. There are effective light baffles in the objective tubes, and the color rendition is excellent. There is some color fringing if you have the lunar limb or terminator near the edge of the field.
These won’t be your binocular of choice for enjoying wide vistas or teasing out faint deep sky objects (although they are no slouch at these), but they really come into their own when you have targets that demand sharp optics and/or good color rendition.
Panning around the lunar terminator is a joy, and open clusters that are mere fuzzy blobs in 10x50s may resolve into stars. You can see structure in the Andromeda Galaxy (M31), Saturn has an actual ring, and colored star groups like the Meissa cluster in Orion are vibrant. The optical quality is such that Albireo shows dark sky between its components right to the edge of the field of view, and I could distinguish three of the Orion Nebula’s Trapezium stars, suggesting that the binoculars will resolve 13 arcseconds but not 8.5 arcseconds.
I found that the tapered tops of the twist-up eye-cups were comfortable in my eye sockets, and there is more than enough eye-relief if you need to use eyeglasses. With a close focus of 26 feet (8 m), they are also useful as birdwatching binoculars.
Full review by the author: http://binocularsky.com/binoc_reviews.php