Binoculars are Singular!

Bino Basics

Now we’d call it a Porro-prism binocular — a nod to Italian optics guru Ignazio Porro, who had also pioneered the design. It’s distinguished by a “stepped” profile, the barrels offset from the eyepieces. More popular now: the roof-prism binocular, whose front and rear lenses share an axis. That design dates to 1897 work at M. Hensoldt & Sohne (later absorbed by Zeiss) in Wetzlar, Germany.

Note my use of “binocular.” A binocular has two barrels (hence: “bi”). Hunting, I carry just one binocular, though I own several. Because I don’t have four eyes, a pair of binoculars would be no more useful on the trail than four shoes.

My first binocular was a second-hand Bausch & Lomb Zephyr, a 7×35 glass lauded by legions of hunters (including Jack O’Connor) in the 1950s and ’60s. Delightfully lightweight at 19 oz., it came dear. In 1952, when a Winchester Model 70 listed for $126.50 and a Savage 99 for $111.50, that Zephyr fetched $155! While it’s been surpassed optically by top-tier binos with coatings that trim aberrations and yield incrementally brighter images, I doubt I’ve seen any game with new glass that wouldn’t have come to eye as quickly with my old B&L!

As a Porro-prism binocular, that 7×35 is less compact than an equivalent roof-prism model; but in theory the wider objective spacing enhances “binocular vision,” which helps us gauge distance.

The late optics authority Walter Mergen told me when he was at Zeiss, top-quality binoculars contain several types of glass. “None are to save cost. All do specific jobs. Flint glass is heavier and more brittle than crown glass so is ill-suited to external lenses. But inside it helps deliver the best images.”

Light entering a roof-prism binocular is “split” into color bands. Zeiss was first with lens coating that brings the bands back “into phase” to prevent color fringing. Now phase correction is common across binocular brands. It is not needed in Porro-prism binoculars.