Review: Leupold BX-4 Pro Guide 10x42 binoculars

Leupold’s new 10×42 Pro Guide binocular is a high-quality optic offering spectacular optical performance in a compact package, and if topflight optics, mechanical reliability, armour, superior resolution, contrast and lack of aberrations are worth the price, then this Leupold deserves significant consideration.

In my estimation, a high-quality binocular is just as important to a hunter as his firearm. I can’t imagine hunting any kind of big game without one, and can’t think of a single hunt where I could have done without it.

Leupold BX-4 Pro Guide binoculars review — The Pro Guide 10×42 is lightweight thanks to an open-bridge design and compact size

When used in open country, a 10x binocular enables the hunter to see game at great distances even when it is partially hidden by brush or lying in the shade of rocks. Contrary to what we are told, a more powerful glass than a 6x will not handicap you at close distances.

Leupold specifies a field of view of 99.4m at 1000m and since this is an angular measurement, it is 10 times greater at 1000m than at 100. Thus, its field of view at 500, 100 and 50 metres is just shy of 50, 10 and 5m respectively. I’ve never found the 10×42’s width of field at the closer ranges a hindrance in timber.

A binocular with a 42mm objective is just about as heavy a glass as you can hang from your neck without a harness. Weight of the Leupold is 680g, which is among the lightest, making it ideal for mountain hunting. Leupold pared weight by using an open-bridge dual-hinge design that’s more comfortable to grasp.

The Pro Guide roof-prism binocular is rubber armoured which not only protects the binocular from being damaged as it bangs against the rifle or rocks as it swings about during a climb. The barrels are a shadow grey colour and the armour is pebbled to afford a sure grip with cold hands.

Rubber armour helps make it waterproof, too. Leupold’s Guard-ion exterior lens coating sheds water to show a clean image in wet conditions. Leupold’s experience in making absolutely waterproof rifle scopes has carried over into binocular manufacture.

Waterproofing, by the way, is not fog-proofing. Nitrogen gas, introduced under vacuum, prevents interior fogging, making the Pro Guide truly waterproof and fog-proof.

Other features I like are the large twist-out eyecups that are also pebbled. These replace the traditional fold-down rubber eyecups and you can press them against your brow when glassing without having them collapse.

I also like the Leupold’s internal centre-focus adjustment over models with individual focus simply because they are faster to adjust while I hold the binocular to my brow. Another good feature is the long 16mm eye relief.

High-definition (HD) glass has been introduced into the Leupold’s objective lens system. The purpose of HD glass is to get the optimum contrast of images in view and minimise colour fringing. Some manufacturers of cheap binoculars do this by simply adding fluoride to a specific lens. Leupold has taken this a step further by tweaking certain glass types with other coating technology in the HD lens to obtain contrast that cannot be achieved by the use of fluoride alone.

Fully multi-coated lenses transmit light more efficiently to offer a clearer view, and are phase corrected to prevent colour fringing, something necessary on roof prism binoculars.

The twilight factor (TF), is a mathematical expression of resolution in poor light (square root of the product of magnification and objective diameter). The TF value is 20.5 in the Leupold 10×42, which has an exit pupil of 4.2mm. This is a practical minimum since a smaller exit pupil won’t let in enough light at dawn and dusk.

The pupil of the human eye varies in diameter in response to the intensity of light entering it, from approximately 2.5mm during bright sunlight to a maximum of about 7mm in total darkness. Just before dark on a clear day the pupil opens to a diameter of about 5mm. An exit pupil of 3mm is plenty for hunting on a bright day, but the Pro Guide’s 4.2mm exit pupil transmits about all the light an eye can use even on a cloudy day.

I tested the Leupolds by observing kangaroos and deer grazing on the flat in front of my house from late evening up to dark. The flat is fringed on one side by brush and pine tress that throw dark shadows.

The Leupolds allowed me distinguish detail and pick up animals I could barely resolve with my naked eye. Although a binocular can’t manufacture light, this 10×42 definitely brightened the dark places where the deer lurked.

Optic makers can increase the amount of light in a specific area of the light spectrum to correct unnatural tinting so that the user sees not only a lot of light, but the correct colour of light as well. Leupold’s more advanced Elite Optical system features lens coatings of alternate layers of metal oxides — aluminium oxide, titanium oxide and silicon oxide.

Each oxide manipulates a specific wavelength of light and works in concert to increase the contrast between certain colours — like the brown of animal fur and the green of tree leaves — to give a hunter searching for game a real advantage.

Looking through the Pro Guide into shadows, at areas of bright sunlight and at various colours, you quickly see the difference in resolution and dispersion (colour resolution).

I ran a check for peripheral distortion by viewing fences and the tin roofs of buildings with straight lines, panning the glass so they eased out of the field of view. I’m pleased to report that all the lines stayed straight and sharp in detail.

The Leupold Pro Guide acquitted itself well in a comparison test with my expensive top-of-the-class 10×42 Leica, in terms of brightness, resolution and glare reduction. I believe it will be a significant player in the medium price range, and in the hunter’s scheme of things.

SPECIFICATIONS