Simmons ProSport 10×42 Roof-Prism Binoculars: Specs and Beginner Guide

The original post on this site was a short product description of the Simmons ProSport 10×42 waterproof binocular. Simmons’ official page for the line is no longer online, so this rewrite uses the specifications Simmons released when it added five new ProSport models in 2011, as published by AmmoLand.

Verified specifications

From Simmons’ ProSport announcement (April 2011), for the 10×42 models 899431 (black) and 899441 (camo):

• Magnification: 10x; objective diameter: 42 mm
• Roof prism system with BAK-4 prisms
• Multi-coated optical glass
• Field of view: 303 ft at 1,000 yards
• Eye relief: 16 mm
• Exit pupil: 4.2 mm
• Weight: 23.8 oz
• Twist-up eyecups
• Nitrogen purged for waterproof and fogproof performance
• Rubber armour
• Other models in the 2011 line: 8×42, 10×50 and 12×50

Corrections to the original listing

• The published table labels field of view as “ft. @ 100 yds”. At 100 yards, 303 ft would be a view about 54° wide, far beyond any binocular; the figure only makes sense as feet at 1,000 yards, the industry standard, so we have corrected the unit.

What the numbers mean

Every binocular carries two numbers. Astronomy magazine’s binocular guide explains that the first is the magnification and the second is the diameter of each front lens in millimetres, so a 10×42 magnifies 10 times and has 42 mm lenses.

• Exit pupil: aperture divided by magnification. 42 ÷ 10 gives 4.2 mm, as Simmons lists.
• Why exit pupil matters at night: the same guide says most people under 30 have dark-adapted pupils of about 7 mm, around 6 mm in their 30s, and probably no more than 5 mm from age 40. A bigger exit pupil than your eye can use simply wastes light.
• Field of view: to convert feet at 1,000 yards into degrees, divide by 52.5. 303 ft works out to about 5.8°. Astronomy magazine says most binoculars cover about 6° to 7°, high-power models 3° to 5°, and wide-angle models 8° to 10°.
• Eye relief: Nikon’s guide says eye relief of 15 mm or longer lets most eyeglass wearers see the whole field without removing their glasses. At 16 mm, the ProSport 10×42 meets that guideline.

Is it good for stargazing?

With 42 mm lenses and 10x magnification, this binocular sits right in the range Astronomy magazine recommends for hand-held stargazing: at least 40 mm aperture and no more than about 10x. Expect good views of the Moon, bright clusters and the Milky Way. Astronomy magazine also notes that BaK-4 prisms, as listed for the ProSport, are found in most higher-quality binoculars, and that more coated surfaces give brighter, higher-contrast images.

Setting up your binoculars

Bushnell’s Trophy owner’s guide describes the standard set-up that works for most centre-focus binoculars:

• Eyecups: twist them up if you do not wear glasses, so your eyes sit at the right eye relief distance and you see the full field of view.
• Interpupillary distance: point the binoculars at a blank wall or sky and move the two halves closer or farther apart until you see a single circle with no shaded areas.
• Focus the left side: cover the right objective lens, then turn the centre focus knob until a detailed distant object looks sharp through the left side.
• Set the diopter: cover the left lens instead and turn the diopter ring under the right eyepiece, not the centre knob, until the right side is sharp.
• Remember your setting: note the diopter mark so you can reset it if someone else uses your binoculars.

What you can see in the night sky

According to Astronomy magazine, binoculars show the Moon in crisp detail, including shadows moving across lunar features as it waxes and wanes and earthshine on a crescent Moon. They also let you follow the phases of Venus and the motions of Jupiter’s big moons. Beyond the solar system, large star clusters such as the Pleiades in Taurus and the Beehive in Cancer fit nicely in a binocular view, and the Andromeda Galaxy (M31) stands out from a dark site. The magazine says more than 400 deep-sky objects lie within reach of good binoculars from a dark-sky site.

Care and cleaning

The Trophy guide’s cleaning advice applies to any binocular: blow or brush away dust first, then wipe in a circular motion with a microfibre cloth. For a thorough clean, use photographic lens tissue and lens-cleaning fluid, always applied to the cloth and never directly on the lens. Never use household window cleaner or paper towels, which can damage coatings or scratch the glass. Store the binoculars in a cool, dry place.

Safety

Never look at the Sun through binoculars or any optical instrument. Bushnell’s guide warns this may permanently damage your eyes.

Quick summary

• 10×42 roof prism with BAK-4 prisms.
• 303 ft field (about 5.8°); 4.2 mm exit pupil.
• 16 mm eye relief; 23.8 oz.
• Nitrogen purged, waterproof and fogproof.

Jargon buster

• Objective lens: the big front lens that collects light.
• Exit pupil: the small bright circle of light you see in each eyepiece when you hold the binoculars away from your eyes.
• Diopter: an adjustment for differences between your two eyes.
• Roof vs Porro prism: roof models have straight barrels; Porro models have the classic zigzag shape.