Nikon MONARCH 5 10×42 Binoculars: Verified Specs and Stargazing Guide

The original post on this site was a short Nikon MONARCH 5 10×42 product description. Nikon USA now lists this model as archived, but its specifications are still published. This rewrite uses those figures and explains what they mean for a beginner, including for night-sky use.

Verified specifications

From Nikon USA’s MONARCH 5 10×42 (product 7577) specifications:

• Magnification: 10x
• Objective diameter: 42 mm
• Real angular field of view: 5.5°; apparent field: 51.3°
• Field of view: 288 ft at 1,000 yards
• Close focus distance: 7.8 ft
• Exit pupil: 4.2 mm
• Eye relief: 18.4 mm
• Size: 5.7 x 5.1 in; weight: 21.6 oz
• Roof prism with phase coating and dielectric coating
• ED glass
• Waterproof and fogproof
• Central focus

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. Nikon lists 4.2 mm (42 ÷ 10), which suits most adult eyes at night.
• 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. 288 ft works out to about 5.5°, matching Nikon’s real-field figure. 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. With 18.4 mm of eye relief, the MONARCH 5 10×42 comfortably meets that, a plus for observers who wear glasses.

Is it good for stargazing?

The 42 mm lenses meet Astronomy magazine’s recommended minimum of 40 mm for astronomy, and 10x is the top of the range it suggests for hand-held use. That makes a 10×42 a sensible grab-and-go choice for the Moon, bright star clusters and the Milky Way. Astronomy magazine notes that roof-prism binoculars can give slightly dimmer images than Porro-prism models, and it says that the more lens and prism surfaces are coated, the brighter and higher-contrast the image; Nikon lists phase and dielectric coatings for this model. For long views, bracing your elbows or using a tripod adapter makes faint targets easier.

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 ED glass.
• 5.5° (288 ft) field; 4.2 mm exit pupil.
• 18.4 mm eye relief suits glasses wearers.
• 21.6 oz; 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.