The Sightron SIII 10x50 ED Binocular (SKU: SI-25182) is a roof-prism optical instrument designed for mid- to long-range observation in open terrain. Featuring extra-low dispersion (ED) glass elements, phase-corrected BAK-4 roof prisms, and fully multi-coated lenses, it minimises chromatic aberration while delivering high contrast across a 316.7-foot field of view at 1,000 yards. Built with a nitrogen-purged, O-ring sealed magnesium alloy chassis, this optic provides fully waterproof and fog-proof performance without requiring electronic circuits, batteries, or external power sources.

Key Features

• ED Glass Optical System: Integrates extra-low dispersion glass to reduce colour fringing and maintain edge-to-edge clarity during observation.
• Low-Light Aperture: Large 50 mm objective lenses and an optical design yielding approximately 90% light transmission produce a 5.0 mm exit pupil and a twilight factor of 22.4 for dusk and dawn viewing.
• Durable Magnesium Housing: Enclosed in a rugged, nitrogen-purged magnesium alloy body that prevents internal fogging and withstands full weather exposure.
• Tripod Mounting Interface: Features a standard 1/4"-20 front hinge adapter thread to support stationary tripod mounting for stable, extended glassing sessions.
• Adjustable Eyecups: Twist-up/down eyecups paired with 18 mm of eye relief accommodate users observing with or without spectacles.

Specifications

• Magnification: 10x
• Objective Lens Diameter: 50 mm
• Prism Type: BAK-4 roof prism with phase correction coating
• Field of View: 316.7 ft at 1,000 yards
• Eye Relief: 18 mm
• Exit Pupil: 5.0 mm
• Close-Focus Distance: 9.9 ft (approx. 3.0 m)
• Physical Length: 5.86 in (approx. 149 mm)
• Weight: 31.4 oz (approx. 890 g)
• Chassis Material: Nitrogen-purged magnesium alloy (waterproof and fog-proof)
• Tripod Mount: Threaded for standard 1/4"-20 binocular adapters

Who is the Sightron SIII 10x50 ED Binoculars for?

• Open-country deer and pest stalkers — Benefits from the 50 mm objective lenses and 10x magnification, which deliver a twilight factor of 22.4 to resolve targets across ridgelines and paddocks during dawn and dusk.
• Stationary target spotters and observation operators — Uses the 18 mm eye relief and standard 1/4"-20 tripod adapter thread to maintain stable, fatigue-free long-range viewing over extended surveillance periods.

Less suitable for: Mobile, high-cadence stalkers and multi-day alpine hikers where the 31.4 oz (890 g) chassis can cause neck fatigue, making lighter 8x32 or 8x42 binoculars under 700 g a better fit; or tight bushland hunting requiring focus under the 9.9 ft (3.0 m) close-focus threshold, where a dedicated compact optic is better suited.