20x25 Foldable BAK4 Binoculars

Dimensions: 4.7 x 1.8 x 1.6 inches (folded); weight: 0.5 lbs (227 g); objective lens diameter: 25 mm; eyepiece diameter: 16 mm; magnification: 20x; field of view: 399 ft @ 1,100 yd; optical construction: BAK4 prisms with multi-coated aspherical lens elements; light transmittance: 99.68%; body material: shockproof soft silicone with non-slip rubber armour; IPX4-rated daily waterproof and fog-proof construction. Optical performance is grounded in precision engineering: aspherical lens elements correct spherical aberration inherently, while multi-layer broadband coatings minimise surface reflection losses across visible wavelengths — directly contributing to the measured 99.68% transmittance and resulting image brightness. BAK4 prisms ensure full light exit pupil utilisation, avoiding the greyish vignetting typical of BK7 equivalents. Built for resilience in variable UK conditions: the rubber armour withstands repeated drops onto grass, gravel or pavement; the sealed housing tolerates drizzle, mist and high-humidity environments like woodlands or coastal cliffs; the fold mechanism is tested for 5,000+ open/close cycles — ensuring long-term reliability far beyond disposable travel optics.