Explore Scientific BT-100 National Geographic Expedition Series Binoculars

Description

Mounted on high-altitude viewing platforms and dark-sky field camps, the Explore Scientific BT-100 National Geographic Expedition Series Binoculars deliver high-contrast stereoscopic resolution for deep-space astronomy and ultra-long-range terrestrial surveillance. Equipped with supplied 20mm 62-degree LER eyepieces producing 28x magnification, this large-aperture instrument provides a 2.3-degree actual angle of view (62-degree apparent field), a 3.6mm exit pupil, and 15mm of eye relief for resolving lunar crater walls, planetary structures, and distant geographical landmarks.

The optical system incorporates 100mm semi-apochromatic doublet objective lenses with a 550mm focal length, paired with oversized BaK-4 Porro prisms and broadband fully multi-coated surfaces for optimized light transmission and color fidelity. Measuring 520 by 270 by 155mm (20.5 x 10.6 x 6.1 inches) and weighing 6.8 kg (15 lbs), the chassis is cast from lightweight magnesium-aluminum alloy and sealed to IPX6 water-resistant standards with dry nitrogen gas filling to prevent internal fogging. Eyepiece barrels are inclined at a 45-degree angle to provide comfortable viewing when observing zenith sky regions, controlled by independent helical focusers with brass compression rings that accept standard 1.25-inch eyepieces, an interpupillary distance range from 54mm to 76mm, sliding aluminum dew shields, an integrated carry handle, and a bottom mounting plate with 1/4-20 and 3/8-16 threaded sockets.

Key Features of Explore Scientific BT-100 National Geographic Expedition Series Binoculars

Built for binocular stargazing and expedition-level terrain observation, this 100mm giant binocular combines semi-apochromatic doublet optics with 45-degree angled oculars. Its broadband multi-coated lenses and oversized BaK-4 Porro prisms produce bright, high-contrast imagery of planetary targets and deep-sky nebulae. The nitrogen-purged IPX6 water-resistant chassis mounts securely on heavy tripods and alt-azimuth fork heads via its dual-threaded mounting base.

• 28x standard magnification using supplied 20mm eyepieces paired with light-gathering 100mm objective lenses
• Porro prism optical architecture incorporating oversized BaK-4 optical prisms for complete field illumination
• Semi-apochromatic doublet objective lenses delivering sharp color correction across a 550mm focal length
• Wide 62-degree apparent field of view with an actual angular field of 2.3 degrees at 28x
• Comfortable 15mm eye relief and 3.6mm exit pupil with soft rubber eyecups on 1.25-inch oculars
• Independent helical eyepiece focusers with brass compression rings for standard astronomical oculars
• Airtight nitrogen-purged magnesium-aluminum chassis certified to IPX6 water-resistant standards
• Integrated carry handle and bottom mounting foot with 1/4-20 and 3/8-16 threaded tripod sockets

100mm Semi-Apo Doublet Glass & BaK-4 Porro Prisms

The 100mm objective lenses gather extensive photon volume, generating a 3.6mm exit pupil that renders faint celestial targets with sharp contrast against dark night skies. Semi-apochromatic doublet optical elements control chromatic aberration across high-contrast borders, such as the bright lunar limb and planetary disks. Oversized BaK-4 Porro prisms provide complete optical throughput to the ocular holders, preventing edge vignetting and maintaining illumination across the entire 62-degree apparent field.

Magnesium-Aluminum Chassis & 45-Degree Viewing Ergonomics

The magnesium-aluminum alloy chassis keeps total tube mass to 6.8 kg, providing structural rigidity to maintain factory collimation alignment while remaining portable for field expeditions. The 45-degree angled ocular orientation allows observers to study zenith celestial targets without experiencing neck fatigue. Retractable metal dew shields slide forward to block stray peripheral light and prevent dew formation on the objective lenses, while dual independent helical focusers permit precise focal adjustments for each eye.

• Dual independent helical focus collars with brass compression rings for secure eyepiece clamping
• Nitrogen-purged IPX6 water-resistant chassis engineered to withstand heavy outdoor dew and rain
• Built-in 45-degree angled eyepiece receptacles and integrated top handle for safe transport and setup

Explore Scientific Manufacturer Warranty & In-Box Inclusions

The Explore Scientific BT-100 National Geographic Expedition Series Binoculars are backed by the Explore Scientific limited warranty covering optical and structural components against manufacturing defects. The complete factory package contains the Explore Scientific BT-100 National Geographic Expedition Series binocular body, pair of 20mm 62-degree LER eyepieces (28x), extendable dew shields, objective lens covers, eyepiece caps, and heavy-duty foam-lined transport case.