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Explore Scientific

BT-70 SF Large Binoculars with 62 Degree LER Eyepieces

$1,299.99 USD $1,699.99 USD
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BT-70 SF Large Binoculars with 62 Degree LER Eyepieces
$1,299.99 USD
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BT-70 SF Large Binoculars with 62 Degree LER Eyepieces

Description

The Explore Scientific BT-70 SF is a premium giant binocular built for serious astronomy enthusiasts and dedicated terrestrial observers who demand the best in optical performance. With 70mm objective lenses and a 400mm focal length, this binocular delivers bright, high-contrast views of the moon, planets, deep-sky objects, distant wildlife, and sweeping landscapes. Each eye benefits from its own complete optical system, creating an immersive, three-dimensional viewing experience that dramatically reduces eye fatigue during long observing sessions.

The BT-70 ships with two 62-degree 20mm LER (Long Eye Relief) eyepieces for 20x magnification right out of the box, and its standard 1.25" eyepiece compatibility lets you dial magnification anywhere from 15x to 50x. A rugged magnesium housing with IPX6 waterproofing and nitrogen purging ensures the optics stay fog-free and protected in demanding outdoor conditions - making this an instrument built to perform season after season.

Key Features

  • 70mm Objective Lenses: Large aperture gathers abundant light for bright, detailed views of celestial and terrestrial subjects.
  • 400mm Focal Length / f/5.7: Delivers a wide, bright image with strong contrast across astronomy and nature observation.
  • Included 62° 20mm LER Eyepieces: Two premium Long Eye Relief eyepieces provide 20x magnification and a 3.1-degree true field of view for comfortable, immersive viewing.
  • 1.25" / 31.7mm Interchangeable Eyepiece Compatibility: Swap in any standard 1.25" eyepiece to adjust magnification from 15x to 50x for deep-sky or high-power planetary work.
  • Achromatic Refractor Porro Optical Design: Enhanced Multilayer Deposition (EMD) coatings maximize light transmission and deliver sharp, high-contrast images.
  • IPX6 Waterproof & Nitrogen-Purged Magnesium Housing: Fully weatherproof construction prevents internal fogging and withstands rugged outdoor use.
  • 45-Degree Viewing Angle: Ergonomic angled eyepiece design allows relaxed, fatigue-free observation - especially important during extended astronomy sessions.
  • Extendable Dew Caps: Help shield objective lenses from dew and stray light for cleaner views in humid or nighttime conditions.
  • Fine Helical Focus: Smooth, precise focus control for sharp images even at high magnification.
  • Tripod & U-Mount Compatible: Features an integrated carrying handle and standard mount interface - pair with a sturdy photo tripod or the optional Explore Scientific U-Mount with Field Tripod for a rock-steady platform.

Options & Which to Choose

  • 70mm (BT-70): The most compact and lightweight of the lineup, the 70mm is ideal for observers who want portability without sacrificing serious optical performance. A great entry point into giant binocular astronomy and a versatile choice for both stargazing and daytime terrestrial use.
  • 82mm: Steps up aperture for noticeably brighter images and better resolution on faint deep-sky objects and fine terrestrial detail. A strong all-around choice for dedicated astronomy enthusiasts who want more light-gathering without a dramatic increase in size or weight.
  • 100mm: Delivers a significant aperture upgrade suited to observers focused on deep-sky astronomy - galaxies, nebulae, and star clusters come alive with greater detail and contrast. Best for those with a stable, heavy-duty mount who want near-telescope-level views in a binocular format.
  • 120mm: The most powerful configuration in the BT series, offering maximum light-gathering capability for serious deep-sky and planetary observers. Ideal for astronomers with a permanent or semi-permanent setup who want the ultimate binocular viewing experience.

What's Included

  • Explore Scientific BT-70 SF Giant Binocular
  • Two 62-degree 20mm LER Eyepieces (1.25")

Why You'll Love It

The BT-70 SF represents a genuine leap in observing comfort and optical quality for anyone serious about astronomy or high-performance nature observation. Unlike standard binoculars, the BT-70's dual full optical systems and 45-degree viewing angle let you observe for hours without the neck strain or eye fatigue that plagues traditional designs. The all-weather magnesium chassis and IPX6 waterproofing mean you can take it to dark sky sites, mountain overlooks, or coastal wildlife refuges without worry. The flexibility to swap eyepieces across the full 1.25" standard means your accessory investment grows with your interests. Trusted by astronomy enthusiasts and nature observers who refuse to compromise, the BT-70 SF is an instrument you'll reach for night after night - and one that's built to last for years of demanding use.

Product Specifications

View Product Specs
Item Number 01-14200
Optical Design Achromatic Refractor Porro
Objective Lens Diameter 70 mm
Focal Length 400 mm
Focal Ratio f/5.7
Apparent Field of View 62 degrees
True Field of View 3.1 degrees
Magnification (Included Eyepieces) 20x
Magnification Range (1.25" Eyepieces) 15x - 50x
Exit Pupil (Min) 3.5 mm
Eye Relief 15 mm
Coating Enhanced Multilayer Deposition (EMD)
Waterproof Yes - IPX6
Housing Material Magnesium
Total Length 370 mm
Total Width 213 mm
Total Height 122 mm
Net Weight 3,400 g

FAQ

Do I need a tripod to use the BT-70?

A tripod is strongly recommended. At 20x magnification and above, even slight hand movement becomes very noticeable, making handheld use impractical for most observers. The BT-70 features a standard tripod mount interface and integrated carrying handle, and pairs perfectly with a sturdy photo tripod or the optional Explore Scientific U-Mount with Field Tripod for a stable, fully adjustable platform.

Can I use my existing 1.25" telescope eyepieces with the BT-70?

Yes - the BT-70 is fully compatible with all standard 1.25" (31.7mm) eyepieces, which is the most common eyepiece format in amateur astronomy. This means you can use eyepieces you already own or easily expand your collection to access magnification from 15x all the way up to 50x. Optional color and nebula filters in the same 1.25" format can also be used to enhance contrast on specific astronomical targets.

Is the BT-70 suitable for daytime use, or is it just for astronomy?

The BT-70 is an excellent daytime observer as well. Its 70mm aperture, bright optics, and 45-degree viewing angle make it ideal for birdwatching, wildlife observation, scenic overlooks, and sporting events - anywhere you want an immersive, high-magnification view of distant subjects. The IPX6 waterproof rating also makes it well-suited for outdoor use in variable weather conditions.

What is the difference between the BT-70 and the larger BT models (82mm, 100mm, 120mm)?

The primary difference between models is aperture size, which directly affects light-gathering ability, image brightness, and resolution of fine detail. The 70mm is the most portable option and delivers excellent performance for most observers. As aperture increases through the 82mm, 100mm, and 120mm models, images become progressively brighter and more detailed - particularly on faint deep-sky objects like galaxies and nebulae. Larger models also require a more substantial mount to support their increased size and weight.

What does "nitrogen-purged" mean, and why does it matter?

Nitrogen purging means the interior of the binocular has been filled with dry nitrogen gas and sealed. This eliminates moisture inside the optical tube, which prevents internal fogging when you move between temperature extremes - like bringing the binocular from a warm car into cold night air. Combined with the IPX6 waterproof seal, nitrogen purging ensures the optics stay clear and protected throughout years of outdoor use.
Color pattern Silver
Magnification 50x
Material Metal
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