Explore Scientific BT 150mm ED Giant Binocular

Two 150mm objectives, each a 2-element FK-61 ED doublet working at 840mm f/5.6, put the BT 150mm ED among the few genuine six-inch binocular telescopes in production. The APM 150mm 45-degree ED-APO is built on the same FK-61 glass and a similar magnesium body; Explore Scientific purges this one with argon instead of nitrogen and backs it with free adjustment, cleaning and collimation service for as long as you own the instrument. This is the largest aperture Explore Scientific builds for two-eyed observing, and at 41 pounds bare it is an installation rather than a grab-and-go.

Key Features

• Dual 150mm FK-61 ED doublets. FK-61 sits in the fluorine crown family and delivers chromatic correction comparable to Ohara FPL-51, which is what keeps the lunar limb and bright stars free of the violet fringing that a six-inch achromat at this focal ratio would show.
• 840mm focal length at f/5.6. With the supplied 62-degree 20mm eyepieces that works out to 42x over a 1.5-degree true field, wide enough to frame the Double Cluster whole while still resolving it.
• Rated to 100x by Explore Scientific. The 1.25-inch eyepiece holders take any standard eyepiece, so an 8mm pair puts you at 105x for lunar and planetary work, at the top of the range Explore Scientific guarantees for image quality.
• EMD coatings on every optical surface. Enhanced Multi-Layer Deposition across all air-to-glass surfaces, the same coating family used on the rest of the BT line.
• Argon-purged magnesium alloy chassis. Argon molecules are larger than nitrogen and leak past seals more slowly, which is the practical argument for it on an instrument that will spend years going from a warm house into cold night air.
• Individual eyepiece focus. Each side focuses independently, so you set your own diopter once and leave it. There is no center focus wheel to drift.
• Extendable dew shields and an integrated hand grip with sighting shoe. The shields pull out over the objectives against dew and stray light, and the handle carries a finder shoe so you can aim something this long without sighting down the tubes.

Ideal For

Deep-sky sweepers who want the Milky Way at 42x with both eyes. Two-eyed observing raises the effective contrast on faint extended objects over a single tube of the same aperture, which is why the large open clusters, the Veil, and the North America Nebula are where this instrument earns its keep.

Observers who tire at a single eyepiece. Long sessions are noticeably easier on two eyes. If you already know you close one eye and squint through a session, a binocular telescope changes the ergonomics of the whole night.

Permanent and semi-permanent setups. At 804mm long, 371mm across the dew caps and 41 pounds bare, this is an instrument for an observatory, a deck, or a pier. Mounting and dismounting it is a two-person job.

Long-range daytime and marine watching. The angled eyepiece design keeps targets at low to medium elevation comfortable to hold for long stretches, and 150mm of aperture holds detail at distances where a spotting scope starts running out of light.

Accessories & Compatibility

Mounting is the part to plan first. This binocular weighs 18.7 kg (41.1 lb) without eyepieces or case and measures 371mm across the dew shields, so it needs a mount and tripod rated well beyond a conventional binocular fork. Confirm both the load rating and the maximum binocular width against those figures before ordering a mount. If you want a smaller instrument that pairs with a standard binocular mount, the BT-70 SF makes the opposite trade: an achromatic 70mm at 7.5 pounds that one person can carry out and set up in a minute.

Eyepieces. The 1.25-inch holders accept any standard eyepiece, and magnification is 840 divided by the eyepiece focal length. Buy them in matched pairs. Interpupillary adjustment runs 61mm to 75mm.

Threads and fittings. The tripod adapter carries both 1/4"-20 and 3/8" photo threads. The dew shield internal thread is M169 x 1.5-6H for filters or accessories at the front of the tubes.

In the box. The binocular ships with its handle and tripod adapter, front and rear dust caps, the pair of 62-degree 20mm waterproof eyepieces, instructions, and a fitted foam case. Total shipping weight with eyepieces and case is 35 kg (77 lb).