* Astronomy

Revelation 15x70 Binoculars are larger aperture binoculars ideal for astronomy including deep sky work and lunar observation. This model also allows for higher power daytime use at 15x yet are still light enough to carry around. Superb for long distance observation of wildlife, shipping and sports where maximum handheld power and light grasp are required.
Very well suited to high power low light terrestrial work where the large 70mm lenses will gather over 50% more light than 50mm models meaning these are especially useful at dawn and dusk. Being light and well balanced they are suitable for handheld or tripod use. These superb binoculars incorporating BAK4 prisms with fully multicoated optics are perfect for all applications with their larger lenses and higher magnification.
The model also includes interpupilery and diopter adjustment with long eye relief. Includes tripod adaptor bush and soft case and neck strap. The long eye relief eyepieces are suitable for spectacle wearers and have comfortable fold down rubber eyecups.

Telescope House are selling the outstanding Revelation 15x70 Binocular for £49.00

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Leica
This year, the Ultravid spawned the even brighter, sharper Ultravid HDs, with fluorite glass in every lens. Exposed surfaces wear proprietary AquaDura lens coating, a hydrophobic compound that beads water and aids cleaning. Ultravid HDs come in 8x32 and 10x32; 7x42, 8x42 and 10x42; and 8x50, 10x50 and 12x50. The latest Geovid laser-ranging binoculars are available in 8x42, 10x42, 8x56 and 15x56. Weights range from 33 to 39 ounces. Other recent developments at Leica: Duovid 8+12x42 and 10+ 15x50 binoculars that afford you a choice of power with the turn of a dial.

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For the most part, when people think about astronomy they picture hobbyists with huge, mounted telescopes that have high zoom ratios, are quite expensive, and difficult to use. What most people don't realize is that a good pair of binoculars is actually the viewing tool of choice for most amateur astronomers.
While both actually have their strong and weak points, knowing the differences between the two can help you decide which viewing tool you'll wind up needing for yourself.

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BaK4 and BaK7 Glass are the two types of glass most commonly used in binoculars.
Generally with low power binoculars BaK4 (Barium Crown) is preferred over BaK7 (Borosilicate) because of the increased light transmission resulting in higher edge sharpness and greater brightness.
However BaK4 may introduce chromatic and spherical aberration.
BaK7 prisms are best used in high powered binoculars because of the defect-free optical properties of the glass.
To check if binoculars have BAK-4 prisms, hold the binoculars up to the sky at arm distance and look into the eyepiece; You should see a clean circular image. BK-7 prisms will show a squared-off, non-circular image.