If your main interest in astronomy is exploring fine detail on planets or showing structure in distant galaxies, "astronomy binoculars" are not for you - they just don't have enough magnification. However, if you thrive on large open star clusters and big, extended nebulae, a binocular can actually be more effective than a telescope. In fact, a binocular is one of the best "first telescopes" you can buy and even an experienced pro usually keeps one by the telescope.
What prism type is right for astronomy binoculars?
- Porro prisms, with their superior light transmission (no mirrored surfaces) and inherent image sharpness (no phase-shift) rule the roost here. There are a few 9x63 roof prisms floating around the market from time to time, but unless they are PC roof prisms, they will not be as sharp as the same size in a porro prism.
- Bak-4 glass is the preferred glass for a porro prism and will give brighter and sharper images than inexpensive BK7 prisms. All but the cheapest astronomy binoculars will have the superior Bak-4 glass.