Bright optics

Since the invention of the telescope, the cry of astronomers has been, “More light!” – you want as much as possible of the light gathered by the objective lenses to be transmitted to your eyes. The Spezial Astro SF 15x70s meet this requirement: there is none of the stopping down of the light cone that some binoculars use to reduce aberrations and sharpen the image, although there was a minuscule obstruction from a component in the prism cages. This in turn requires that optical aberrations are well controlled. Except at the very edge, you will experience a flat field of view, with sharply focused stars and very little false colour. Finally, where the light meets a glass surface, reflection must be minimised, something achieved with anti-reflective coatings. Shining a torch into the lenses suggests that their glass-air surfaces all meet the “fully multi-coated” specification. This is a reassuringly bright pair of binoculars.