Designed for medium to long range terrestrial and astronomical observations the helios apollo 15x70 ms observation binoculars are waterproof nitrogen filled and shockproof due to the all metal body construction featuring bak 4 prisms the binoculars have a multi coated optical system that allows for 92 light transmission and distortion free images the long eye relief and fold down rubber eyecups make these binoculars suitable for spectacle wearers and the tripod mounting bush and threaded