National geographic porro prism zoom binoculars 50mm national geographic 9064000 these 8x 24 x 50mm porro prism zoom binoculars from national geographic offer an attractive zoom function and variable magnification the fully coated optics guarantee a decisively higher light transmission through the glass increasing colour fidelity and contrast diopter compensation is standard while the package also includes a carrying pouch and neck strap for longer observations a tripod adaptor thread i