I am viewing a 3D scene using the viewport. This problem also appears when using the Render button. I am having black results for my Glass BSDF stones. When I zoom out, I get black results. On the contrary, when I zoom in, I get good results. How can I achieve good results in every case? Blender 2.77a
I include a short version error: https://dl.dropboxusercontent.com/u/3322974/BlackStones.blend
Hardware: Mac Pro 5,1; Memory 24gb; 2 processors 2,26 ghz; AMD Radeon HD 7950 3072 MB; OSX El Capitan 10.11.5; Rendering using CPU