Wider field of view for book scene.

rtiow/src/scenes/book.rs

@@ -28,7 +28,7 @@ pub fn new(opt: &Opt) -> Scene {
         lookfrom,
         lookat,
         Vec3::new(0., 1., 0.),
-        50.,
+        20.,
         opt.width as f32 / opt.height as f32,
         aperture,
         dist_to_focus,