CALayer *capa = [self.navigationController navigationBar].layer;
    [capa setShadowColor: [[UIColor blackColor] CGColor]];
    [capa setShadowOpacity:0.85f];
    [capa setShadowOffset: CGSizeMake(0.0f, 0.5f)];
    [capa setShadowRadius:5.0f];
    [capa setShouldRasterize:YES];