So far I've been using the following setup to render the pure object-shadow in a studio environment. Rendered with BlenderRender and than composed in Photoshop.
But since the fact BlenderRender will be removed in 2.8 I'm searching for the same result in Cycles. There is this new Shadow Catcher option but I'm missing settings for factor and distance. Rendering an AO Pass only gives me a gray object color with shadows.