Turning off the Lighting, scroll to V-Ray :: Global switches, as well as clearing the On check in the volume of V-Ray :: Indirect Illumination (GI) - the scene is not a single light source, not directly not secondary. That is why, the whole scene, with the exception of material VRayLightMtl, - is black.
Nothing to do not need to think out, simply follow the instructions above in the text 😉
Hello!The answer to this question is situational.If we talk about whether it is worthwhile to do such "clumsy" renderers, which then need bugs and "zapilivat" render-elements, then there is no answer. Precisely not worth it. In the "clumsy" renderers and render-elements "clumsy"😁 Pulu from himself you know what can not be molded.If we talk about a specific situation, for example, about the allocation of an object or the creation of post-processing depth of field, then without the Alpha and Z channels it is simply indispensable. And then the answer is yes, it's quite rational to use some rendering elements in postprocessing as auxiliary clipart files.In other words, ideally, you need to learn how to make renderers that do not require any post-processing in any form, while some visual effects are trivial to make fasting rather than bother with setting up the scene. For example, in addition to the above-described alpha and zeta, in the same Photoshop you can "spotlight" reflective materials using the Reflections element, using it to create a selection and then "highlighting" this selection with the same Curves. This approach is easier and faster than, say, "honestly draw" highlights in the 3d scene by placing dozens of reflectors or additional. Light sources behind the scenes for dozens, for example, 3d models of utensils of various shapes arranged in different places of the scene, so that only "glittering glasses" were on the render of the usual kitchen. That is, according to the situation.Rende-elements are not a standard mandatory for use, but only helpers in case "it is more convenient"😉