Imagine this scenario; you're working with a client who wants you to turnaround a finalized render in a few days. You spend the entire week dialing in all of the details, creating intricate lighting, realistic materials, and high poly models. You finish your scene a couple of days before the deadline, so decide to run the renders at the highest settings possible at the highest, most feasible resolution, just to treat your client to the perfect rendering that you're passionate about. 'There's no way this single render will take two whole days,' you think to yourself. A couple of days pass - the deadline is approaching - you check the progress on your render only to find that it's only halfway done, with the estimated remaining time to run well past the deadline. What went wrong?

If you're an experienced 3D artist, it may come as no surprise that sometimes, exceedingly long render times may lead to you cutting it close with your established deadlines, leaving no room for corrections should you need to make any. In many cases, this might be due to your render settings being exceedingly high along with your render resolution. The obvious solution to cutting down on these render times is to decrease your render settings to something feasible - experiment with your settings to find the right balance between preserving visual details and cutting render times short. However, there are many not-so-obvious tricks you can make to further decrease your render times outside of just lowering your settings.

1. Skip using Ambient Occlusion

Ambient occlusion is a computation performed to calculate how exposed each point in a scene is to ambient lighting. When two points of contact are close together, those points will be rendered darker than if they were completely separated. In the world of 3D, this technique is used to add contrast into the scene, and is most commonly associated with the visual fidelity of most modern video games. Ambient occlusion is also heavily utilized in the world of CGI and architectural visualization.

Ambient occlusion is extremely useful in adding contrast to your scene and making a render's shadows "pop out" more to the viewer, but using ambient occlusion does come with the unfortunate side effect of increasing your render times. In V-Ray for 3ds Max, ambient occlusion is commonly rendered as a separate render element using the V-RayExtraTex (V-RayDirt) node.

As an experiment, I rendered a small scene with the V-RayExtraTex render element turned on, and then with it turned off. I noticed that with the V-RayExtraTex render element turned on, the render took two hours and fourty seven minutes to finish, but with it turned off, the render finished in an hour and twelve minutes. I ran this experiment with a couple of bigger projects, and noticed a significant decrease with ambient occlusion turned off as opposed to it being turned on.

If a deadline is rapidly approaching, and you need to run your renders much faster, I highly suggest temporarily not using ambient occlusion, or if given the option, rendering it separately from your base RGB/Beauty passes.

2. Check your displacement settings

Many renderers and modeling software may offer several options on how artists can tackle the usage of displacement. With 3ds Max and most of its compatible renderers, there are modifiers and material nodes that artists can use to simulate displacement. Since we're on the topic of V-Ray, let's talk about using displacement in V-Ray.

As stated before, 3ds Max allows users to simulate displacement through its material nodes and with modifiers, and V-Ray follows these standards closely by having its own modifier and material displacement node. V-Ray's material displacement node is self-explanatory; you plug in a displacement map into the node and decrease the value next to it to something feasible like 0.25 or 0.5. On a three dimensional object, you may need to chamfer your edges to ensure that the object properly displaces around the corners. In most cases, this should be enough to simulate the displacement that you're looking for in a scene, but there's another option you can take to simulate displacement in your V-Ray scene.

The VRayDisplacementModifier is a modifier that V-Ray offers artists that gives them more control over the quality, size, and even the method used for your displacement. Typically, this modifier improves the quality of an object's displacement, but an unfortunately consequence to this is that it increases your render times. According to the documentation, the VRayDisplacementModifier is capable of three different types of displacement - two of which precomputes and subdivides the mesh and applies a displacement map to it, while the last one - mostly used in landscapes and flat surfaces - "renders the mesh as a warped height-field based on that texture map."

With the subdivision and 3D mapping methods used, the difference in render times is not significant, as the mesh is computed and subdivided at runtime. Typically, the most significant effect that you'll see is a longer time "compiling" meshes while your scene is starting to render. The 2D mapping method makes a significant difference in your render times, however, due to how the displacement is computed using that method.