Tip 9: Select Your Render Area
Setting up a 3D scene, adjusting the lighting, and tweaking the viewing angle can all take a while—but nothing takes as long as rendering your scene to see if it works. To cut down the waiting time, consider rendering just a portion of the scene rather than the whole thing.
Make a rectangular selection with the Marquee tool, and then use the Render command. Only the selected area will be rendered. This approach is much quicker than rendering the entire scene, and you can use the technique to focus on a small area of interest that you want to get right—the softness of a shadow, for instance.
If your object takes only a portion of the canvas, make a rectangular selection around it before rendering the whole thing (see Figure 9). Otherwise, Photoshop will render the entire canvas, and you'll waste time while the software attempts to work out what's going on in the blank areas.
Figure 9 When you just want to check your settings, rendering only a portion of the image saves time.