This post is about creating motion blur and depth of field using Vray for Cinema 4D. While there are already a couple tutorials out there they all leave out one important detail. Following the instructions it's relatively easy to figure out how to turn these features on, but you also have to know that the Vray physical camera behaves exactly like a real camera and needs to be adjusted accordingly. So let's start off with motion blur since that's a little easier.
Here's the basic scene we'll be dealing with. It has a physical camera, a light with physical sky and sun enabled and some quick global illumination, because that's the whole point of Vray, right?
Next I add the VrayMotionBlur tag by right clicking on the object and going through the menu. The other step that is required is to go to the sampling tab of the camera parameters and turn on MBlur.
Now if we render we see that there is a little bit of motion blur. So we're already off to a good start but I want something a little more dramatic. So the secret to increasing the amount of blur is to adjust the shutter speed of the camera. I like to have the "Fixed exposure increments" turned on so that I can adjust in the same increments you'd get when working with a real camera.
I won't go into too much detail about how a camera works, there are innumerable resources already for that, but here are some basics. The shutter speed determines how quickly the shutter in the camera opens and the closes again. The faster the shutter the less time there is for the film/image sensor to absorb the light and capture the image, but this also means less time for the object to move. This can result in even fast moving objects being frozen in time and look like they're standing still. But what we want is a longer exposure giving the film time to "see" the object in motion which result in the blur when want. So decrease the shutter speed by several stops. Since we have decreased the shutter speed a lot more light is going to be entering the camera (because it has a longer period of time to do so) so that is going to increase the exposure of the image. To maintain the exposure we had we could either increase the film ISO or increase the F-Stop. I'm choosing to increase the f-stop, and because I have "fixed exposure increments" active its really easy. If I decrease the shutter speed by 3 1/3 stop increments (or 1 stop) then I just have to increase the F-Stop by the same amount.
This is the result of a shutter speed of 30 and a F-Stop of 20
One last comment about motion blur. If you want to create motion blur caused by movement of the camera keep in mind that Vray seems to ignore expressions when determining if the camera is in motion, so if you have your camera following a path for example it won't work. You have to bake the expression to keyframes.
So now that we've got control over motion blur lets work on a scene with some depth of field. I've found this one to be much trickier because even when you have all the settings activated it still won't be visible, again this is because of camera physics.
To turn on Depth of Field (DOF) go to the Sampling tab of the camera and check the "DOF on" check box.
The next step is to tell the camera what to focus on. To do this you can manually enter the "Target Distance" in the parameter under the "Depth" tab in the camera attributes or you can drag the center orange dot widget on the camera object itself. Or if you're using a target camera it will automatically focus on the target. When you hit render it will probably look exactly the same. Now it's time to play with the physical camera tag.
The trick to depth of field is having a wide open aperture(Vray simply calls this F-Stop), but as you recall from the motion blur example adjusting one camera property has effects on the others. For this example I've lowered the F-stop by 16 1/3 stops and increased the shutter speed by the same amount.
Composition is just as important as camera settings are to achieving beautiful depth of field. The greater the physical distance between the background and foreground elements the better. If you want the background to appear very blurred but also want it to appear close try moving them apart and then moving the camera backward and zooming in, this will compress the distance and make everything seem closer together.
Keep in mind that there are limits to what this physically based depth of field can do. I had hoped to demonstrate depth of field with something like a piano keyboard but even with the most extreme settings I was not able to get the depth of field narrow enough for my liking.