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If you'd to add motion blur to your renders when you are working with mental ray, you can find the controls for this in the Render Settings window. So, I am going to go to Window > Rendering Editors > Render Settings, and I am going to move to the Quality tab here, midway down, under the Shadows, you'll find the Motion Blur section. This is how you turn motion blur on when rendering with mental ray. You have a few choices here: Off of course is no Motion Blur. No deformation is for objects that are simply moving past the camera, like the sphere here or if the camera is moving past an object or both.
Enfold is for deformed objects, such as characters that are moving arms, character that has been rigged, joints or deformers, and now he's moving his arm or some part of body past the camera quickly. You want to use Full in that case, so that it calculates the Motion Blur correctly. Now I am going to set this to No deformation, so that is on now, and I am going to create a render using the default settings. And there you can see that it's been blurred, and the textures have been blurred, as well as reflections. You can also see there is just a slight blurring to the shadow, as well.
So, I am going to store this. I can increase the scale of the motion blur, the amount of motion blur by increasing the Motion Blur By setting. So, if I set this up to 3, I should see something a bit more dramatic. So, now we can see I have got a lot of blurring going on, but you also note that the blurring is fairly grainy. So, to improve the quality, to remove some of the graininess, I can actually change the Time Contrast, under Quality. Lower value improves the quality but increases render time.
So, if I set this down to something like .05, and I'm going to store this image and create another render, you will see that it does take longer, but the quality will look a lot better. So, I can compare this, store that image, and compare it. See, there is less grain there. With things like motion blur, you can get away with little bit of graininess. You should test short sequences of your animation and see how much you can get away with. By lowering the Time Contrast, I've increased the render time by five seconds on this machine.
So, it's fairly significant, and adds up in animating sequences. A couple other things you can do to optimize scenes with the motion blur is that if I select an object here, such as the sphere, and I go to the Attribute Editor on pSphereShape1 tab, the tab for the shape node, under Render Stats, there's a Motion Blur option. I can turn this on or off, so it will calculate motion blur on a per-object basis. So, if you have a scene with very slow moving objects mixed with fast-moving objects, you might want to turn this off for slow moving objects, or objects that don't move at all.
So I can select this and turn this off, and now it's not going to calculate Motion Blur. Since my camera is not moving and the plane is not moving, there is no reason to calculate motion blur for the plane, so I can turn it off. If you have, let's say you are renderings something like an asteroid field that has 476 slow-moving asteroids and one fast-moving asteroid, a quick way to turn off motion blur for the 476 asteroids is to go into the General Editor and go to the Attribute Spread Sheet, select the slow-moving objects in your scene, go to the Render tab here, and under Motion Blur, you can select this.
It will select all of the objects in the column, and then just set this to zero. So, that turns it off; setting this to 1 turns it on. This is a good way to deal with scenes where you have a lot of objects. A couple of other things I'd like to point out here in some of these settings. The Motion Steps feature, a good way to demonstrate how this works is I'll have an object in here, just select the object and do Shift+H to unhide it.
It's kind of like a helicopter blade. Let me minimize for the moment. If I play the animation, you can see it's just spinning around here. So, what I am going to do is pull up my render view, and I am going to create a quick test render. So, you can see how you have this straight edge right here on a spinning object. It was not terribly realistic, because the object is spinning, so you'd expect this to be more of an arc rather than just a straight edge. So, I am going to store this image, minimize it, go to my Render Settings and increase the Motion Steps. This is the number of times that the motion blur is calculated per frame.
So, if I set this to something like 6, and store this image and create render, now you can see we have a nice arc to the blur, which looks more realistic. So, if you doing like a helicopter blade, or something like that, or a propeller, you want to make sure that you increase Motion Steps so that it renders correctly with the blur. Last thing I'd like to point out is the Shutter Open and Close settings. When motion blur is calculated in the real world, imagine that you are taking a picture of a moving object, it takes time for the shutter on the camera to open. Then the shutter is open and exposes the image, and it takes time for the shutter to close again.
So, we have time at the beginning, in the middle, and at the end. These two settings determine how much time it takes for the shutter to open and the shutter to close. So, if I have Motion Blur set to 3 here, and I start to increase this, that if we look at zero at the beginning of the frames, say, frame 50, as I move this up, we are moving closer to the middle of that frame. So, I'll set this up to .5, and what you will see is - I am going to go to the render view window, I am just going to sample an image here, and render just that region.
What you can see, it's going to decrease the amount of blurring, but it's cutting off the beginning part of the blur. Same with if I a decrease Shutter Close, that's cutting off the end of the blur. Realistic Motion Blur, of course, there is blur ahead of the object and blur behind the object created by the mechanics of the camera opening, because the object is moving while the shutter is opening and closing. So, you get blur at the beginning and the end. But you control exactly by adjusting these two values.
If both of these values are set at the same exact value, in other words if I set this to 0.5 and 0.5 and do another render, you are going to get no motion blur, These are at exact same time. So, there is no time at all for the shutter to open, or no time for the shutter to close. It's just showing, exposing the negative, and that's basically what's happening. So, these are some of the settings that you can adjust to both increase the efficiency and the quality of your motion blur renders.
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