It is always a good idea to do effects such as Motion Blur or Depth of Field in post, and not in the native raytracing render engine. As otherwise, this will massively increase render times. The next tip is based around this workflow for creating correctly using a Z depth in 3ds Max Composite to create a depth of field effect.
This next tip is something I was guilty of getting wrong for many months. In short, make sure you invert the Z depth element when using Composite with 3ds Max renders. When rendering Z depth from 3ds Max Composite ensure you add an Invert node to the element for it work accurately in post.
In this tip I am assuming you have some knowledge of importing and working with rendered frames. If you have never used 3ds Max Composite before I recommend, you work your way through the ‘Essential Skills Movies’ (tutorials) that you should be confronted with the first time you open Composite. Seen below.
Now lets look at the steps needed for a ‘correct’ Z depth.
1. Render a Z depth separate element, ensuring the min/max settings, found in the element parameter options, are correct for your scene. These settings will change on a scene by scene basis. (This has been discussed in previous posts, so I wont be discussing this part.)
2. Open your 3ds Max Composite Node flow. For the purpose of this tip I have kept it to a very simplified flow.
3. Import your Z depth render. (or duplicate the OpenEXR file, and enable the Z depth Channel View)
4. Add an ‘Invert’ node from the gateway user interface>tools. (middle mousse button), and scroll to the ‘Color Correction’ Category. From here the Invert tool is listed.
5. Now connect the two nodes together, similar to the below flow. After they have been connected add a blur node. (follow above procedure, but looking in the ‘Filtering’ category.) You can choose ‘blur’ or ‘lense blur’.
6. Now you have a ‘correct’ z depth pass for use with Composites toolsets. When applying post effects, composite will recognise the correct values. Rather than the previous inversion you may have experienced.