Rendering group> Depth of Field

Trapcode Particular mimics the look of a real camera by adding a Depth of Field (DOF) simulation.

How does Depth of Field work? A real camera cannot maintain focus in all depths of an image. DOF mimics the way that a real camera cannot maintain its sharp focus at all depths. DOF is useful for increasing the realism of a scene. It is also useful for matching your Particular effect to footage shot with a real camera where Depth of Field is apparent.

By default, DOF is turned on with the Camera Settings option. Choose the Off option to turn off DOF. Let's look at how to use it!

Version 1.5 Note: DOF was previously turned off by default, and turned on with two Render Mode settings. New to version 2.0, the DOF render is now automatic. You will notice Depth of Field referred to in some Particle Type options with a 'DOF' indicator.

Tutorial: Simulating Depth of Field
Make a new comp (Ctrl/Cmd-N). Make it NTSC D1 Square pixel at 30 fps. and 5 seconds long. Create a comp-sized Solid (Ctrl/Cmd-Y), choose Make Comp Size, and click OK. Apply Effect> Trapcode> Particular to the Solid.
Make sure your Time Marker is at Time 00;00 (Frame 1) of the comp. From the Particular preset popup, choose the preset 'Grid Across'. Now create a camera (Layer>New>Camera) and use the 28mm preset. Go to Time 04:00 (4 seconds into the comp) so you can see some particles.
Let's make the particles shoot even closer to the camera. Choose the Particular layer and go to the Effects palette. Change Emitter>Y Rotation to 44 degrees (it was 55 in the preset). You should see this:

Depth of Field is turned on by default in Trapcode Particular. That is the function of Depth of Field> Camera Settings, which is active by default. There is a Depth of Field Type control below it. When using a simple Particle Type like Sphere as we are doing here, it does not matter if Square or Smooth DOF mode is used. That's why this control is grayed out for the Sphere particle.
Now we need to enable DOF on the AE camera. Select the Camera layer in the Timeline and twirl down its Options.

Set Depth of Field to On. Set Focus Distance to 150 pixels. Set Aperture to 100 pixels. This setting is unrealistically high, but useful for quickly understanding how DOF works.
Now you should see the partially blurred image below. Drag around the Focus Distance slider a bit and see how the focus plane moves in and out if the image.