EyeonTips:Manual/Tool Reference/Particles/pCustom

From VFXPedia

Particles just disappear when they intersect the clipping plane of the camera. This causes a visible pop in the image which can be distracting. This tip demonstrates how the pCustom tool can be used to create a soft clip region for the camera, by fading out the particles before they reach the clipping plane.

Particle ID

When emitting one particle per frame you can use the lifespan and age to calculate a unique ID for each particle:

(age*lifespan-time)*-1

To better visualize what the particle ID does, create a pEmitter with the emission rate set to 1 per frame. In a pCustom tool enter id/50 as red expression and if(id=4,0.3,0.1) as size expression. (source: this pigsfly post by Gringo)