I'm creating an underwater shot sequence, and I have a submarine w/ particle emitters attached to each propeller, so that it leaves a small, "corkscrewing" trail of bubbles in the prop wash. I thought it might be better to create geometry for the bubbles and instance them to the particles (so I can render the scene in one pass), rather than using the particle/spheres themselves (w/ a hardware render) and compositing them afterwards (the rest of the scene looks so much better with a software render). My problem is I don't know how to get these "instanced" bubbles to vary in size (which was easy to do when they were particles).
Any suggestions on how I might achieve this would be greatly appreciated.